AVR-Chat

On 18 Aug 2005 at 21:05, Thomas Keller wrote:

>    You can obtain single chip filters that could be easily ruend using
> external R-C values to your two frequencies, then use Schmidt Trigger on
> the output of thefilter to generate a trigger pulse everytime the signal
> is at that frequency.  Just run those to a pair of interrupt enabled
> inputs on your AVR, and count the pulses.  Since you know what the bit
> timing is, it should be fairly easy to distinguish noise, and to
> identify mutliple bits of the same freqency.


	The two filter approach can be done in software by the AVR.  
	Take a look at this document:

	http://www.baycom.org/~tom/ham/da95/d_dspmod.pdf

	I designed a radio modem for a client using exactly that modem.
	The C routines need to be translated to assembly for speed and 
the math can be done in 16-bit fixed point.
	After demodulation the remaining task is straightforward.

	Mark