January 30, 2013
about a year ago
I can understand the difficulty. I was able to make it work reliably by using a Manchester-type encoding (guaranteeing sufficient regularity of digital transitions in my serial signal) and adding a pattern to the front-end of each serial packet to give the receiver side software something to lock onto. Close to 100% now. However, I was surprised by the amount of effort required to go from a simple validation (for which I simply used a function generator) to a serial stream containing “intelligent” information. If someone were looking to use this for a very simple control signal, I might suggest a variable frequency output where different frequencies can be interpreted as different commands. That would be very fast and easy to implement with these parts.
I’ve got it working with 315MHz Tx/Rx on two separate modules that communicate with each other using the same frequency channel. It was harder than expected. Basically I wrote my own protocol and I turn off the receiver on a module when I transmit from it (power for receiver is from a digital output). If I did not do this it would take the receiver almost a full second to be able to lock onto a return packet. I’m not sure how this device works but it seems like if the adjacent transmitter on a module “yells in its own receiver’s ear”, then that receiver can’t lock onto the faint whisper from a distant transmitter on the same channel for about a second. It’s as if the device is somehow self-regulating to lock onto the strongest available signal level. Pretty cool as long as you know what is going on and can deal with it. Using the two separate frequencies would probably be easier. But I will end up with lots of nodes in my wireless system, so I was determined to make it work with a single frequency.
I’ve used both at 1KHz with no issues. An experiment transmitting from 200 feet away with a couple trees in the way and going around a corner into a window worked pretty well.
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