[Hackrf-dev] How to build a QT GUI fsk/nrz transmitter for a given device

[Dane Goodwin]

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
<http://www.grandviewscreen.com/pdf/manuals/Accessaries/1GD-868MnIII(RF_Remote_Controller).pdf>
.

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. The data is fsk/nrz
encoded.

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 block in this mail. The
Pattern Dump block comes from here <https://github.com/tkuester/gr-reveng>,
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!
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