• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

FM transmitter + encoder/decoder?

Status
Not open for further replies.

bd13

New Member
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

New Member
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

New Member
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.
 
Status
Not open for further replies.

Latest threads

EE World Online Articles

Loading
Top