Alert!
This lesson's lab experiment uses dangerous voltages, and currents. If performed incorrectly your likely hood of survival is rather low. Performed correctly, using the precautions I describe here in, raises your likelihood of survival to a level comparable with walking across the street, on a green walk light, or driving down the freeway at a safe and prudent speed. People still get squashed by a bus walking across the street, while doing everything in their power to observe well known safety rules, and while employing common sense. Safety rules do not guarantee survival, but they help tremendously. Furthermore upon hearing of news that someone was squashed by a bus while walking across the street, seldom deters onlookers from walking across the street an hour later, they simply look death straight in the eye, and stare him down, resolving to do everything in their power to avoid getting squashed, but not to the exclusion of walking across the street, they merely do so carefully. The danger this experiment exposes people who carry it out to, will probably kill one person in 10 billion, even though they meticulously follow my instructions. If these odds are too great for you, my advice is to become a shutin, never venturing out into the dangerous world around you, and stop taking this course. Life is a "Calculated Risk" there are no guarantees, not even that you will survive. I offer no guarantees that my experiments are safe, indeed, I am telling you that they are not safe. That said I do my best to outline reasonable precautions that will greatly increase safety, but the risk is yours, I cannot be responsible for the myriad of mistakes people will make. If I tried to plan for every conceivable eventuality, one, this web site would never be completed, and two, every contingency planned for, potentially introduces even more risk so such planning is doomed to failure anyway. This experiment, as do all of my experiments, teaches something important, this one demonstrates in a very enlightening, and hands on way, the difference between reactance, and resistance. It leaves a lasting impression of just how different they really are, but to do this requires several watts of electrical power, at voltages, that are high enough to be dangerous. Using lower voltages would make the experiment unreliable as obtaining the specialized components could not be relied upon in the kind of setting this Web based course is designed to be used in, where you the student are required to locate all of your own components. And let's not forget, someday sooner or later, you will have to work with dangerous voltages, better you become familiar with techniques that can offer a reasonable margin of safety now, in a somewhat controlled setting, than later in a setting where a snap decision proves fatal.

If you feel uncertain about any of the safety information I provide, talk to someone who is experienced in working with electricity to get clarification on the points you are fuzzy on. Make sure you understand the "whys" of the dos, and don'ts before you attempt the experiment.

Under no circumstances perform this experiment without listening to all the audio, critical safety information is contained in the MP3 audio that is part of this page, among other things I discuss the three levels of separation, some people call "Fail Safe" that must be observed at all times when working with dangerous voltages. To be electrocuted all three have to breakdown, this is what gives you relative safety. I go way overboard on this but I assume you are a novice, and as such, since I cannot be there to watch you, the best I can offer are a set of rules, silly as they may seem, they are not silly if they save your life. Sooner or later you will have an incident when one of them break down, the other two, because they were in place, are what is saving your life, later when you have time to reflect you will understand why they are not so silly after all.

In the audio I discuss having a onlooker in the room to break the circuit, and render assistance should the need arise. Make sure that this person knows that they are to pull the plug of the extension cord from the wall socket, not the table leg end, in the event of a mishap, and that they are not to touch you, until the flow of current has in this prescribed way been stopped! If they were to touch you... and this is what an untrained person is likely to do, because they instinctively will attempt to pull the victim away from the live wire. Doing this will likely get them electrocuted as well! Make sure they know how to contact emergency medical assistance by phone, and if they are trained in CPR, Cardio Pulmonary Recessitation, so much the better, but call before attempting recessitation, and when they place you on hold, turn on the speaker phone, and attend to the job of recessitation.

Click the "Audio discussion" link now, then
read on while it's downloading. When it    
arrives, come back here, to start, and as I
progress through the audio discussion, I'll
instruct you to proceed from one pictorial 
to the next, like a slide presentation
  • 014_Setting_up.mp3 Audio lecture on setting up a high voltage work area 8.79 meg

    • Experiments using real electricity

    Your Notes:

    This lesson segment is nearly all lab, and when you complete this lab you will have some additional useful test equipment. The first item, the Home Brew Isolation Transformer, is to be built only if you have on hand, two large, eg. in the range of 300 VA, eg. 300 watt, or above nearly identical 120 volt primary to some other voltage secondary transformers. If you don't already have a couple of these sitting around unless you happen onto a couple of them, real real cheap, you are probably better off buying an isolation transformer. Mouser has one for $62.16 that delivers 2.1 amperes, and considering the effort you'll put into building one, you better not have paid very much for the two transformers that makeup this project. What is meant here by nearly identical, is one, the VA ratings are within a two to one ratio, one to one is ofcourse best; and two the secondary voltages of these transformers is within a ratio of 1.0:1.1 that means as an example, that if one of the transformers secondaries was 24 volts at 15 amps, and the other transformer was 28 volts at 25 amps the pair would not be suitable for this use, because 28 divided by 24 is 1.1667 and that is just too high, even though the power levels are fine. 24 times 15 is 360 watts which is plenty of power to build a 200 watt Isolation Transformer.

    However upon looking at the primaries of the larger one, you happen to notice that it's primary has an extra set of terminals for a tapped primary input voltage that will allow an input of 130 volts. See the second picture in this page, titled "Multi-tap Primary Transformer" Upon running the ratio numbers you would discover that deliberately setting the wrong tap, making the transformer a 130 volt primary, and then running it on 120 volts, a lower voltage than it was designed for won't hurt anything, and it changes it's output voltage from 28 volts to 25.846 volts. Now the voltage ratio of the two transformers is 25.846 divided by the other transformer's secondary of 24 volts gives a ratio of 1.077 to 1 which makes it a perfect choice. It will run the small transformer a little bit hard, but losses in the total system will be somewhat canceled, by the fact that you are driving it a little harder than the absolutely correct voltage.

    A safety issue here to consider is that if the secondaries are a high voltage, like say 700 volts, you probably shouldn't use these transformers as a Home Brew Isolation Transformer because if the insulation should break down, or moisture were to condense in just the right places the isolated secondary could be giving off a very high voltage with respect to earth ground. I mention this here, primarily because one might be tempted to use a pair of transformers culled from two old worn out Microwave Ovens. This is tempting because they handle about a thousand watts, and you could easily build a five hundred watt isolation transformer from two such transformers. My feeling is that it isn't worth the risk, I wouldn't use a transformer for the purpose of building a Home Brew Isolation Transformer that stepped up more than double the line voltage as a rule of thumb. Using step down transformers for this purpose is always safer.

    I have found sources some of the parts for this and other experiments. I am not necessarily recommending them, just mentioning them as a possibility, you should scout out your own home stomping ground for sources of these materials and don't overlook Flea Markets, Ham Fests, and Army Surplus stores. 

    Switches suitable for the Dead Man switch
-------------------------------------------
Vendor      stock nbr   rating        price
Radio Shack 900-8572   6 amp/250 volt  3.69
Mouser      103-4025   6 amp/125 volt  3.18

Thermal fuse suitable for Isolation Xfmr
-------------------------------------------
Vendor      stock nbr   rating        price
Radio Shack RSU 11308467   189 deg F   1.29
MPJA        5357-TF        91 deg C    1.00

Neon indictor lamp assy
-------------------------------------------
Vendor      stock nbr   rating        price
Mouser      36HN010   110 volt         1.82
    About the Mouser 103-4025 switch, neither the Mouser, nor the Radio Shack version, is a true push button, rather both of these are "Momentary Toggle" switches, that is they have a spring action that upon release return them to the previous position, the Mouser version offers a small safety feature in that it's lever is made of insulated plastic.

    As an alternative you could mount two SPST Pushbutton switches, one on each side of the box, arranged so that your thumb and forefinger can press both buttons simultaneously, in a squeezing motion.

    Oops I just threw in a another term you might not be familiar with, what is SPST, it stands for Single Pole Single Throw. Ya' fine you say now that does that mean, Ok Ok I'll get there. You will see switches designated by acronyms like SPST, where sometimes the "S" is replaced with "D" meaning Double. Think back to the days of early electrical experimenters, most famous among them being Doctor Frankenstein, or maybe Dr. Tesla comes to mind, not that he was ever on a par with the other :-) In their labs when Hollywood needed to Juice things up there was the closure of this really nasty, menacing looking Knife Switch, that always went sparky sparky when it was operated. It is that Knife Switch that will serve as a good memory gimmick to help you keep straight what things like SPST means. The Poles, are the Knife blades, that swing from one throw to the other, in a real Knife Switch, the kind Hollywood uses for effect they look like Poles pivoting on the center contact. The action of Throwing the Switch, is that of moving the Pole to a different Throw. Therefore a Double Pole switch is one that has an insulator bar with handle, that links both poles together so that the hand that throws the switch causes two circuits to change simultaneously. A Double Throw switch is one which has contacts on both of the positions that the switch can be toggled to. As an example the four wire pushbutton switch I show as the Deadman Switch is a DPST switch, as an exercise to insure you really grok this stuff, a DPDT has six wires, a SPST is a two wire device, a the SPDT is a three wire switch, a SP6T is probably a rotary switch, the kind with a knob, and six positions, and it has seven wires. Similarly a 4P12T switch has 12 positions and 52 terminals for wires, think old fashioned mechanical TV Tuner, my were those things complicated!

    The MPJA (Marlin P Jones and Associates) 5357-TF thermal fuse has a screw mounting ear to fasten it down the thing, in this case the transformer, that is to be protected from overheating. The radio shack thermal fuse poses an interesting problem, to pick up temperature it must be provided with a thermal connection to the thing that is to be protected, on the other hand it's body is electrically connected to the AC power line! So you need a very special electrical insulator. While it must be conductive of heat, it must not ever become conductive of electricity, this is especially vexing because many such thermally conductive, electrically insulative materials, melt at high temperatures. Melting would allow the body of the thermal fuse to make contact with the body of the transformer, causing it to carry the dangerous AC line voltage. There are special heat conductive Epoxy compounds designed to address this need, and there is a product called Silpad which is an adhesive backed sheet material, looks rather like adhesive tape, that is impregnated with thermal conductive Silicon. The Silpad samples I have seen are about as thick as Duct Tape, and are pre cut into various shapes, placed onto Release Paper, like Postal Stamps. If you were to cut a strip out of a coffee can a half inch wide, and 1.5 inches long, you could drill 3/16" holes in the ends, and bend it into a "P" shape clamp around the electrically hot thermal fuse, that has been prewrapped with Silpad, and the wire ends should be covered with shrink tubing after soldering insulated wires to the ends of the thermal fuse.
    Assembly of Isolation transformer
    The material you would choose for an enclosure for your homebrew isolation transformer should be plywood, Masonite, or plastic. Do not use metal, the whole reason for building an isolation transformer is to block a direct path of current from the powerline to you. Each of the two transformers are capable of providing a level of isolation, unless... If you mount them in a metal enclosure, the enclosure itself can provide an unfortuitous path bypassing part, or all of the isolation. On the other hand, wood is a fire hazard, it's a little like having to choose between the lesser of two evils. That's why I spend so much time on thermal fusing the power input transformer. Transformers are particularly problematic from the standpoint of fire safety. If a short circuit between any two adjacent windings inside the transformer's coil occurs, what you have is the mighty output of the entire transformer, its combined turns ratio, of its primary winding stacked against that single shorted turn. The shorted turn can be anywhere in the transformer, primary or secondary, the end result is the same. The entire output is diverted into this lone shorted turn. Such a single turn produces a very low voltage, usually a small fraction of a volt, at hundreds of amperes. The result is that it gets incredibly hot, and melts away all its insulation, and the insulation of nearby as yet undamaged windings. They too ultimately short, and now contribute to further destruction of even more nearby windings. This shorting of adjacent windings is not unlike a cancer of the transformer, and it spreads until the primary draws so much current that a wire burns open, or a fuse, or, circuit breaker blows. What you may not understand is that a transformer fused with a current limiting fuse, can because of this process, long before the current limit of the fuse is reached, create so much heat that the transformer will glow yellow hot! Such a transformer mounted to wood, can start a fire. That is why I spend so much time giving information of proper thermal fusing, a thermal fuse doesn't blow because the current has been exceeded, it blows, or opens because its rated temperature has been exceeded, which is precisely the proper way to fuse a transformer, then if you want to put in additional fusing, in series with the thermal fuse that is up to you, but the thermal fuse is critical.

    The base of the Isolation transformer wooden enclosure should be made of a thick plywood baseplate, say one inch thick. The sides, front, and rear, can be thin quarter inch plywood, or eighth inch Tempered Masonite, and Masonite is easy to work with, and looks good unpainted, however the top should be made of five eighth's inch plywood because this allows you a solid cross sectional area to sink your wood screws into for fastening the sides, front, and rear, panels. Finally place corner molding pieces in all four corners to provide solid pine to allow something for wood screws to sink their teeth into for fastening of the sides to each other. The base of the enclosure is ofcourse the surface that you mount down all of the heavy components to, such as, and especially the transformers. None of the screws should be long enough to protrude through the bottom of the cabinet, not only is this a potential electrical safety issue, but wood screws have sharp points, and sliding a heavy wooden cabinet with a sharp screw point sticking out of the bottom, will marr the surface of your nice Formica top, in a way that finished plywood by itself will not. The outlet receptacle should be mounted to one of the sides, being they are smallest Masonite plates, and the plate that holds the electrical outlet should have enough screws to hold it securely while things are plugged into, and unplugged from the electrical outlet that it is supporting. For screws consider using hardened steel drywall screws, these have a very aggressive thread pitch, and are kind to wood, in that they seldom cause it to split. If you are of a mind to use glue, I recommend building this cabinet in two pieces that fit together, one piece has the bottom, and the end with the outlet mounted to it, and the other is the the top, and the other walls, should repair ever be necessary, you'll be glad you made it that way. As for the wire that connects the two low voltage windings to each other, this needs to be very heavy wire, the lower the voltage they are, generally speaking the heavier the wire, a good rule of thumb is use wire that is atleast three gauge sizes lower, than the wire exiting the transformer. Note the lower the gauge size the larger the wire. By using wire three gauge sizes lower, you nearly double the cross sectional area of the current carrying copper wire.

    Construction Notes:
    Many of the construction techniques I show here are useful everywhere electronics projects are built by hand, therefore you should create a separate file in your "Electronic Notes" directory specifically for construction techniques, keep in mind my warning about avoiding Proprietary Formats from the end of lesson 010. It may sound a bit preachy, but the advice is essential to any creative endeavor, and this course teaches creativity, disguised as electronics. Maybe that is too strongly worded, you may have heard that creativity cannot be taught. I for one believe this to be true, but I also believe that genuinely creative people are easily duped into pursuing a life in which, their creative potential is never realized. Oh and by the way if you haven't already done so take a gander at my tool abuse page it shows how to think like a tool maker, as opposed to a tool user. For those of you running some variant of Unix, in the "X" window system, it can be handy to open multiple "Desktops" simultaneously, one catering to applications and files dealing with hardware notes, purchasing of, or acquiring free samples of parts, a drawing package for maps, and other doodles, and so forth, and another desktop for the study of electronics itself, and yet another for the browser, and its ancillary windows, this gives a nice uncluttered appearance, and beneath all of this are a dozen or so virtual terminals for those nice crisp Emacs screens that GUIs will never touch, oops way off the track, back to the project

    Assembly of Suicide Cord
    After building the Suicide Cord, you need to test it to be sure it is reliably safe to use. First a visual inspection before the box is closed up. You are looking for anything that could create an unplanned path of current. Multistrand wire poses a danger if a stray thin strand of wire accidentally makes contact with something that could carry current to you. Even if not actually touching something now, after the box is closed the wires may move, and if it were to make contact with something made of metal, such as the body of the switch you could get a shock from the push button itself. Use wire cutters to snip off any such stragglers, and use this technique to make a good solder connection in tight places. Make sure that all cords entering the box have some kind of strain relief. I will explain... The term Strain Relief is, in this sense taken to mean, the point where the wire makes entry to the box, the wire is securely fastened to the box such that a good hard yank on the cord cannot disturb the wiring inside. One way to accomplish this is to, prior to wiring the box up, drill a hole through the box, where you want the cable to enter the box, the hole should be no bigger than necessary to accommodate the wire with heated shrink tubing covering it. Next slide the wire into the hole, and from the inside of the box grab hold of the wire, and pull several feet of it through the hole. Now select a piece of shrink tubing that is about 4 inches long, and no larger than needed to fit around the cord. Slide it back about nine inches from the bare end of the cord. Now tie a knot in the cord, shrink tubing, combination such that the knot is centered so that there is a half inch of tubing extending from the knot toward the bare end of the cord, and the remainder of the tubing, probably two inches or so is extending toward the box, and plug end. Tighten the knot. Now heat the tubing with a butane lighter, with a smooth waving motion as you rotate the cord back and forth to distribute the heat of the flame evenly, so as not to scorch the shrink tubing, or the electrical cord. This will shrink the tubing down around the knot, and the cable, and when it cools it will be somewhat stiffer. Next pull the cable back into the box so that the knot rests against the inside wall of the plastic project box. Now use a Hot Glue Gun to anchor the knot securely to the plastic project box inside wall. Note: Rubber cement will work also but I caution you not to use Silicon Rubber glue, because it gives off Ascetic Acid vapors, long after the project is completed. These vapors over time will penetrate the enclosure of the switch and corrode the electrical contacts inside, rendering the switch useless, and perhaps dangerous.

    After the glue sets up, on the knots of both cables, and the box is wired and inspected, place the lid on the box, and screw in the corner screws. Now you are ready to perform a continuity test. Connect both clipleads together, and and clip them to one of the prongs of the plug, and use a separate clip lead to clip both ends of the plug prongs together, and clip the common wire of your Multimeter to the same mass of interconnected plug prongs, and clip leads. Set the meter to the highest Ohm scale possible, probably Rx10000, and momentarily test the meter by touching the other meter probe to a different point on mass of interconnected plug prongs, and clip leads, just to see that the setup is working. Now touch that meter probe to every metal object on the box, one object at a time, watching the meter, for any sign of conductivity. Do this once with the button released, and once with it held down. You are testing for any unforeseen electrical path to the surface of the box.

    Next unhook every thing, now connect one clip lead across the two prongs of the plug, and both clips exiting the Suicide Cord to each other, place one meter lead on the Suicide Cord's plug end, and one on the joined clips. This should show an open circuit while the pushbutton is released, and a closed circuit when it is pressed.

    Next disconnect the meter leads from the Suicide Cord, now separate the clip leads exiting the Suicide Cord from each other, and connect one each to the two meter leads, leaving the lone clip lead that is joining the prongs of the plug together, connected. Once again the meter should see an open circuit when the button is released, and closure when it is pressed. If these checks are good, as a last test set the Multimeter to the lowest resistance range probably Rx1, touch the probes together, to allow you to zero the meter, and then open them. Now pressing the button should read no more than a tiny fraction of an Ohm. If all these tests pass your box is ready for the final live test.

    Live Test:
    Get a working table lamp, plug it in, switch it on to insure it lights. Unplug it while it is working, and clip the two clip leads of the Suicide Cord to the prongs of the lamp's plug. Now observing all of the safety rules, and with an informed onlooker present, plug the Suicide Cord into the extension cord hanging from the table leg, nothing should happen, if anything happens pull the Suicide Cord's plug out immediately.

    Let me elaborate:
    As you plug it in be anticipating nothing, psych yourself to reflexively pull the plug out, as an automatic response to any kind of reaction, if the toilet flushes in the next room, just as you plug it in, and you reflexively yanked the plug out, because you heard something, after you calm down, you can always do the experiment again, once you've determined that the toilet had nothing to do with your experiment.

    If this phase of the test went Ok, press the push button, both the lamp, and the Neon warning lamp in the Suicide Cord's control box should light when you do this. Release the push button, and reach up and turn off the switch on the lamp, the Neon warning lamp should remain out, and it, and only it, should light when you press the button this time. Now for the final test press the button to insure that only the Neon warning lamp, lights as you push the button, and extinguishes when you release it, the table lamp should ofcourse remain out during this phase of the test. Now pull the plug of the Suicide Cord out of the extension cord's receptacle. If this phase of the test went Ok you now have a tested Suicide Cord, use it with care.

    What the final phase of the test is doing, deserves some explanation. Earlier tests determined that the push button switch when closed, could indeed deliver enough current to the clip leads to operate a substantial load, in this case the table lamp. The final phase of the test insures that with no load applied the Neon stays out, the reason for pressing the button, is to insure that the table lamp is indeed switched off, some table lamp switches, are designed for three way bulbs, and if you had one of these, and someone unbeknown to you, had inserted a regular light bulb, you may think you turned it off, without actually doing so. Pressing the button, the last time, expecting only the Neon to light, will alert you to this, allowing you to get this final phase of the test right. The purpose of this final phase, is to test your control box, especially the switch, for leakage current. If leakage current is low enough to prevent a Neon Glow Tube from lighting, it is below the level that is dangerous to people.

    Now you are ready to setup your breadboard. I will assume you have read through this entire page, and acquired the necessary components to build it. I show below a breadboard partially wired up for the first phase of the experiment. This is not intended to show you how to wire it up, that's what the diagram is for, rather this is to show in a general way how to make connections to nail heads, and device terminals, and the like. Start the download of the audio discussion, now while looking this experiment over, and when it starts playing place the drawing for the "Breadboard experiment" in the center of your browser's screen.
  • 014_HV_bred_bord.mp3 Audio discussion of high voltage breadboarding 8.41 meg

    • http://www.leviton.com/sections/prodinfo/lamphold/laframe2.htm#cats 
    Porcelain and Phenolic Lampholders
Pony Cleat Type                           Dimensions in inches
DESCRIPTION             CAT #    RATING      OD     OH       C
Candelabra Base Plastic 10028  75W 125V  1 7/16    7/8    11/8
Miniature Base, Plastic 10020  75W 125V  1 5/16    7/8   31/32
Medium Base, Phenolic    9063 660W 250V  1  7/8  1 1/2  1 5/16
Medium Base, Porcelain  19062 660W 250V  1  7/8  1 1/2  1 5/16

    Leviton 9063
    A word about using a light bulb as a current limiter. If you measure a 100 watt light bulb with an ohm meter, you read about ten ohms, and if the bulb were to stay at ten ohms, when plugged in, it would draw 1440 watts! Cold filament resistance is much less than when it is hot, which makes it much more like a wire when it is cold, but still is useful as a current limiting device. I re-iterate this here, because I have some very interesting formulas that allow you to calculate things like the actual bulb life you will get if you operate the bulb on less than it's design voltage, or what resistance its filament will provide at differing voltages, and so forth. 
    -------------------------------------------
                                           
Components needed for this experiment:     
                                           
An inclosed internal cabinet wiring type   
   120V light socket, eg. it should look   
   like the one in the illustration above  
   Leviton Corp. Catalog number 9063       
                                           
100 watt 120 volt light bulb               
A 2 or 3 amp fuse that fits in light socket
C1 - 1.0 microfarad 250 volt capacitor     
     1.5 microfarad 600 v will also work   
R1 - 3000 ohm 3 watt potentiometer         
     3500 ohm 5 w will also work           
1.0  amp 200 volt Diode bridge             
     4.0 amp at 600 v will also work       
                                           
Ancillary materials:                       
Wood screws for fastening the light socket 
20, approx 1 inch long, flat head nails    
10" by 15" by 1" thick piece of plywood    
Some hookup wire                           
Some Alligator Clip Leads                  
One assembled and tested Suicide Cord      
A good reliable VOM (multimeter)           
A sturdy worktable with an insulated top   
A heavy duty extension cord                
                                           
-------------------------------------------
    Ok so wire it up, and use the red link wire, shown in the Resistance versus Reactance diagram connecting the light bulb to the capacitor, omitting the link wire shown in blue, that one is for the second half of the experiment. The red, and blue links are, in reality, most likely, going to use the same alligator clip lead, in both halves of the experiment, the only difference being that in one, the clip is connected to the capacitor, and in the second half it is connected to the potentiometer.

    It is standard industry jargon to refer to capacitors as caps, and potentiometers as pots. I will at some point dispense with the long form, and so I air this now to avoid confusion later.

    Now look at your breadboard, and imagine what you would do when you unclip the alligator clip from the capacitor, and connect it to the potentiometer. There are three terminals on the potentiometer, this experiment uses only two of them, the choice you make of which of the two remaining terminals to use determines whither clockwise, or counterclockwise rotation of the pots control shaft causes the resistance of the pot to increase or decrease. Put in other words, if you connect say the middle terminal, and the left terminal to the ohm meter and start turning the knob for maximum resistance, if you then were to connect the meter to the middle and right terminal you would see nearly zero ohms. As a critical step in the preparation of this experiment you need to mark, read this get out your sharpie, or magic marker, and some how draw arrows near the pot, pointing to the terminal you intend to connect the clip lead to, when the second half of the experiment is performed, and draw an arrow that indicates which direction the knob needs to be rotated to achieve maximum resistance for your chosen clip lead connection. As the final step dial it to maximum resistance, and be sure you know that you are reading the resistance scale, they are usually ordered in the reverse of all the other scales. If you get this wrong, you will likely burn out your meter, later when you go to do the second phase of this experiment.

    A word of caution: If you have selected the Range Doubled 43 Range Multitester that Radio Shack puts on sale from time to time, I mention this one because I have information on it, the zero ohm current at the probes of the meter, when set to Rx1000 is 0.125 ma, and at Rx100 = 1.25 ma and at Rx10 = 12.5 ma and at Rx1 = it's a whopping one eighth of an amp! I'm about to show you an extreme however very common example, of how destructive a simple ohm meter can be to components you might want to measure. Let's say you have a one megohm, half watt pot, and you dial it all they way down to as low a resistance as you can get, you'd be lucky to get it down to 50 ohms, ok so 50 it is. The formula for power is P=(I^2)*R if you know the full scale zero ohm current, you can read the current directly off the dial of the multimeter, by reading a scale of that range. In this instance 50 ohms, at a scale setting of Rx1 draws 20 ma, and 0.020 squared is 0.0004 times 50 ohm is 0.02 or 20 milliwatt. That doesn't sound like much, but just wait till you see what it's going into. The one megohm half watt pot, is dialed down to 50 ohm, thus only fifty millionths of the carbon resistance element is available for dissipation of power. Since the whole pot is a half watt pot, the active area of the resistance element is only capable of 25 microwatt, and the power the ohm meter is applying to the poor defenseless little pot, is nearly a thousand times greater! Can you say poof. In truth it would take Hollywood Pyrotechnics to produce anything visible, however this does indeed damage the pot. The damage manifests itself as erratic operation near the damaged end, as the wiper arm makes intermittent contact with that area of the resistance material that has been scorched.

    A little common sense here is required, measure the far two terminals of the pot if you don't already know how many ohms it is Stop to Stop. Then if you want to measure the wiper arm through the resistance element to the end terminal, with your handy VOM, if while measuring the resistance of a pot, as high as 2.5 megohms, should you have this uncontrollable urge to dial it down to zero, use the Rx100 scale. I give you a table of ohmmeter range settings that should not be too destructive for the short duration of time it takes to make a reading. These guide lines at their extremes, stress the pot at a rate four times the pot's wattage rating, but all the heat is concentrated in such a small area, that it will most likely dissipate without doing any noticeable permanent damage. Remember the Range Setting shown is the lowest range setting that you should be using for a pot with less than or equal to a full Stop to Stop resistance, shown in the chart, and of a given wattage greater than or equal that shown in the chart.

    -------------------------------------------
1 Watt Pots   1/4 Watt Pots   Range setting
                                           
ridiculous    250 meg         Rx1000       
10 meg        2.5 meg         Rx100        
100 k          25 k           Rx10         
1 k           250 ohm         Rx1          
-------------------------------------------
    These guide lines are loosely based on the aforementioned meter, loosely in that, I try to take into account that the small size of the energy dissipating region of the resistance element, will more readily carry heat off from the affected area. Additionally the fact that maximum power transfer occurs at fifty percent of the Thevinized voltage, or if you prefer Nortonized current of the ohm meter's output. Thus the meter is at half scale when maximum power transfer occurs, and on these meters, this point on the dial is ten on the ohms scale, thus 10 ohms draws 62.5 ma on Rx1 dissipating 39 mw, 100 ohms draws 6.25 ma on Rx10 dissipating 3.9 mw, and soforth, here's a table. 
    -------------------------------------------
Range         Resistance      Power        
Rx1               10 ohm       39 milliwatt
Rx10             100 ohm      3.9 milliwatt
Rx100           1000 ohm      390 microwatt
Rx1000         10000 ohm       39 microwatt
-------------------------------------------
    Electrical Safety note:
    Use the same kind of procedure you used for checking metal surfaces of the of the Suicide Cord's Control box, to check to make sure that any metal surfaces you need to touch are not electrically connected to any of the wiring. Especially the control shaft of the pot, because you need to turn this while power is applied, in the second half of the experiment. Also test the metal body parts, and if they show conductivity, make a mental not to touch them while the circuit is powered up. Just as important is to know what portions are insulated, because part of what you will be doing is feeling it for signs of heat, eg. increase in temperature of about 20 Fahrenheit degrees, and you should know what is safe to touch, before you get to that stage.
    Contemplating the cosmic one-ness of the above experiment.
    Ramifications:
    As the experiment clearly demonstrates, a pure reactance does not dissipate, or use energy, so you might wonder since it is drawing current, but not power, can I draw current without spinning my electric meter. The surprising answer to this question is yes! Electric meters are designed to measure true power, and since a reactive load does not dissipate, or use power, they don't register on an electric meter. That said, nothing is free, there is a price for all of this, current is being drawn after all. So who pays? The electric power utility, that's who. The additional current that your little reactive load presented to the AC powerline, resulted in additional current flowing through the transmission lines that ferry the power to your house. That additional current passing through copper wires, that have resistance, is converted to heat, and does require power.

    The irony is not lost on Electric Utilities, they offer discount incentive programs to major industrial users of electricity, in exchange for their cooperation in maintaining balanced power factor loading on the powerlines. It doesn't stop there, in Europe, and some other parts of the world, and someday soon even in the US, laws are being passed that require balanced power factor loading on any household appliance sold, above a certain wattage rating. The wattage rating varies, from country to country, and is reduced over time as technology improves the cost/benefit ratio, currently my understanding is that some European markets require this on 50 watts or more, but don't quote me on this, if you intend to design an apparatus for such a market, check their laws, and get information on regulations still in committee before finalizing your design, because by the time you gear up for production you will probably be required to comply with laws, that at the time you asked, were only a gleam in a law makers eye.

    None of these laws apply to a one of a kind prototype apparatus, such a law would stifle innovation, and be utterly unenforceable, many governing bodies have tried to pass such laws in the past, and most have learned by experience that unless a law has the backing of the large majority of the people, and is technically capable of producing the desired result, it is ultimately repealed, and all the expense trying to force the impossible to work, is thrown away, a total loss. Law makers are believe it or not, even in dictatorships, sensitive to these realities, they in some cases in a face saving move, such as the failed "", turn a blind eye to these realities until such time that there is a consensus for change. I am a guarded optimist, in the future we can hope these governing bodies will take seriously the information that science provides, without paying science to cook the results. Even middle managers can screw things up though, Space Shuttle Challenger, and the Hubble Telescope were avoidable, if only the middle managers would have listened. You have a duty to make them understand, if you ever find yourself in such a position, exercise it, because you can't undo tomorrow what you fail to correct today, and it will haunt you for the rest of your life.

    I actually performed this experiment with two capacitors that I had on hand with suitably high voltage, a 1.0 uf, and a 3.3 uf, both at 250 wvdc (working volts direct current) and I used the measured current to calculate the actual capacitance of them. Here is the results of that experiment. Oh and one other little detail, a non-polarized cap that is rated xx volts DC doesn't mean that you can't put AC across it, it just means that you have to consider the "peak" voltage of the AC you are applying to the cap, specifically if it is a sine wave, multiply the RMS AC voltage by 1.414 as you learned in lesson 010, the lesson on Sine Waves. 
    -------------------------------------------
I measured 48 ma with the 1.0 uf           
120 / .048 = 2500 ohm Xc                   
1 / 2 Pi 2500 60 = 1.06 uf                 
                                           
140 ma with 3.3 uf                         
120 / .140 = 857 ohm Xc                    
1 / 2 Pi 857 60 = 3.09 uf                  
-------------------------------------------
  • 014_HV_bred_bord_4.mp3 Audio discussion of high voltage breadboarding 4.07 meg

    • You may be wondering what the pot is doing in this circuit, the profound answer to that question is nothing. But you say, it is shown soldered to a wire and the 100 ohm resistor. Ok, not nothing, the pot's middle wire is simply serving as a securely anchored terminal, but the pot itself is not really part of the circuit, it's just a handy anchor point, oh and by the way, don't forget to remove the grey wire that was there before the resistor was installed in it's place, in other words, snip out the grey wire that previously was connecting the 1.0 uf cap, and the wiper arm of the pot.

    Identifying windings of an unknown transformer
    This subject is one of those things that when the pieces all fall into place everything makes sense, and prior to doing that it appears to be a black art. To really understand how to properly categorize an unknown transformer, you need to think like the guy that designed it, and to do that requires a rudimentary understanding of what tradeoffs are considered in such a design. So bear with me, this will get a little strange. If you apply a small AC voltage to one of the windings of a transformer, all of the other windings will present at their various turns ratios, voltages that are ratiometric to the input voltage you have applied to that one winding you are temporarily using for a primary winding. Remember there really is no such thing as a primary, and secondary winding, in a transformer in any absolute sense, rather the geometry, or if you prefer the "bobbin window area" is divided up to optimize for maximum power transfer, and using a secondary winding, as a primary, has little effect on the transformers over all effectiveness, unless it has a multiple secondary windings. Why? The designer of a multiple winding transformer must set aside half of the available window area for putting power into the transformer, the remainder if it is a simple two winding transformer, will be a winding that is used to pull power out of the transformer, a two winding transformer, read that, one primary, and one secondary will operate equally effectively in either direction. However if it is a transformer with two or more secondaries, say three by way of example, what you have is three secondaries sharing the other half of the available window area
    In truth careful transformer design tries to take into consideration the fact that layers of insulation use up window area, this is especially true of multi winding transformers. So much so that a transformer with ten windings has only about half the power output of a two winding transformer of the same size and weight. Then there is the matter of wire resistance, since there is more wire per turn the farther out you get from the center of the transformer's core, the more electrical resistance you have in the copper windings the farther out you get from the center. It would be a poor design indeed if this were overlooked. A transformer not given attention to this detail, is likely to be very lopsided, for instance, an isolation transformer, if designed properly should have equal DC coil resistance on both primary, and secondary. In fact if designed right, you should not be able to distinguish between the primary, and secondary by any DC or low frequency measurement you could make external to the transformer. So how would a transformer designer go about getting the resistances to match in an isolation transformer? The answer is, you would use smaller diameter wire on the primary, because that winding is shorter. The smaller diameter wire has more resistance than a larger diameter, but, being shorter compensates. Then after it is wound, the secondary is wound on top of it. The secondary is longer, even though it has exactly the same number of turns as the primary. The added length means more copper wire, and more resistance, but the fact that we are compensating by using larger diameter, eg. lower resistance per linear unit wire, with any luck the two windings resistances match perfectly. In practice luck has nothing to do with it, there are a series mathematical formulas that determine what wire size to use to place the transformer in proper balance. These formulas result in primaries that occupy considerably less than half of the available window area as a practical matter, but as a first approximation, the notion of the primary occupying the first half of the window is more easily understood

    Transformers in the wild vary widely, from one sub species to another. If you ever see a transformer with a primary rated 120 volts, at 60 hertz only, this is a transformer wound to run well into the saturation curve, and it will idle hot, compared to it's international 50/60 hertz counterpart. By idle, I mean power is applied to the primary, without any load connected to any of the secondaries. A transformer rated at a given voltage, for 50/60 hertz, means that it will run on either frequency, obviously if you run it at the lower frequency it will run right at the onset of saturation, but if you live in a 60 hertz country you will never see 50 hertz, and if the need arises you can get an additional 15 to 20 percent more voltage out of such a transformer, by running at a little higher input voltage, or setting the tap to a lower value. If you do this it will idle about as hot as it would if it were running on European, or Japanese 50 hertz current using its normal design voltage.

    Caution:
    Idle any transformer you intend to do this to, for four hours, to allow it to reach thermal equilibrium, before you wire it up permanently. And while waiting for it to stabilize, touch the frame of the transformer under test, every minute for the first five minutes, then once every five minutes for the next half hour, then once every fifteen minutes for the next hour, and then once every hour there after until you are sure it has gotten as hot as it's going to get. It should get no hotter than a temperature that you can comfortably hold your finger in contact with the frame for ten seconds. If it gets hotter than that, you're pushing it too hard, back off on the input voltage just a little, or set the input tap up one voltage above the present setting. I show below a circuit to measure the current waveform of a fairly large transformer running at the onset of saturation, followed by the actual waveform itself.

    In the above waveform the variac is adjusted such that the meter reads 120 volts and the voltage plotted in the waveform is an indication of the current flowing through the transformers primary, in that it is a measurement of voltage drop across a series current sensing 30 ohm shunt resistor. Thus from one millisecond to the next the current flowing through the coil of the transformer's primary winding is charted on the Velleman Hand held Liquid Crystal Display Oscilloscope. The Velleman has several advantages over conventional oscilloscopes, plus a few draw backs. The main advantage here is that I can plug the Velleman into the serial port, set the port to 9600 baud, and the computer can read the waveform, as a list of points, that various Math Visualizing programs can output as a dot png file that your web browser can properly display. Another advantage is that it is battery powered, while the actual measurement is taking place, thus there is no possibility of a ground loop, that poses a danger to both men/women and especially machine. I provide more on the Velleman K7105 Scope should you require such info.

    Notice that the waveform is anything but linear, a linear current waveform would look sinusoidal, this one is anything but.

    The next circuit is a variation on this one, I setup a DC power source that can pump an average of 500 ma. into a 25 volt RMS secondary. The DC power is composed of a smaller, I.E. lower voltage variac, that provides a controllable AC voltage to a diode bridge, capacitor combination. The capacitor is suitably large, such that it's impedance, or RC time constant with respect to the resistor, is negligible. For our purposes it behaves like a variable battery. The current from the variable battery is limited by the series 50 ohm resistor, and I show the saturation waveforms for both, where in case one, the variable battery is set to zero volts, but still connected to the secondary through the 50 ohm resistor. And case number two, where I actually pump the transformer's secondary with an average of 500 ma. The result is a non-symmetrical saturation curve, shown in blue superimposed over case one the reference wave shone in red. The reason the DC powersupply and current limiting resistor remain connected during the reference phase of the test, is to establish the primary current waveform while the secondary winding is being loaded by the 50 ohm resistor, failing to do this would introduce additional variables into the experiment, when we went to the phase two, where we actually pump the secondary winding with polarizing direct current.
    Not to spend a lot of time on this, but earlier I mentioned the curiosity of Polarized Inductors this experiment demonstrates the phenomenon, by placing a direct current on one of the windings of a transformer, that is otherwise being used as an inductor driven to the onset of saturation. The direct current flowing in the secondary, replaces the permanent magnet in the Polarized Inductor and illustrates the point that coils are not so different from one another, in that they're behavior can be coaxed into doing many specialized duties. A variation of this phenomenon is the heart of a flux gate magnetometer. Oh there I've gone and done it, straying way off the path, Ok back to identifying Wild transformers.

    Ok now let's say you have a transformer of unknown origin, you can't even be sure if it is intended to be powered off the line voltage. Well the first thing you do is to ohm it out to see what paths of current flow between the lead wires, or terminals of this undomesticated transformer. Draw a diagram of the paths of electrical continuity, and write down their DC resistances. As a final check test to make sure that there isn't a path of conductivity you may have missed, remember often transformer windings have many taps. If you encounter a single wire that appears not to be connected to anything note this one with suspicion, it could be an interwinding shield or maybe an open winding, most likely a burned out transformer. If you encounter two such terminals, it is almost a certainty that it is a fried transformer. If the transformer is fried, mark it as bad, and go on to the next one.

    Using an AC wall wart that produces six volts AC, power one of the medium resistance windings of the undomesticated transformer. Measure the six volt AC with and without the load of the undomesticated transformer's winding loading the wall wart. If it droops below four volts AC, try another winding of the undomesticated transformer. Now with the undomesticated transformer winding connected to the six volt AC source carefully measure the other windings of the undomesticated transformer, and write their respective voltages down on your diagram. Do this carefully, an undomesticated transformer can do anything turns ratio wise, it could boost that six volt input up to hundreds of volts on one of the other windings, so treat them as dangerous, until you have measured them, and know that they are not.

    One way to gain experience with this phase of the procedure is to carry out this procedure on a transformer that you really do in fact have data on, as a dry run. Doing a dry run, is also useful at several other phases of this procedure, that I have not discussed yet, so remember this if you have any doubt about how to carry out one of the other phases of this procedure.

    When you figure out the voltages of all of the other windings, with respect to the one winding you are pumping with six volts AC, what you have is a crude map of the turns ratios. If you have reason to believe this transformer was a multi winding step down transformer, there will be one winding that appears to have the highest AC voltage, when compared to all the others, and it is likely that, that winding is the power input winding. If that windings lead wires exit the transformer from the opposite side of the transformer, from all the other wires, the likelihood is even higher. If the lead wires are color coded, and the wires you suspect from your measurements are the power mains, eg the primary winding of a line power transformer, and those suspected wires are either black, or white, or some striped combination of black, and white then it is a near certainty, that you have located the power mains, of what is a line power transformer. On the other hand, if this transformer is known to have been removed from Vacuum Tube equipment, including Tube based Laser, high power Microwave, such as Cavity Magnetron drivers, Neon Sign transformers, old Oscilloscopes, that don't use a modern solid state flyback design, etc. the highest voltage winding will likely NOT be the power input mains. For this reason it is important if you are about to salvage a transformer from a piece of equipment, to note which wires were connected to the powerline, before you go cutting wires, and since the output voltages of the secondaries usually go to diode bridge assemblies, whose DC output goes to a filter capacitor, it will save you enormous effort if you note the voltages marked on those, filter caps, and draw a little diagram of what winding they were connected to, before you pull the transformer out. Cost containment prevents manufacturers from placing radically higher voltage capacitors in a circuit than are necessary, although they are often a third higher voltage, than is actually applied, to allow for a safety margin in the event of overvoltage operation, and voltage surges. Oh and a word of caution, especially on high voltage equipment, if you suspect the unit has been powered up recently, go in with an insulated handled screwdriver, and touch the blade across, the terminals of all of the capacitors in the system, in other words short them all out, before you get in there with your bare hands. Capacitors can recharge on their own by a process known as Dielectric Charge Migration, essentially a discharged cap can have regions within its dielectric that each contain charges that neutralize each other, and if one leaks off, the cap assumes the difference charge. While probably not terribly dangerous, it might not be very pleasant. Also Tube based equipment is these days getting to be rather scarce, so a transformer culled from such a piece of equipment is a very valuable find. You won't often need high voltage, but when you do there simply is no substitute for the good old transformer you culled from that TV set you found in the attic last summer. Ok we will assume you have figured out what you believe to be are the power mains of this as yet undomesticated transformer. At this point you can if you want play with the ratios arithmetically, to derive the actual voltages that will be present on each of the secondaries, assuming you are right about the selection for the power mains. In fact the ratiometric derived secondary voltages, will not be right on the button, but they will probably be fairly close. Ok now connect up your undomesticated transformer, to the bread board, using the light socket as a current limiter.
    You need at your ready disposal an assortment of different wattage 120 volt light bulbs, to make these tests. The bulbs you should choose for this purpose should be transparent if at all possible, as you will be looking for a dim glowing filament, as opposed to a brightly lit bulb, also useful is an adaptor socket that screws into a normal one inch light socket, and accepts the kind of bulb that you find in standard 7 1/2 watt, and 4 watt night lights to extend your range down to those lower currents. To be able to convey the transformer size and their attendant 120 volt primary characteristics, several options are available to me. I could have used weight, but that would have required people reading this page to have on hand a scale that reads accurately in the range of a few ounces, to ten or fifteen pounds. I could have used volume, but transformers are irregularly shaped objects that would make it hard for readers of this page to compute the volume of transformers. I choose a simple, and concise standard, that is accurate enough for the kind of thing we are trying to get across. My concise approximation amounts to this, imagine the smallest empty box, with regular right angled sides, that the transformer will fit inside of. You don't need the box to actually fit your transformer into, just a picture in your mind of such a box. Now measure the transformer as if you were going to order a custom made box, that would fit your transformer, like the glove fits the hand. You'll need three measurements to accomplish this. Now solve for the volume of that box. To do this one simply multiplies all three dimensions together. I will refer to this volume as the Transformer Package Volume, or the abbreviated form TPV. Do not include the mounting ears, terminals, or lead wires in these measurements, I'm trying here to find a simple uniform way, we; you, and I, can reference the meat of the transformer. For example I have a transformer, the coil of which is wound on an exposed plastic bobbin, that is pretty much filled with windings. the distance measured across the bobbin is 1.8" and the dimensions of the magnetic core laminations are 2.2" by 2.7" so I claim this transformer has a TPV of 10.692 I show a table below in which I list this transformer as the first case study, and in the table the first and second column show the size of the lamp screwed into the light socket, and the actual voltage read across the lamp, followed by my TPV specification, the transformers VA rating as defined by a thing known as the ten percent rule, and lastly the frequency the transformer is designed to operate at. 
    -------------------------------------------
       Lamp        TPV     VA     Frequency
-------------------------------------------
 25 watt  20 volt  10.7    50.4   60 hz    
 25 watt  16 volt  37.7   140.0   50 hz    
 25 watt  18 volt  37.8   -----   50 hz    
100 watt   5 volt  90.0           60 hz    
                                           
-------------------------------------------
    The VA rating, and the ten percent rule:
    To compute the transformers VA rating, this means essentially the wattage capacity of the transformer, using the ten percent rule, requires you to have already ascertained which winding power is to be applied to, and what voltage it is designed to be powered with. If you decide that this is indeed a transformer designed to operate on 120 volts AC, unscrew the light bulb, and replace it with one of those three ampere fuses that I mentioned earlier. Now with it running you can make more accurate voltage measurements of the secondary windings idling, that is not powering any load. You need to know the voltage of each of the secondaries if they're are more than one, and you also need to have a large Rheostat, Potentiometer, or switchable load bank, to load the transformer down with. The reason I say large Rheostat, or Potentiometer, etc is that these resistors will be sucking perhaps hundreds of watts for just long enough to measure the droop in output voltage the transformer is delivering. You adjust the load bank, so that when connected to the transformer it loads the transformer's output voltage down to 90% of its unloaded voltage, a droop of ten percent, hence the ten percent rule. If you know the resistance of your load bank, and the voltage of the secondary winding at the time the load was pulling down on it, you can use Ohms Law to compute the current. Knowing the current, and the voltage, you can compute VA, eg. Volts times Amperes, and for most purposes thats the same thing as Watts. A single secondary transformer is fairly straight forward, the fun comes when trying to categorize the VA rating of a multiple secondary transformer. For now I will say only that is beyond the scope of this lab explanation, and that it involves a Thevinin approach to the problem. Ok I'll elaborate a little, upon finding a transformer in the wild you know nothing about what its designer's priorities were. As an extreme example, imagine a transformer designed as an isolation transformer with an additional small low voltage winding intended to drive a small piece of electronics that was to act as an Electronic Circuit Breaker a device that pulls the lever in a relay to open the contacts of the powerful secondary winding, thus functioning as a Circuit Breaker, with one additional very nice feature, it has a knob to allow you to control the sensitivity of the Circuit Breaker. Thus you can dial in any current from a few milliamperes to the maximum the isolation secondary can withstand, maybe five or ten amperes. Such a transformer has a very lopsided set of resource allocations with respect to how the VA ratings of the respective secondary windings are designed. Now contrast that to a transformer that the VA ratings of the secondary windings more or less evenly divided up, and you start to appreciate the complexity of this problem. Once again the ten percent rule can be easily applied to get you a concise answer. The technique is to apply the ten percent rule to each winding individually, while measuring the open terminal voltage of one of the other windings, both with, and without the load applied to the winding undergoing the ten percent rule power check. Doing this you will likely find one winding, that sucks considerably more power, than the others, and you will also gather a feel for the major runner up. Now back off a little on the loading of the major winding, to allow the runner up to perform about 80% or 90%, of its ten percent rule loading and try combining the two loads to see if you can get a total load of both windings to as an aggregate, load the transformer as a whole according to the ten percent rule. Likely the other windings are so small by comparison that bringing their loads online, won't severely overload the primary. To put all of this in context, a transformer idling will be anywhere from 100 Deg F to 110 Deg F depending on how deeply it is driven into saturation. When the load is applied at the level called out by the ten percent rule, the temperature will rise another 50 Fahrenheit degrees or so. Transformers can tolerate at the extreme, a temperature of 180 Deg F indefinitely, however this leaves no margin whatever for voltage fluctuations, so you never push one this hard without providing adequate cooling. As you can see you have quite a bit of wiggle room when assigning VA ratings of secondary windings, and when in doubt you can always under specify, eg. err on the safe side.
    Phasing your transformer:
    In the drawing below I show the example transformer wired up such that all voltages add. I have also included phase dots on each winding, if you connect up a transformer this way, and one of the windings seem to subtract instead of adding to the voltage, that winding's terminals, or wires are backwards, and if you reverse those two wires they will add voltage. When you get done they all should add. Once this is done, you can mark them some how, examples of marking them, are, tying a loose simple knot in the phase doted wire, nicking the end of the wire with a pair of side cutters, or judicious use of a modern felt tip pen.
    It should be obvious by now that terminals 2, and 3, are in fact the same terminal, as configured above, I just thought I'd mention that, if this didn't automatically occur to you, it should have, you've missed something critical along the way, go back and review some of the early lessons. Anyway Terminal 3 should be 120 volts with respect to ground, your line voltage may not be exactly 120 so don't fret if it's within 10%. Terminal 4 should be higher by the voltage of the first secondary, terminal 5 should be higher by the voltage of the second secondary, and finally terminal 6 should be still higher by the voltage of the third secondary. If your transformer has one of the windings reversed you can fix it, and go on. Once you get them all in phase, that is so that they all add, power the whole thing down, leaving the wires of the transformer windings connected to each other, and carry the transformer to the workarea where you intend to mark the wires.
    Next I show a simple Half Wave rectifier, and simple single capacitor filter circuit, with some provision for measuring the current waveform, carried by the diode. What is ofcourse being measured is voltage drop across the 0.3 ohm current sensing shunt resistor. The following frame I show actual waveforms taken by the Velleman K7105 handheld oscilloscope. Notice how, as the current waveform reaches maximum, the input voltage delivered by the transformer, shown here in Red is severely flattened by the nonlinear current drawn by the diode, and then on the negative half cycle, the transformer, nolonger subjected to the diode's load, is free to produce almost two more volts. Also observe how, as the Red positive peak forward biases the diode, only as it exceeds the cap voltage by the diode drop, does any energy get transferred to the cap to replenish its charge. This is by contrast a very brief period of time, this time slice is so short, that to accomplish the charge replenishment, almost 1 1/4 amps flow in that brief period of time, into a cap, that is only providing 240 milliamps of current to the load. Rectifier diodes are routinely subjected to very high repetitive pulses of current, many times the design load current. Any series resistance, in either the cap, or the transformer has considerable impact on the amount of power such a power supply can deliver.
    Both the Red transformer voltage waveform, and the Green capacitor voltage waveform are measured at the same scale setting, the Blue current waveform, is in reality a tiny voltage measured across a current shunt, and would therefore be inappropriate to set at such an insensitive scale setting. All of these however are referenced to the same zero reference to make easier the interpretation of this first waveform on the part of the student. Notice that the Green capacitor waveform has so little activity that much of the detail is lost. In the next set of waveforms I suppress the zero and rescale the Green capacitor waveform when I cover Full wave rectification, because without this technique the 'Y' axis movement is a mere single pixel. I mention this here so as to warn you not to be complacent about zero suppression.

    These are real waveforms, not textbook drawings, and some unanticipated phenomena needs perhaps an educated guess as to the causes. First you would expect that the capacitor voltage waveform would follow the transformer output into the circuit by 7 tenths of a volt, but it follows by more like a volt and a half, why? These voltage measurements were made one at a time, and then pasted together into a composite, it is possible that the powerline voltage fluctuated a little, or I may have absent mindedly made the measurement with the current sense resistor still in the circuit while I made the measurement, but even including that 0.374 volts still fails to account for the discrepancy, so I say a combination of factors, wire resistance of the cheap "Radio Shack" clip leads, line voltage fluctuations between measurements, and measuring cap voltage while the current shunt was still in circuit all came together to produce this anomaly.

    Another anomaly is the fact that the bottom half cycle, of the Red transformer output voltage is not as round as it seems it should be I assume this is some of the compound saturation effects of the test setup I used, an isolation transformer drives a Variac, it drives the transformer shown, which is exhibiting a slightly less than sinusoidal negative half cycle.

    Third I need to mention that all of these waveforms were phased, that is aligned to each other with respect to time after the measurements were taken, in the Grace math package, using Emacs macros to do the alignment. I hope I got them right :-)

    Ok on to the Full wave rectifier circuit.
    Like I told you, the Green cap voltage waveform is zero suppressed this gives me a way to provide you more detail than would otherwise be possible. Notice that the Blue current waveform is only a little more than half the magnitude, of its Half Wave counterpart, still delivering the same output. This happens because it occurs twice as often, if you missed this, study the two waveform sets, comparing them to each other. Showing the Green current waveform in this kind of detail, allows you to see why they call this sort of waveform a Ripple Wave, again the short rise time that is the charge cycle, is in contrast to the relatively slow fall, or discharge time. RC Time Constants describe the discharge portion of the wave, and therefore the magnitude of the ripple. In normal powersupply design you want as little ripple as possible, on the other hand an infinitely large cap is also infinitely expensive, and infinitely heavy. not to mention large as the universe. So you have to make some tradeoffs. Also the smaller your ripple voltage, the more severe the exaggeration of the diode doing all the work in an ever thiner sliver of time.

    The information I've given you concerning time constants, RC discharge characteristics, and the like is all that you really need to design such powersupplies to a second approximation. There are formulas for many standard configurations, you might be tempted to acquire some of them, but you really don't need them, and few who memorize them remember them ten years on. So I don't make a big deal about them, the Internet is vast, if you think I should drop some pointers, drop me a line, and I'll consider it.

    Analog series pass transistor based regulators present a Constant Current load to the filter cap, and switch mode regulators present a Constant Power load to the filter cap. These various types of load make very little difference to the curve, or the way you calculate the size of the cap if your ripple is small, eg. less than ten percent. My first approximation treats the load as if it were a constant current, and usually that's all that's necessary. Line noise, variations in temperature, and component tolerances, all factor in to cause far greater error than the miniscule error caused by using the wrong current curve model. So the first approximation Rule of thumb is to simply use the relationship of one Ampere of discharge current, flowing out of a one Farad cap, steadily reduces its voltage by one Volt per Second. To keep the proportions straight in your mind reducing the discharge current slows the voltage decent, and reducing the capacitance speeds up the voltage decent, in linear proportion.

    Some texts take up weeks of your time on the above subject, and when you try to apply all the theory in the lab you discover the fine points the theory makes can't even be measured because of all the noise factors. I have given you a simple practical way to compute the size of the cap that's hard to beat. I'm not discouraging you if you want to know the details, as I said before the Internet is a big place, go for it.

    Some interesting rectifier configurations:

    At this point I will assume you've tried a few of the things I've put forth as experiments, the next section will detail some arrangements of diodes, and capacitors, that produce useful unregulated DC power supplies.
    The above power supply produces two voltages from the same transformer, plus a handy full wave signal that can be used for detecting Zero Cross. Both of the DC voltages, are full wave rectified sine waves fed into the filter cap and as such require considerably less filtration, eg. capacitance. The bottom half conditions the signal into a short pulse for timing things that rely on things that coincide with the 60 hz beat of the powerline, a very precise timebase.

    To understand how this circuit works, momentarily ignore the top two diodes and, the cap that they charge, also ignore everything below the bottom diode. What you have left is a simple two diode full wave rectifier, that has a seemingly useless, but relatively harmless third diode, the bottom one, charging the cap that drives the 12 volt supply. Now add in the resistors and transistor, and the significance of that third diode suddenly has relevance. That third diode blocks the charge on the cap, from propping up the voltage across the bottom resistor during the period when the AC sinusoid is not at maximum, thus the bottom resistor has a textbook picturesque full wave rectified sinewave across it. The middle resistor converts this waveform into current that drives the base of the transistor and since the transistor's beta factor, a measure of it's current amplification capability is on the order of 100, and since the transistor's base emitter junction, behaves like a diode, the emitter is the bottom terminal in this drawing, the transistor is biased on for all of the wave, except for the brief moment of time that the AC sinewave crosses over the zero line. The top resistor tries always to hold the output voltage at the transistor's collector terminal to the 12 volts that is always available at the cap when the circuit is powered, but since the transistor is on most of the wave, like a switch that is closed, the transistor wins this fight, and holds the voltage very close to ground potential, most of the time. The exception is ofcourse during zero cross, when the transistor's input base terminal current falls to zero. For that brief moment in time, the transistor switches off, and the collector voltage, at the whim of the top resistor, is pulled up to 12 volts DC for that brief interval.
    Now add in the top two diodes to complete the picture, and what you have there is simply a full wave bridge rectifier driven from an 18 volt RMS transformer secondary, whose peek voltage 25.45 charges the top cap to about 24 volts, after you factor in diode drop. Loading this powersupply to obtain useful amounts of current will pull down the output voltages to somewhere between 11, and 10 on the bottom cap, and 22, and 20 on the top one, depending on the applied load. Such is the case of any unloaded, unregulated powersupply. It's far from a perfect world, but even without true regulation one can make it much better.
    The right half of above circuit is what is known as a shunt regulator. The 22 volt RMS center tapped secondary will charge an unloaded cap to 14.85 volt assuming a 0.7 volt diode drop, kind'a high for some 12 volt devices, and considering powerline fluctuations this can be even worse, but even light loading can pull this voltage down considerably, such that under normal load this powersupply is right at 12 volts. The trouble is, that the unloaded cap has almost 15 volts with quite a bit of current behind it, for atleast a few milliseconds, and solidstate devices can be destroyed when subjected beyond stress limits for as little as a millisecond. What the circuit on the right does, is to, in the absents of any load, provide a small, but adequate load, enough to clamp the voltage across the cap to 12 volts + 1 diode drop, in this case the base emitter junction of the 2N3055 has the nominal seven tenths diode drop, and the 1N4742 is a 12 volt Zener Diode, a diode precisely spec'd for its Reverse Breakdown potential, in this case 12 volts.

    The good, and the bad:
    I don't really think of a shunt regulator, as any kind of a true regulator. What they do is limit the unrestrained overshoot, in other words they make great surge protectors. In the absents of any load the shunt regulator is working at it's hardest, to drain off excess voltage, but as soon as the load is switched on, the load pulls power away from the powersupply, causing it's voltage to droop, and now the shunt regulator is effectively removed from the circuit, until such time that the load is switched off. Such a scheme makes optimal use of the powersupply's output under load conditions, but in a noload situation it also wastes about a watt of power. This circuit provides a hard clamp meaning it is very responsive to spikes, due to the fact that it is usually partially on, that is the 2N3055 is usually partially conducting, and thus more ready to respond to variations in voltage. Placing a carefully chosen resistor across the Zener diode can trickle just enough current even at load conditions to insure this added responsiveness. 1300 ohms might be a good starting point for such a resistor, and if it were a pot, you can tune for minimum smoke :-) the idea here is not to alter the functionality of the circuit as a whole, rather you adjust the pot to the point where it just bearly begins to affect the unloaded voltage, and then back off just a smidgen.

    I show the circuit being powered by a 22 volt center tapped secondary followed by two diodes, another viable configuration is to use a 12 volt non-tapped secondary, and a four diode full wave bridge rectifier to feed the cap, this is roughly equivalent, inspite of the somewhat higher voltage, eg. a 22 volt center tapped winding develops a peak voltage of 15.55 on each leg and has one diode drop, where as a 12 volt secondary produces a peak voltage of 16.97, and has two diode drops in a full bridge rectifier. To contrast the unloaded theoretical voltages of these two schemes, we get 15.57 volts for the 12 volt bridge rect version, and 14.85 volts for the center tapped 22 volt version. Only about a diode drop of difference between the two schemes, thus if you were real particular, you could add an additional diode to the 12 volt non-tapped version if you really wanted it to behave identically to its 22 VCT counterpart.
    In the above circuit I show a clever configuration, of an almost, but not quite, full wave bridge rectifier. This modification of a bridge rect. provides two independent loads, that operate in the same polarity, power that has nearly zero interaction from the neighboring load. In other words if one load's current fluctuates, as a result of circuits switching on and off, the voltage of the other load remains steady. This is not the quite the same thing as regulation, if the AC line voltages fluctuates, both supplies are affected. Often you are designing circuits that have very sensitive amplifiers in one section, that control massive amounts of power elsewhere in the circuit, it can be an incredibly daunting task to keep power perturbations in the output stages, from causing the sensitive input stages to react to them, thus causing a feedback loop that oscillates at the total loop delay period. The way this circuit works is it charges one cap on the positive half cycle of the transformer, and the other cap on the negative half cycle. On the down side, both power supplies, in achieving independence from each other, are no longer full wave rectified, they are only half wave rectified, thus they require much larger caps to achieve proper filtration.
    This non-isolated powersupply has a switch at the bottom that changes the voltage produced by the supply. Plugged into 120 volts, with the switch open the diode bridge rectifies the AC voltage and places the result across the two series capacitors, the resistors are there to insure the voltage across the two is equal. Measured from the minus DC to the plus DC you would read about 170 volts, no surprise, Ok now close the switch, suddenly the output voltage jumps to double, 340 volts! Why? The switch bypasses the two diodes it is directly connected to, changing the circuit from a fullwave rectifier bridge, to two DC halfwave powersupplies wired in series in additive fashion. In the configuration with the switch closed, the the only two diodes that have any effect are the top diode, and the second from the bottom, the others remain reverse biased at all times. While this is a pretty slick circuit, a clever way to get two different voltages out of the same supply, that is not how it is used. The voltage selector switch on the back of your computer's powersupply is wired exactly the same way. It is set switched open, for operation on an electrical outlet that delivers 240 volts AC, and it is switched to the closed position for operation on 120 volts AC service, thus making it capable of operating on both domestic, and foreign electric service, and assuming the switch is set properly, it delivers the same DC voltage to the electronics in either case.
    Here's a way to arrive at a pair of plus, and minus fullwave rectified DC powersupplies, where the negative supply, in this case, is not required to deliver very much current. The two 200uf caps to the left of the diode bridges are employed to shift the AC sine wave by an offset equal to the peak voltage of that sine wave, thus still applying AC voltage to the bottom diode bridge, but shifted negative by the peak voltage value of that AC input voltage. This trick makes the input power entering the lower diode bridge appear almost as if it were coming from an isolated winding of the transformer, even though the transformer only has a single secondary winding. This kind of a powersupply is very common in external modems that are powered by a wall-wart with an AC output, usually 12 volts AC. The modem needs the plus, and minus supply voltages to be able to generate the plus, and minus 12 volt signals required by the RS232 serial signal standard that is carried by the 25 pin data connector on the back of such a modem. To further emphasize this technique of using the two caps on the left as a kind of DC isolator, I show below a version of it with a battery demonstrating the flexibility of such a design.
    The battery in the above circuit, could be any DC power source, simply shows how, by capacitively coupling the ground referenced secondaries AC signal into the DC floating lower diode bridge it now forms a separate powersupply in it's own right, floating, in this case, on top of a negative battery voltage. So you might ask, what if you put in an extra diode bridge, and a couple of diode isolator caps, like the ones on the left, and another filter like the one on the right, to replace the battery with, it seems like you would get a total negative voltage measured from the top, to the bottom most terminal on the right, of three times the peak voltage, kind'a like getting something for nothing ain't it? Well yes, and yes it would do exactly that, but all three power supplies would draw a version of their respective currents from the transformer. This gets us into the next subject, namely Voltage Doublers.
    Measured from the minus DC to the plus DC you would read about 680 volts To understand this circuit one needs to cover how it works in stages, first some reference points. Notice that the minus DC terminal is, if the power plug were polarized appropriately, at, or near earth ground potential. This fact would never be considered safe, but all hot chassis systems take this sort of thing into consideration, in much the same way as the light socket screw threads, being more exposed, are always connected to the neutral, eg. white wire. In my discussion of this circuit, all voltages, unless otherwise stated will be referenced to the minus DC terminal. To explain how this works, I will describe, each of four half cycles separately, one at a time, beginning with the line power input, the hot side of the power plug, starting at zero, and headed downward on a negative half cycle. Temporarily ignore everything but the C1, and D1, as the input voltage reaches its negative peak, C1 is charged to 170 volts. Now for purposes of understanding this circuit I want you to suspend what you know about physics for a moment, and pretend that C1 is now a 170 volt battery of infinite capacity, and zero impedance, or resistance. As the input line voltage rollercoaster rides from the bottom troff, eg. negative peak of the sine wave, back to zero, C1 acting as a battery, now dumps its 170 volts into C2 charging it to 170 volts, but as the input line voltage rollercoaster rides up to the positive peak, as it rounds the top, C2 now has a potential of 340 volts, and cycle after cycle keep biasing the diodes forward on the peaks of the waves, just enough maintain C2 at 340 volts. So now for purposes of understanding I want you to think of C2 as a battery charged to 340 volts from here on out. I now want you to think about what is happening to C3 when the the hot side of the power plug, is starting at zero, and is about to head downward on another negative half cycle. At zero volts on the hot side of the plug, C3's negative terminal is effectively connected to ground. C2 is charged up to 340 volts, and that 340 volt potential is carried by D3 also charging C3 to 340 volts, this when the input line voltage is at rest, eg. zero volts. As the roller coaster ride continues and the hot side of the powerline sweeps down to the negative peak of the wave, it further charges C3 by an additional 170 volts to a total of 510 volts just as it reaches the bottom of the wave. Once again I want you to think of C3 at this point as a 510 volt battery. As the input line voltage rollercoaster rides from the bottom troff, eg. negative peak of the sine wave, back to zero, C3 acting as a battery, now dumps its 510 volts into C4 charging it to 510 volts, but as the input line voltage rollercoaster ride continues up to the positive peak, as it rounds the top, C4 now has the additional positive peak value of the line voltage potential 170 volts, added to C3's 510 volts, charging C4 to a whopping 680 volts, and cycle after cycle keep biasing the diodes forward on the peaks of the waves, just enough keep C4 at 680 volts, even with loading applied.

    If it's negative voltage you want, swap the polarity of all the components, and presto, instant Negative Voltage Doubler, and ofcourse wiring two of them side by side one negative, and one positive, yields a plus, and minus powersupply, in which the combined voltage of both, can be obtained across the plus to minus DC terminals, for example if you made up two copies of these things, using my two stage example above, and the second copy was a negative Voltage Doubler the output from the minus DC to the plus DC would be one thousand three hundred sixty volts! Do you see why I call this site Zap Tek

    I have shown a two stage Voltage Doubler in this example, more stages, can be added if you want even more voltage, or you could just as well have stopped at one stage, if your needs would have been satisfied with only one stage. The trouble with doing this, using the above circuit, is the difficulty in finding suitably high enough voltage capacitors, after you get beyond two or three stages, a mere four stages and you're looking for capacitors with a working voltage of over a thousand volts, these are both rare, and needlessly expensive. The above circuit while simple to conceptualize, is far from optimal, I show below a slight modification of the hook up, that allows you to cascade dozens of these stages together, using only 200, and 400 volt capacitors.

    Something to bear in mind about ridiculously large arrays of Voltage Doublers, wired as above, to optimize for inexpensive, more easily obtainable capacitors. Unlike the previous easily comprehended non optimized version, in the optimized circuit circuit shown above each successive stage adds its current requirements to the previous ones load, so in a really large array of these circuits the one nearest the ground carries all the current of all of them above it, AND every new Voltage Doubler added to the end of the array, combines it's AC load with all of the others below it such that the impedance of C1, and therefore its capacitance must be high enough to effectively carry the combined current of all of them. Similarly, C2, C4, and all the rest of the even numbered caps in the entire array are all effectively wired in series, so their capacitance follows the rule of series capacitance, covered earlier in this course.

    I must admit to seeing large arrays of these in production. Two cases I know of where this was done, a Laser powersupply I've seen had about twenty stages of these things, cascaded together to form the five to six thousand volt excitation voltage for a low cost line powered HeNe Laser, and the technique was also employed to develop the second anode voltage of early, non-flyback design Oscilloscopes. If you do build a large array of these, be careful of placement of components, and insulators, a mere ten thousand volts will jump a gap of up to an inch under some conditions. If a spark does jump, shut off the power, and to avoid having to rewire everything, invest in some GC Electronics "Corona Dope" apply the stuff liberally around the area that is sparking, and allow it to completely dry before energizing the circuit, the volatile vapors, are flammable, and if a spark should jump in the presents of these vapors your circuit may catch fire.

    There is a standard for 90 Volts DC. Devices that use this voltage are inductive things like Relays, and Motors. As far as I can tell the power source these things were originally intended to operate with was halfwave rectified 120 Volts AC, with a back diode to retain current within the inductor during the other half cycle. If you operate most of these devices on 90 Volts DC, and measure their coil current, and then once again connected up as shown above on the left, the currents will be within a few percent of each other. As for the circuit on the right, it is only an example of a practical use of this concept. Of all of the experiments contained in this page, lesson 014, I expect you to try them all out if you possibly can, save one, the one above on the right hand side. It deals with an SCR, eg. Silicon Controlled Rectifier used as a 90 volt DC motor control device. It would be jumping the gun indeed to expect you to wire that one up, considering I've barely touched on transistors, as switches, and current gain devices, SCRs are complex devices comparatively speaking, and have as one of their inherent characteristics, a kind of Memory of their switched state. The only reason I placed the circuit here is to show a practical application of halfwave, rectification driving an inductive load, with a back diode to retain the coil current during the Off cycle. To elaborate just a little, the motor will switch on and run full speed with the voltage of a single flashlight battery applied to the input terminals of the circuit, and speed control of the motor can be achieved by driving the input with a carefully prepared, critically timed series of one volt pulses, directed to the same pair of input terminals.
    The last two experiments are what I consider novelties, in the circuit above use 1N4003 diodes, and although 60 volt lamps are optimum, in that a 60 volt lamp will light up full brilliance in this circuit, you can for the purposes of experimentation use standard 15 Watt 120 volt light bulbs, they just won't light as brightly. Incidentally the 1N4003 diodes will handle 1.0 Amp so the circuit will handle a 100 Watt bulb with ease. Ok after you wire it up, play with the switches, you'll find that the Red lamp, responds to the Red switch, and the Green lamp responds to the Green switch. They are completely independent of one another. Yet they do this over two wires, how is this possible? To find out, trace all circuit paths, for both half cycles of the incoming AC power.
    I have two 8" by 8" by 3" Glass blocks setting on my desk, it's an ordinary desk, I got when a warehouse was throwing out perfectly good usable stuff, this desk was one of the things they threw out. This desk is what I use for the bulk of my computing, although since I don't do bleeding edge, my computers are all over the house, forming a large LAN, large that is for a home. Most of them are refugees like the desk, low end Pentiums that I picked up for $10.00 typically. Across the top of the two glass blocks rests a pine plank, that serves as a shelf for the 14" SVGA monitor that I got for asking if I could have it, seeing as how it's fate would have been otherwise intertwined with a landfill somewhere. The under side of the pine plank, directly behind each of the glass blocks, are one for each, two 60 watt clear lightbulbs, the bulbs you see in the diagram above. Also mounted on the underside of the pine plank is a plastic project box with a long handled toggle switch protruding out the front, just beneath the monitor. That toggle switch is also the one in the diagram. What this circuit does is rather interesting, I will describe it viewing the bottom wire as the ground return, and the prong on the plug, that is connected to the fuse I will refer to as the input voltage, lamp 1 is the left lamp, and the other one is lamp 2.

    Ok here we go, first the switch open case. When the input is positive, no current flows, when it is negative, that half cycle the two lamps are wired in series across the 120 volts. Thus with the switch open, the bulbs are wired in series, and are powered up for only half the cycle. This results in only one quarter of the available power that would ordinarily light the lamp.
    Now the switch closed case. When the input is positive the left diode is reverse biased, the middle one is forward biased, and lights lamp 2. It also feeds current through lamp 1 via the right hand diode, thus lighting lamp 2, so for the positive half cycle, both lamps are wired in parallel. And during the negative half cycle they behave as they did in the switch open case. Thus with the switch closed, one half cycle is spent lighting them in parallel, and the other is spent lighting them as if they were wired in series. One half plus one quarter equals three quarter, so with the switch closed they light as if they are powered with 3/4 of their wattage. Throw the switch one way, open, and they serve as a night light, and throw the switch to the right they serve as ancillary lighting for the otherwise dark shadow that my pine plank would cast on the desk. If you looked at my internal link about Lamp Life formulas you would know what running a lamp at three quarters of it's rated power does to the life of the bulb, basically they never burn out, they just run and run, and run some more. The only time they ever do go bad, is when I do something like change the Glass Block, or move the shelf, then vibration, gets'em, the mechanical shock of moving things around is just more than a filament that's been given the softest life possible, for years on end can stand, and usually when I move the shelf I have to replace both lamps, due to mechanical shock.

    Summary
    I've given you about twenty low cost experiments, involving simple diode circuits, simple in that the demands of the diodes in these experiments are, for the most part, first approximation Rectifier Diode Applications that require only that the diode behave as a simple one way conductor of electricity. I've also given you a myriad of construction techniques along the way, with any luck you've improved, if they were absent, your soldering techniques, and hopefully took a gander at my tool abuse page for even more techniques. By now you should have some idea of what use an Oscilloscope is, and maybe are considering obtaining one, if it can be purchased inexpensively. Some people spend enormous sums of money, only to discover electronics is not their cup of tea, the Scope sits around the house for a few years, and then in a delirious moment of Spring Cleaning a Garage Sale happens, if you are there, you must understand that pressure from their Significant Other, often of a background that has no interest in electronics, sees such a valuable piece of gear as little more than an eye sore. Their loss, is your gain, this is your lucky day.

    Every one of these experiments demonstrates something interesting, and unless you already have electronics down cold, you need to wire them up, and try them out. I don't see how you can get this stuff by reading about it, the reason I say this is that the thing that teaches isn't the text of my web site, or a book, it's the seeming failures you encounter when you attempt the experiments. The failures you encounter require you to re-examine those comfortable, but incorrect assertions you've made while reading about the subject. The revisions you make to your thinking, in the endeavor to solve the puzzle that is causing the experiment to fail, are the revisions that actually teach you any discipline, and this is especially true of electronics.

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