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The transmitter

So, without further ado, here is the schematic of the transmitter I built:

Yes, you've seen that right. All that's there is an AVR powered by a battery. The firmware does all the work. It overclocks the CPU to 24MHz, making the PLL run at 96MHz. It then starts a simple music player. Instead of routing the output of the player to a pin which is connected to a speaker, I feed it into a routine which varies the 96MHz PLL frequency by just a little bit, thereby frequency modulating the signal.

The music player, by the way, is a small routine I made ages ago. It takes a music file made by MONOTONE, a music program for composing PC Speaker tunes on an IBM PC-XT. Because the sound hardware it's made for is so simple, it was quite easy to make a player for the AVR for it.

For a whimsy schematic like that, a whimsy build should work:


You're looking at the programmed AVR, with the power supply wires lengthened a bit. They're connected to two button cells, which are connected together by a bit of duckttape. (And yes, the two buttons plus the AVR add up to three components... if you want just two components, use a single LiIon cell.)

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