mlx.getFrame(frame) returns "math domain error"

[AutomatedAI]

Hello,

I am trying to run the basic example to stream data over i2c through the MCP2221. The Serial number is pulled from the MLC90640 easily but each time mlx.getFrame(frame) is called I get a "math domain error" if I print the exception. Any ideas as to why this may be happening? I am using Ubuntu 16.04 and python 3. Thanks!

[caternuson]

By basic example, do you mean the mlx90640_simpletest.py one in this library? Can you post the full text of the error code you get when you try running it.

$ export BLINKA_MCP2221=1
$ python3 mlx90640_simpletest.py

[AutomatedAI]

Apologies and and happy to clarify!

I have my export BLINKA_MCP2221=1 set correctly and the error is in regard to the python3 mlx90640_simpletest.py

Everything seemed to be working correctly when running the program. I get the "MLX addr detected on I2C" and the serial number of the device.

When the following lines of code are run (I added the "as e" and "print e" to figure out what is happening in the library )
try:
mlx.getFrame(frame)
except ValueError as e:
# these happen, no biggie - retry
print(e)
continue

I print the ValueError each iteration as "math domain error" so I would guess a cos value or something is incorrectly being calculated.

Thanks for your help!

[AutomatedAI]

After debugging a bit, the error occurs in the second iteration of "self._CalculateTo(mlx90640Frame, emissivity, tr, framebuf)". I was able to replicate on a raspberry pi so it is probably related to some math feature of python in Linux. I'll see if I can figure out a solution. Fingers crossed!

[BLIII]

I also am encountering this exact same error and started debugging the same way that @AutomatedAI did (with printing the exception). When I did this, I received the following:

MLX addr detected on I2C ['0x102a', '0xbfb7', '0x6187']
math domain error
math domain error
...

When I set BLINKA_MCP2221=1 I receive the following:

Traceback (most recent call last):
  File "mlx90640_simpletest.py", line 2, in <module>
    import board
  File "/home/pi/thermal_imager/.env/lib/python3.7/site-packages/board.py", line 33, in <module>
    from adafruit_blinka.agnostic import board_id, detector
  File "/home/pi/thermal_imager/.env/lib/python3.7/site-packages/adafruit_blinka/agnostic/__init__.py", line 18, in <module>
    chip_id = detector.chip.id
  File "/home/pi/thermal_imager/.env/lib/python3.7/site-packages/adafruit_platformdetect/chip.py", line 87, in id
    "BLINKA_MCP2221 environment variable "
RuntimeError: BLINKA_MCP2221 environment variable set, but no MCP2221 device found

I am not sure if it matters but I am attaching the MLX90640 to the RPi using Qwiic connectors and a Sparkfun pHat. I will continue to debug tomorrow to see if I get anywhere.

[BLIII]

After some more digging, I believe this is related to this PR: #18

If I make the following dirty hack to the _CalculateTo function in adafruit_mlx90640.py, the code will at least run:

                Sx = (
                    alphaCompensated
                    * alphaCompensated
                    * alphaCompensated
                    * (irData + alphaCompensated * taTr)
                )

                if Sx < 0:
                  continue

                Sx = math.sqrt(math.sqrt(Sx)) * self.ksTo[1]

My board has two broken pixels that causes Sx to be negative so the code chokes when calculating the sqrt.

Is there a way to get the PR mentioned above merged and released?

[jepler]

A third user on discord help-with-circuitpython has reported the same problem.

[ladyada]

@jepler if they apply #18 does that help?

[ladyada]

going to close with the assumption #18 fixed it. if not, we can re-open!