troubleshooting new colorimeter

  • About two weeks ago, I purchased and assembled the colorimeter. It was working beautifully -- up until today.

    This afternoon, I started taking readings of ammonia using the API ammonia test kit. It looked like it calibrated fine, but the readings all came back 0.00. I rebooted my computer (Colorimeter software v.4 and v.5 tried on MacOS Catalina on a 2012 Mac Mini), but that didn't help.

    Next step, I loaded the software onto a MacBook Air - same problem: after calibration, all readings are zero.

    Just FYI, the samples definitely had plenty of color (the A620 values on a spectrophotometer were all above 0.78). Any suggestions on what to try?

  • @pablosoup1

    You might try testing to see if the there is an issue with either the LED or the sensor board.

    First test the LED. Open up slider on top of the colorimeter and ensure that the sensor is exposed to light - ambient room light should be fine. Make sure there is light hitting the sensor. With the top open and light hitting the sensor start the colorimeter-basic program and try running the "Calibrate" routine. You should see the LED flash red, green, blue ,white in sequence. Note, you can increase the duration which each LED color is on by increasing the number of samples - say from 500 to 5000. If the LEDs are flashing all four colors in sequence then they are working.

    Next check to see if the sensor board is working. Again to do this again you will want to expose the colorimeter sensor to ambient light. In this case it might be easier to unscrew the top of the colorimeter and pull out the sensor board. It should be connected to the Arduino by the gray ribbon cable. It doesn't need to connected to the LED by the 4-connector cable for this test. Expose the sensor to room light and run "Calibrate" in the colorimete-basic program. Then partially obstruct the light hitting the sensor with your hand or a piece of paper and run the "Measure" routine. As less light is hitting the sensor you should see nonzero absorbance values for all color channels.

  • Thank you for the suggestions. i'd tested the LEDs (they work), but not the sensor board. I'll give that a go this morning and report back.

    Even with this (relatively minor) glitch, I think highly enough of the colorimeter that I've already bought a second for off-site use in water quality monitoring.

    Now, if someone would help me figure out how to put the LEDs and sensors at a right angle to each other, rather than a direct pass-through, I could have a fluorometer for measuring chlorophyll A and phycocyanin!

  • Will,

    I followed your instructions on checking the sensor board - and everything is fine now. I'm not sure if it had an impact, but I did switch to a new USB hub that may provide a bit more power than the ancient Mac Mini I was using before. I know that the USB connection can definitely cause issues with Arduinos - but I do not know that it was the cause of this problem.


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