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SDR Help Wanted

SDR Capture

I have in front of me an Alevel 0214 ‘Smart LPG Tank Level Sensor’ from IMR – http://www.smartgasmetering.com/en/products/19-alevel-214 . Simply put, it converts the magnetic float level gauge on an LPG tank into bursts of 433Mhz data. It is designed, in turn, to work with an OKO 5100 receiver unit that then relays the data over the GSM network to your LPG provider. The OKO unit can support multiple gauges sending data to the reciever, so I suspect the gauge serial number will be embedded in the signal too. In this case, the serial number is 51355990.

Alevel 0214

I am trying to decode the data that is transmitted from the gauge. I’ve managed to collect (see below) a sample of readings from the gauge when it is in various positions. Helpfully, it blinks an LED with every transmission. I have been using https://github.com/jopohl/urh to capture and decode (sort of) the signals.

My issue is that whilst I can obtain hex from most of the signals, it does not stay the same amongst identical readings. I believe it to be ASK, with Non-Return-To-Zero encoding, and it will generally decode to 11 values. There’s a pre-amble of 3 A values, and a post-amble of what I think is 0.

For example 4 identical readings with the gauge at 0 results in aaa1140299c0, aaa91402ae0, aaaa2805270, aaa228052e0

Another 3 readings with the gauge at 11 percent results in aaa48a055d8, aaa2281530, aaa228120c0

Confusingly, the values change with every transmission. The unit itself is no larger than an egg timer, and has a listed battery life of 5 years. I doubt there’s a real time clock in there.

Each filename is prefixed with what the gauge says is the tank level. It’s not precise, but fairly close. There’s an additional v1-4 inserted into the filename, where the gauge reading has stayed the same, and another capture has taken place.

Can anyone help decode these signals?

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