Whether you use RF or audio coupling to communicate, you will most likely be using an audio carrier to modulate the transmitter. A mark and space will be your "zero" or "one". Using Bell 212 tones will make it easier to troubleshoot because you can use a simple computer modem to test the modem circuits. You could either use a phone modem or design your own modulator/demodulator using EXAR, MOTOROLA, or Signetics chips, the latter probably more
trouble than its worth unless this is just a one-of-a-kind project.
Rick

Luc Bolly wrote:

> Hello all
>
> I'm a newcomer in this list. I'm discovering the PIC world (more specifically PIC 16Fxxx) since a few weeks. Until now, I've found all the answers either by my own experience or by looking in the Internet. But here, I'm blocked. So if someone can help ...
>
> Description
>
> I have two PICs (16F877 and 16F628) that must communicate. I use the integrated USART on both sides and everything works great if I cross-connect TX and RX lines between each PIC. In software, I use an interrupt (Timer 1 every 50 or 60 or ... ms) to send the data at my pace (2400 bps or 4800 bps). I use another interrupt on the other side (RCIE) and that's it. Not even implemented a buffer as each transfer is completed before next data is sent.
>
> The problem
>
> Once connected via a cable, it does work. But my goal is to replace the cable via a RF system. I'm not that good in electronic (mostly a system programmer), but I work with a friend who is supposed to be good. We are using transmitter and receiver from AUREL (we also tried another brand). The signaling is correct up to the transmitter, but after, we only saw "bzzz bzzzz bzzz" - nothing usable.
>
> The question
>
> Is there some special technics to be used with RF ? Does some of you have any idea about my problem ? Do I need to add some hardware excepted the transmitter and receiver (and the antenna of course) ?
>
> Thanks for any help.
>
> Luc Bolly
>
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