I know that there are several ways to do this, but I need the cheapest. The range must be at leats 20 ft. All I really need is four 1 or 0 outputs, really just something i can feed into a pic.
I might need different frequencies because, because the application might be such that all transmitters would be sending at the same time. Part of the application is to detemine which of the signals came in first. Basically all I need is 1-bit of information from each transmitter.
There are some dedicated encoder/decoder chips for this kind of thing, one of which might do what you’re asking. Holtek makes some. (They’re the kind of thing that’s used in car keyless-entry transmitters.)
How important is it that the system reliably determine which button was pressed first if they’re almost simultaneous? If you’re using one frequency, then you’ll have some sort of (maybe very simple) collision resolution algorithm, but it might not let the first transmitter through first. But you could get around that by having each transmitted packet contain a timestamp indicating how many milliseconds that transmitter’s button has been held down. That’ll require more smarts on the transmit/receive ends, but that might be easier than having multiple frequencies.
The system completely depends on which transmitter is activated first. It doesn’t matter how long the transmitter is being pressed. Just which one shows the rising edge first. There is a very real possibility that they could be activated at the same exact time or very close.
What about a few of the Simple RF Link - Transmitter - Receiver - SKU Number:RF-KLP. At just $12 per pair, I can get a few pairs on different frequencies. If there was an even cheaper and more simple version, I could just use that. Due the fact that all I am sending is 1-bit, it can be super simple. I will just have to set up a signal detecting circuit on the receiver side. Does anyone know of a cheaper solution?
http://www.handhelds.ws/need_circuit.jpg.