I built a simple magnetic inductance coil using:
For transmitter:
28 awg magnet wire in a "pancake coil" (flat spiral) npn transistor (TIP31C)
2 resistors in parallel
battery (tried a 3 volt battery, 2 3-volts hooked together, and 9-V. 9-V got too hot too quickly)
For receiver:
28 awg magnet wire in tight coil LED
My question:
How can I stop my LED from burning out each time I get it too close to the 9-V battery?
The whole point of this project is to allow someone to basically "play" with the receiver coil and make the LED go to a maximum or minimum brightness at their leisure. If I use the 9-V battery, I get the distance I want, but heat build-up is terrible and the LED burns out if it gets too close to the transmitter.
So I guess a second question:
How do I keep the LED from burning out AND how do I keep my 4 inch minimum receiver distance (for decent light from LED, about half the possible brightness from about 3-4 inches away) and stop my transmitter from getting too hot? (I plan on the transmitter/receiver running for at least a few hours and be reuseable)
P.S. The receiver needs to be as simple as possible, (2 or 3 small parts maximum if possible). And the transmitter can be no larger than the back of the average person's hand. (I was thinking "stacking" the pancake coils together and using 2 6-V power sources to make the magnetic fields addative, but that would increase the weight of the transmitter and I'd like to keep that to a minimum).
If knowing what it is for would be helpful then:
I plan on putting the transmitter in the back of a leather glove, growing borax or alum crystals over the tranceiver, and making the crystals "glow" via magnetic induction for a few wizard/witch costumes for halloween (hence the weird size/weight restrictions). Also I'm worried about people who may try to "play" with the gloves (with their hands not being in the gloves) and put the crystal with the LED too close to the transmitter, thus burning out the LED (and this would be a major issue as the LED is currently inside a crystal and cannot be replaced).
Anyway, thoughts/suggestions for my 2 problems would be helpful. Thank you.
Schematics that I found online, only difference is that I used the magnet wire for the transmitter pancake coil as well as the receiver.