Hi,

I've been trying to decode the signals from an RF temperature and
humidity sensor. The sensor is a small battery powered sensor which
comes as part of an home 'weather station'
The messages are all 36 bits long, I've worked out most of it, but it
looks like there may be a 4 bit checksum or crc at the end, which I
have been unable to work out.

Here are some examples, with the information I know. Each message
contains a ID (which changes every time the sensor is reset and it
used to 'pair' the sensor to the display unit),  channel id, 12 bit
signed temperature reading and humidity as 2 BCD digits. I think the
last 4 bits are some sort of checksum/crc

This is what I know of the protocol so far

ID?=A0 CH ?????? Temperature =A0Humidity =A0CRC?
0001 01 001010 010100110000 1100 0010 1100
0001 10 001010 111100110000 0010 0010 0111
0001 11 001010 011100110000 1100 0010 0111
0001 10 001000 111000110000 0010 0010 0101
0001 10 001000 000100110000 0010 0010 1001
0001 10 001000 100100110000 0010 0010 0001

I think the bits marked ?????? include battery level, and I'm not sure
what else.

I have lots of data, so I'm thinking that it should be possible to
work out the CRC algorithm, however I've tried various crc calculators
such as http://www.lammertbies.nl/comm/info/crc-calculation.html but
have not been able to find the crc parameters.

I've also tried crcbfs.pl to find the crc parameters, however this
method requires that I have at least 2 strings of different lengths
(which I don't have).

Does anyone have any suggestions of how I might work out this CRC (if
indeed it is a CRC)?

Regards

Matt

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