Protocol Bytes with dynamic element

[Mamut1975]

Congrats to the nice project. Very cool HW. I tried to analyse the protcol for door open at my BJ room station using my scope and an UART decoder. I could read all bytes.
2x 13 bytes are visible. I wonder because in byte 9 is a dynamic section. Byte 13 seems a CRC byte with unknown calc approach.

Every time when I open the door a different random number show up.

Any idea what this is? Any idea how the CRC is calculated?

I got for example the following 13 bytes

55.FF.03.0D.40.01.10.01.B1.51.9F.05.1F
55.FF.03.0D.40.01.10.01.45.51.9F.05.CC
55.FF.03.0D.40.01.10.01.2F.51.9F.05.AC

[Mat931]

Hi!
I wrote some code for calculating the checksum and encoding / decoding the protocol that is now part of the ESPHome project. The checksum function can be found here. Byte 9 seems to be just a randomly generated number.

[Mamut1975]

Thank you for the link. This was the missing part👍