Hey all
I'm new to SDR stuff, and am trying to learn as much as I can. As hands-on practice is best, I found a cheap and simple rf device to practice with. Specifically,
this remote.
It transmits an (almost) static signal, which can be replayed using hackrf_transfer. Each button repeats the same signal, but with a counter which increments as long as you hold the button down. Each button transmits 12 bytes which include a preamble, sync word, command, said weird counter, and a null byte to signal the end of the transmission. As I understand, the data is fsk/nrz encoded, but I've included a screenshot of the waveform I see right after the Quadrature Demod block, so you can see what I see. From the doc, the baud rate is 2400.
I'd like to create a software version of the remote, which transmits the same signals as the remote, but using GRC to encode the message properly. This is where I'm stuck, so, I'm asking for help with two things:
1. How do you go about creating a qt gui source block which outputs something that GRC can use? What datatype should this block output?
2. How would I encode that output in such a way that it would be identical to what the remote transmits? I tried using the GFSK modulator with various settings, but that didn't work, and I'm not sure why.
Regarding what I've done so far: I created a receiver for the remote in GRC. I used two custom blocks, so I've only attached a screenshot of the graph in this mail. The Pattern Dump block comes from here, and basically looks for a given preamble, and passes the bits that follow to another block as a message. I wrote the receiver block, which checks those messages, and runs a different os command depending on what button was pressed.
Thanks in advance for the help!
grandview_message.png
grandview_rx.png