You are now the proud owner of a box of "overflow" from my design workbench. There is a bunch of stuff here, and I'll describe some things you can do with it. You'll learn a bit of electronics, and hopefully have some fun.

Everybody starts electronics by taking apart something that somebody else built. In the old days it was toasters and motors and radios and war surplus stuff. You learned about resistors, voltage, and power by noticing that low value resistors connected to high voltages got hot and burned up! Transistors were similar, but they didn't usually smoke- they just mysteriously stopped working. Yes, I wrecked a lot more things than I fixed- at least for a while.

The best way to learn electronics is to experiment. Hook up some circuits and see what they do. I'm going to give you some hints, but I'm not going to tell you everything...

Project #1 – A Voltmeter

It's hard to do much without some way to measure voltage. Sure, the light lights, the motor runs, or the resistor gets hot. But you don't really know much about something unless you measure it. (I'm paraphrasing Lord Kelvin, a.k.a. William Thompson. He's dead, but you might want to look him up in the encyclopedia anyway. See if you can find the exact quote. Bet it isn't easy. While you're at it, look up Alessandro Volta, 1745-1827- it's his volts you're using.)

You should find a couple meters in the box. These are sensitive- if you connect them to a voltage, they will most likely burn out. A commercial voltmeter uses a switch to insert various resistors in series with a meter to make it more or less sensitive. A large value resistor allows the meter to measure high voltages, a small value resistor allows the meter to measure low voltages.

Here is a schematic of a simple 0-10V meter circuit you can build. Later, you can improve it with more resistors and a switch to give more ranges. Right now it will just be a simple zero to ten volt meter. All the parts should be in the box. (somewhere...)

[need schematic showing resistor value for the sensitivity of the specific meter]

Try the meter on various batteries and see if you get the voltage marked on the battery.

Do you know ohms law? It's easy, and it lets you calculate what resistors you need for various things. It looks like this:

Voltage=Current X Resistance





Voltage is also known as electromotive force, or emf for short. Because of that, voltage is often represented in formulas as "E" for emf. Nobody wanted to use "C" for current, as it was already in use for other things, so "I" was adopted. At least "R" is still resistance. So remember:

"E" for voltage

"I" for current

"R" for resistance

Now we have E=IR, R=E/I, and I=E/R. A bit of practice. You have a ten volts across a twenty ohm resistor. You have volts, you have ohms, you need what? Ah! Current. OK, I=E/R. So I must equal ten volts over twenty ohms: I=10/20, so I=1/2 Ampere (or amps, for short).

Hints: You can always start with "ground" as zero volts. Add up series resistors until you can calculate the current through them. If you don't seem to have enough information, make some assumptions. Say something like "Let's just say I have one volt here. Now what sort of current will flow?"

Project #2 – LEDs (Light Emitting Diodes)

After you get done with this project, you will probably have some DEDs (Dark Emitting Diodes)! There are also SMDs (smoke emitting diodes), and FEDs (flame emitting diodes), but try to avoid those- they smell. Anyway, LEDs are not like light bulbs. They only light in one direction- they have polarity. Like meters, if you hook them directly to a voltage source, they will light only once. Very briefly. You have to limit the current through them with a resistor. Most LEDs like to run at about 0.02 amperes, a.k.a. 20 milliamperes, or 20 mA. You can calculate the best resistor using ohms law. Let's say you have a nine volt battery. OK, E=9. We already know that I=0.02, so R=E/I, or 9/.02. R=450 ohms. Whoa, not so fast. Wire this circuit up and measure the voltage across the resistor. Now measure the voltage across the LED. Calculate the current through the resistor. Hmm. What didn't we take into account? What should the resistor value really be?

Project #3 – Capacitors- Buckets of Electrons

This is an easy one, but important. Find a big capacitor, maybe about 1000 microfarads. It should be marked 1000 uF. (Yes, now you've got to look up another dead guy. This time it's Michael Faraday, 1791-1867. Get it, Faraday.) The capacitor has polarity just like the LED. Notice the stripe with the minus signs down the side. Hook the minus lead of the capacitor ("the cap") to the minus lead of a 9V battery. Hook the plus lead of the cap to the plus lead of the battery. Count to three. Now disconnect the leads. Carefully touch the tips of the leads together. Waddidja get? Do it again, but this time touch the leads to your LED and resistor circuit from above. What did it do and how long did it do it? Try it with the voltmeter and resistor.

1000 microfarads is considered a pretty big capacitor. It's .001 farads. Radios commonly use tiny capacitors, like 100 picofarads or smaller. Pico means "move the decimal twelve places", so 100 pF equals .0000000001 farads!

Project #4 – A Galvanometer

This is a classic experiment. Make a coil of wire about six inches in diameter. The more turns of wire, the merrier, but twenty will probably work. Now find a compass. Not the kind with a pencil, but the kind you use when you're lost. (OK, if you had a compass, how did you get lost in the first place?) Support the compass in the center of the coil of wire, maybe with a block of wood. Now apply a small voltage to the coil of wire. Say, a 1 1/2 volt D cell through a few hundred ohms of resistance. Can you deflect the needle? What arrangement of needle and coil gives the most sensitivity. Can you measure the sensitivity and " calibrate" the device? (hint- answer should be in amperes per degree or something similar) Is this more or less sensitive than the voltmeter you built? Yes, you have to look up another dead guy. He's an Italian, Galvani. Why don't frogs like this guy? While you're at it, try looking up galvanometer. It may be harder to find.

Project #5 – Learning About Radio– Your First Resonant Circuit

Yeah, I know nobody listens to AM, but if you figure out how to do this, you can probably do one for FM. Hey, I said I wouldn't tell you everything! We're going to build a resonant circuit that "assists" an AM radio pick up stations. It has the effect of making the antenna larger, and helps select the desired station out of the crowd. A resonant circuit is nothing more than a capacitor and an inductor (a coil) wired together. We want a resonant circuit that resonates at the same frequency as the radio station we want to receive. There's a nice adjustable capacitor in the box. Each section is about 530 picofarads, or 1600 picofarads when all wired together. Set half-way, that would be 800 picofarads. The middle of the AM band (550-1600) is 1075. The formula is usually shown as:


But, we need to know L, not F. F is frequency, L is inductance, C is capacitance, and Π is 3.14159265. I'll rearrange the formula like this:


For the middle of the AM band, and for a typical adjustable capacitor of 800 pF we get:

formula   henries

Cool. Now, how many turns of wire will make a coil of 27.4 microhenries? Well , there's a formula for that, too:


N is the number of turns, L is the inductance in microhenries, a is the radius in inches, and b is the length of the coil (not much in our case- use an inch). So we get:

formula   turns

So here's the project. Make a wood frame about 20 inches on a side (roughly 12 inches radius, but square). Use something lightweight, or you could just tape the wire to a large sheet of cardboard. Wind 12 turns of wire on the frame, or coil it on the cardboard. Connect the capacitor to the coil (in parallel). Now, put the whole thing near your radio, tuned to the station you want to listen to. Tune the variable capacitor. Can you find a position where the station gets louder? Can you tune in stations that you couldn't before? If the middle of the band isn't near the middle of the capacitor range, add or subtract turns of wire from the coil until it is.

If the AM band is 550 to 1600 Khz, and the FM band is 88 to 108 Mhz, what would you have to do to adapt the device for FM? Try it!

Project #6– Perpetual Motion?

You should find two motors in the box. Try running them with a 9V battery. Not too long, or the battery will run down! Now, spin one of the motors with your fingers. Remember how easy it is to turn. Short the two wires together. Now spin it again. Hmm. Now connect an LED to the two leads and spin it. OK, now the voltmeter.

It would appear you have a method to convert mechanical motion to electricity. You also seem to have a way to convert electricity to mechanical motion. How can you connect these things to build a perpetual motion machine? Does it work? If so, great! File for a patent and get rich. If it doesn't work, why not? What is the flaw in any perpetual motion scheme? Think about this until you understand and believe it completely. Also, think about it in a cosmic sense- is the motion of the solar system a perpetual motion machine? Is energy being lost, causing it to "run down"? If you can find a supply of energy to run your "machine" (like a solar cell) does that count? Is it cheating?

That's enough for this installment. Let me know how you do, and if you'd like more things to try. I'll leave the rest of the parts in the box to your imagination. Get some books. Read 'em!

P.S. I did the formulas in a hurry. They might be wrong! If you have trouble, look up the formulas and check 'em. Also, you should look up a bunch more dead guys! Try James Prescott Joule (1818-1889), James Watt (1736-1819), George Simon Ohm (1789-1854), Andre Marie Ampere (1775-1836), Charles A. Coulomb, Joseph Henry, and James Clark Maxwell (1831-1879).

One more interesting thing. I've given you the dates for quite a few famous men that lived in the 1700s and 1800s. Figure out how long they lived, then look up the average life span for that time period. Look it up for right now. Was playing with electricity good or bad for them. Or did it matter at all?