As someone suggested, a PIC with PWM would be a lot easier to use. Just
change the PR register. Someone else suggested an RC oscillator. I did
something similar to transmit 10kbps over 1.8MHz on IR. The IR also
carries FM audio at 2.3MHz and 2.8MHz. I'm using an LTC6907 oscillator.
The frequency is set by a resistor go ground. I lifted the bottom of that
resistor and added 100 ohms to ground. I drive the top of the 100 ohm
resistor with 3.3V logic through about 10k to give a deviation of +/-
100kHz (200kHz PP). On the receive side, I use an SA639, upconverting the
1.8MHz to 10.7MHz, running through a couple ceramic filters and a ceramic
quadrature detector. I use an LTC6202 as a photodiode preamp. I bias the
diodes through a tunable inductor that becomes resonant at 1.8MHz when
combined with the photodiode capacity.

Harold



-- 
FCC Rules Updated Daily at http://www.hallikainen.com - Advertising
opportunities available!
-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist