Before I start coding, I thought I would reality check a little. I have not used the “simple wireless” RLP modules yet – so I hope that some veteran users can add their 2 cents. Here’s my idea:
I need a transmitter / receiver that only communicates on and off messages. On the transmitter a force sensor will activate the transmission of an “on” message. The reciever will interpret this and then set a pin high to relay the on state.
My idea is to simply transmit b’01010101’ repeatedly on the “on” state, and nothing in an off state. The byte would serve as both the preamble and the data byte. As long as the receiver sees b’01010101’ it will hold the output pin high. If it sees nothing or noise, then it will ignore it and set the pin low again for the “off” state.
Does this make sense? In my view, this scenario avoids Manchester encoding and end bytes… etc, which are not needed for a simple switch. Is there anything I may be missing, and most importantly – will this scheme work with the “simple RF” RLP/TLP modules from sparkfun?
The transmitter will ALWAYS be transmitting (unless you power it down). It will just transmit all 0’s or all 1’s depending on how you hold that pin. I would transmit 10101010 instead of 01010101, but thats just my 2 cents.
Why 10101010 vs. 01010101 ? Please elaborate on the difference.
I understand that it will always be transmitting… My reciever will just be ignoring anything except the 01010101 to avoid noise (I’ll probably have it look for a few consecutive bytes). The transmitter will send 0s when the input from the sensor is low.
I’ve got the transmitter PIC all programmed on a 12f675 and it is sending 01010101 properly (1200bps bit-banged) when the sensor activates the comparator. So far so good. Now I just need to make the receiver PIC and wire in the TLP / RLP system. If I had the receiver simply look for 0x55 that would work, right?
I used 2 12F675s for the transmitter and the receiver. It is transmitting at 1200bps (bit banged). It simply sends ‘01010101’ when the sensors are activated (determined by the PIC transmitter).
The receiver simply looks for a start bit (0) and then fills an 8 bit register if a solid start bit is received. It makes sure that the signal is b’01010101’ and ignores everything else. It was very easy to plug into the RLP TLP.
I imagine the next steps – sending manchester encoded data would be easy. With a little patience, these units seem good.