Reverse engineered: Flickering tea lights

Perhaps you have seen the flameless battery-operated candles, such as these tea lights.

You can buy this online for 99 cents. Oh, plus 9 cents tax and only $10.65 shipping. You can buy these in stores for the same 99 cent price, or down to almost 50 cents each in quantities of 20 or more.

Now that ours have finally died (120 hours total run time!) I was given permission to take one apart to see how it works. It was a lot simpler than I imagined. This device is simply a switch, battery holder, battery, and flickering LED soldered together (no wires; no other parts).

Most LED's (Light Emitting Diodes) require about 1.5 volts. They require a current-limiting resistor if the voltage is much more than the diode's forward voltage drop. But this device uses a 3 volt Lithium button battery with no external current-limiting resistor. That would burn out a typical LED. How does it survive? Where does the "flicker" come from? It turns out that this LED has tiny circuitry inside that limits current to the LED and creates the random flickering. It runs until the battery is completely depleted. I would guess it has a "joule thief" circuitry inside, too.

For more about this LED see the EvilMadScientist web site. This has quickly become a favorite site--they should make tee shirts!

Homemade Batteries: a "prove it" experiment

Usually these homemade battery experiments are designed for 6th Grade science class to teach basic chemistry and electricity principles. But you know what? I had never performed this experiment. I mean, I know you can make a battery* by sticking different metals in acid such as lemons or potatoes. I "know it" because I read it or heard it somewhere from someone who was supposed to know what they were talking about.

Hearsay. I believed it to be true, but I had never proved it to myself. Just like the sun is 93 million miles away. You knew that, too, did you? Prove it. I can't.

But I was able to prove that I can make a 0.9 volt chemical battery using a copper-plated penny and a zinc-plated galvanized nail stuck in an orange slice. I didn't get the 1.4 volts I expected from the carbon graphite from a carpenter's pencil to that same nail (only 1.08 volts, see below). And the penny to nickel cell didn't work at all in the orange (perhaps I really do need to use vinegar). The rusty iron screw was in the middle as expected. And I found out that a brass screw (made of roughly 65% copper and 35% zinc) acted electrically more like zinc than copper.

Carbon, copper, nickel, zinc, iron, and orange. DIY battery.

I also proved that I could hook up two of my 1 volt "orange batteries" together in series and get 2 volts. I had no doubt it would work from my studies of electricity. But now I've proven it to myself.

I think it is important, for everything in life, to always know why you believe what you believe. Don't take someone's word for it. Prove it to yourself.

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* - Technically, I created "cells" with metal electrodes and a catalyst. The term battery is more properly two or more cells linked together to give a higher voltage. Your car's 12 volt battery is 6 cells of 2.0 volts in series. Your flashlight "batteries" are 1.5 volt cells.

Electronics workstation on the cheap

My new living quarters happened to come with an overly large tool shed, complete with lights and electricity. It also came with a bit of junk, including a broken vacuum cleaner, a large plastic Christmas tree, and two old TV's.

What better time to set up an electronics work bench! Since my layoff in 2010 from Tektronix I haven't done anything with electronics. I've changed careers (a couple of times). But I've had this hankering lately--an itch, a yen, a desire--to get back into it a bit.

So last weekend I went to Fry's and bought about $120 worth of soldering and rework tools. If I can find an inexpensive scope someday, I'll have everything I need. But, until I start designing something complex, I can get by with only my DMM. As for electronics components, desoldering parts from those old TV's I "inherited" are going to be my first contributors to my parts bin--once I actually have a parts bin, that is. I guess a visit to Dollar Tree is in order.

My interests at the moment (now that computers have morphed into single-chip throw-away phones) include sensors, batteries, solar cells, and robotics. And the web is full of DIY projects for ideas, including a new favorite: Evil Mad Scientist Laboratories. You can't go wrong with a name like that!

My goal was to do this as cheaply as possible, yet get the best value I could. I pre-priced all the items ahead of time at Fry's and pretty much stuck to my list that originally had a total price of about $93, plus tax.

Tools

Velleman VTSS4N Solder Station	$22.99
MG Solder 0.5LB	$18.95
MG Solder Wick	$3.15
ECG Desoldering pump	$6.89
4-1/2 inch Tweezers	$3.99
Hakko Wire Cutter	$4.99
Jonard Wire Stripper	$7.99
Eclipse Glue Sticks	$4.99
Round Hole Breadboard	$8.69
NTE 5-Pair Alligator Clip set	$5.99
EZ-Hook Miniature Alligator Clips	$4.19
HBC Electrical Tape	$1.79

The extras I couldn't resist...

Heat Shrink Tubing Kit	$8.99
Extension cord, 3 outlets	$7.49
Vacuum Base Vise	$5.99
Cable Ties	$2.99

And, what I already have: DMM, Jewler's set of screwdrivers, needle nosed pliers, Philips screwdriver, slotted screwdriver, pliers, Xacto knife.

If I start working with integrated circuits I'll need an anti-static wrist strap. I could use a dispenser for rubbing alcohol and a brush to clean solder flux off components. But this basic set of tools is a good start. A "new" 2014 Rigol DS1052E 50MHz 2-Channel scope is $348 on Amazon, with 2 Hantek 100 MHz probes for $17. This is out of my budget right now, but I'll keep my eyes open for a deal on a used scope. If I start into radio, audio, digital, or computers I'll need a scope.