MCP9600 driver for CircuitPython

[cogliano]

FYI, here is my code for the MCP9600. You can test when the Adafruit boards are in stock, I have it working with another MCP9600 board. It currently does not support alerts, it only reads temperatures.

[caternuson]

Same here for using struct.unpack

[cogliano]

I simplified the return of _read_register() to return the entire array. Do you still think unpack is needed?

[siddacious]

I would suggest switching to using unpack. No need to re-invent the wheel, and it's a bit more succinct. Personally I trust it more than I trust my own ability to get the math right every time.

Your call, but I think it has its merits.

[cogliano]

So the code below uses the same algorithm as the Arduino MCP9600 driver, using CP and unpack. Is this any better? The results are the same.

[(https://github.com/adafruit/Adafruit_MCP9600/blob/master/Adafruit_MCP9600.cpp)]

        data = self._read_register(_REGISTER_DELTA_TEMP, 2)
        d = unpack(">xH",data)
        if d[0] & 0x80:
            # negative temperature
            value = d[0]*0.0625 - 4096
        else:
            # positive temperature
            value = d[0]*0.0625
        return value

[cogliano]

Also, does CP care about big-endian and little-endian integers or does it abstract it away? I had to use big-endian for the unpack on the PyPortal, don't know if other CP boards will be different. The original algorithm does not care.

[cogliano]

So thinking about this the return data will always be big-endian since the data is always big-endian when returned from read_register(). So the original question still stands, which algorithm is better?

[caternuson]

Using struct.unpack is better. It's not available in Arduino, so that driver does it manually.

Your _read_register puts the actual read results in buf[1] and buf[2]. So you should be able to do something like:

data = self._read_register(_REGISTER_HOT_JUNCTION, 2)
temperature = 0.0625 * struct.unpack(">h", data[1:])[0]

Note how you can indicate endian-ness to struct.unpack with < or >.

[ladyada]

sooo close! i will test this :)

[ladyada]

tested with hardware -> MCP9600 + itsybitsy! i think this is good to merge and we can add more later

[ladyada]

great work @cogliano
@kattni please get this into the bundle at your convenience - you can add your extensive code to it now that the sensor is working!