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adafruit / Adafruit-MLX90614-Library

Arduino library for the MLX90614 sensors in the Adafruit shop
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Reading raw values is not possible #46

Open hacknus opened 8 months ago

hacknus commented 8 months ago

The raw values are stored in 16bit signed integers and can be read out. Please implement this in the library as well, currently only unsigned ints are implemented (temperature).

caternuson commented 8 months ago

Can you provide more information about what is needed here. Is this basically a request to make read16() public?

hacknus commented 8 months ago

read16 returns an unsigned 16 bit integer. However in the datasheet it says:

If the RAM is read, the data are divided by two, due to a sign bit in RAM (for example, TO1 - RAM address 0x07 will sweep between 0x27AD to 0x7FFF as the object temperature changes from - 70.01°C...+382.19°C). The MSB read from RAM is an error flag (active high) for the linearized temperatures (TO1, TO2 and Ta). The MSB for the raw data (e.g. IR sensor1 data) is a sign bit (sign and magnitude format)

This means we need to read the raw data and convert it to a sign and magnitude format (signed 16 bit integer). Also, I believe that the error flag for the temperature values is also not implemented.

caternuson commented 8 months ago

OK, still not sure what the request is then. The various read functions take care of all that converting.

hacknus commented 8 months ago

Doesn't the read16 just return the unsigned two's complement instead of the sign and magnitude format? return uint16_t(buffer[0]) | (uint16_t(buffer[1]) << 8); see here.

so we'd need a read16_signed method (private is okay, if there is would be a wrapper like for example readRaw1 and readRaw2).

And I also noticed that the CRC is never verified when reading data. So to put concrete requests: