FM encoding of speech (also AM)

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It's Friday afternoon and as everything in the project I'm supposed to be working on is working perfectly, here's another bit of 'fun' code :-

It takes an audio input (speech quality only) and encodes it onto an FM carrier signal, so basically it's a voltage controlled oscillator (VCO). This signal is in turn PWM encoded (31KHz) by timer0 so that a simple RC filter on the output pin gives you a cheap 8 bit DAC. You will have to play about with carrier frequencies/filtering/anti-aliasing/signal levels etc to get a decent signal through it.

If you mask out the FM parts of the code and enable the AM bits, then it will AM modulate a carrier frequency, so the AVR is acting as an OSC with voltage controlled gain.

I'm using the ATtiny24V - it's a cheap way of getting a bit of signal processing. What's the use, erm, got me there ? It could be a way of transmitting a telephone quality audio link on an IR diode ? Or a demostration of the principle to a student ? The main thing it demostrates is that you shouldn't leave designers alone with a lab full of equipment ?

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<º))))><

I am only one lab accident away from becoming a super villain.

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What's the use, erm, got me there ?

The basis of a vocoder? "we will exterminate, we will exterminate"... etc. ;)

Cliff

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Now I like the way you're thinking :)

Maybe next time I manage to open up a bit of spare time, I'll make it do something 'Mr_Blue_Sky_tastic'.

By the way Kelly Groucutt died of a heart attack yesterday @ 63 :(

<º))))><

I am only one lab accident away from becoming a super villain.

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By the way Kelly Groucutt died of a heart attack yesterday @ 63

Good lord! I've always been a major fan of ELO. That's really sad.

(it's also a bit of an eyeopener when you are 46 and folks you considered "of your generation" start dying right left and center - gulp)

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For a vocoder you need bandpass filters, envelope detectors and controllable amplifiers. I did one in software on a PC about 9 years ago.