FM transmitter + encoder/decoder?

[bd13]

i want to be able to control some relays from some distance away, i have gotten some schematics on FM audio transmitters that transmit the distance i need, want i would like to know is if i could attach the encoder and decoder ICs here (HT-640,HT-648L) to the audio input and output on the tx/rx and have it work (control relays). i looked at the digrams of theoretical use of the ICs and i think you could just use the audio in on the transmitter as the data out on the ICs, please tell me if i'm wrong or crazy. thanks

 

[mechie]

Not that simple !

The encoder outputs a digital data stream at 1/33rd of its oscillator frequency.
If you wish to transmit this as 'audio' then it needs further processing to make it look like audio.

-There are no guarantees on this- but I reckon ...
If you set the osc frequency to something like 1kHz/8*33 (about 4.1kHz)
and arrange the digital output to enable a 1kHz oscillator whenever there is a logic '1';
As the transmitter generates an output bit of 1/33rd of its osc frequency the audio osc will generate about 8 cycles of audio (with me so far ?), this can be transmitted as audio.

The reciever will produce a series of 1kHz 'bursts', the shortest of which will be about 8 cycles, 8ms long. A detector can now resolve this back to a digital signal by simply detecting sound/no sound.

I chose 1kHz as it is easily in the audio band, 8 cycles should give a timing resolution that the decoder can deal with.

 

[bd13]

ummmm.....ok, i really don't follow you on that, well i do sort of, but in how to build that i'm lost. how much trouble would it be for you to draw a schematic of that? it would be appreciated. thanks.