Custom decoder for Princeton remote

[Remi S]

Hi there! I've been a fan of this project for a long time, and I'm now trying to recognize a 4 buttons remote to trigger actions in my home automation stuff... The remote has no documentation but I tried to record the signal with my Flipper and it is decoded as a Princeton protocol: 

Filetype: Flipper SubGhz Key File
Version: 1
Frequency: 433920000
Preset: FuriHalSubGhzPresetOok650Async
Protocol: Princeton
Bit: 24
Key: 00 00 00 00 00 A1 41 98
TE: 340

In Flipper sourcecode I can see this (flipperzero-firmware/lib/subghz/protocols/princeton.c at dev · flipperdevices/flipperzero-firmware (github.com)): 

static const SubGhzBlockConst subghz_protocol_princeton_const = {
    .te_short = 390,
    .te_long = 1170,
    .te_delta = 300,
    .min_count_bit_for_found = 24,
};

So I tried running RTL_433 with the following arguments to see if it would register the remote: 

rtl_433 -R 0 -X "n=doorbell,m=OOK_PWM,s=390,l=1170,r=7000,bits=24"

It did not... Am I missing something?

[Christian Z.]

Sounds like the EV1527 protocol. There is an additional sync bit. You might need bits=25 or try bits>=24

[Remi S]

That helped me a lot! I was reading the Flipper Plotter wrong and I didn't see the 25th bit. I also had to increase the sample rate up to 1024k instead of the 250k by default, and now my remote is recognized. 

Thank you very much Christian!

[Christian Z.]

Glad to help. Also try

  -Y autolevel -Y magest -M level -M noise

to track levels, noise and most importantly estimated frequency. Your sender might be off the nominal 433.92, thus the need for a wider (1024k) band.