Checksum on 12bit ADC value

[amaggs]

I am trying to decode a 4bit Checksum (or CRC code) that is being computed on a 12bit ADC value. The goal is to be able to intercept the ADC data and manipulate it (increasing or decreasing the value) before it gets delivered to another device. Below are samples of 12bit ADC values with the corresponding 4bit checksum/crc codes. There may be some +/-LSB errors in some of the samples.

I've tried a variety of ways to crack the checksum/crc algorithm but haven't been successful yet...

Following the 12Bit ADC value and preceding the Checksum/CRC are 3 nibbles that are constant in value: 0xE, 0xF, 0xF. I don't believe these values are used in the Checksum/CRC calculation but it's possible.

The order is: [12bit ADC Code][0xE][0xF][0xF][4bit Checksum/CRC]

0xC31,0x0
0xC29,0xC
0xC21,0xC
0xC19,0x8
0xC10,0x8
0xC09,0xE
0xC01,0xE
0xBFA,0xE
0xBF2,0xA
0xBEB,0x6
0xBE4,0x6
0xBDE,0x6
0xBD6,0x2
0xBD0,0x3
0xBCB,0x3
0xBC2,0x7
0xBBC,0x7
0xBB7,0xB
0xBB1,0xF
0xBAB,0x7

[santo_13]

Does the ADC manufacturer provide any documentation on verifying Checksum against the ADC data for integrity?

Can you share the details of the ADC?

[amaggs]

The ADC is embedded in a sensor and unfortunately all specifications and details of operation are intentionally obfuscated.

[santo_13]

So, you're hacking the sensor? Reverse engineering takes some effort, you can ask ChatGPT to decipher.

[amaggs]

Correct. It took me quite some effort to get this far already. I was hoping that the 4bit checksum/crc was perhaps some standardized algorithm that someone knew of. I can give ChatGPT a try. My worst case fallback is to try to create a lookup table for this value.