Hi, I apologize if this is not the appropriate place for this question. I have tried searching this forum and the sparkfun site / internet more broadly but I have not been able to find a solution. I am trying to build a set of scales using the 5kg TAL 220B load cells hooked up to the NAU7802 amplifier board. Each amplifier board is then connected to a raspberry pi using the TCA9548A multiplexer to connect all of my amplifier boards to a single raspberry pi via the QWIIC HAT for raspberry pi. I am using this code I wrote to operate the scales https://github.com/pardojer23/pi_Qwiic_scales. My code relies on the PYNAU7802 library https://github.com/BrunoB81HK/PyNAU7802. I am able to connect to my scales just fine however, when I try to calibrate them I am unable to get a stable calibration. After calibrating with a known weight the scale will be off by 100 grams to several Kgs and the readings are also not repeatable. I’m using a 500 gram calibration weight to calibrate the scales. Any suggestions about what might be wrong with the load cells I am using? I have encountered this problem on a half dozen TAL220B load cells so I suspect the issue is with the setup and not the load cell itself. See the attached picture of my setup.
Couple things:
Your setup creates a lever arm so depending on where you place the weight, that will change what the sensor is seeing and your final weight. Moving your weight just an inch is going to change the output.
All that plumbing connected to your bins is going to affect your readings. See if you can get the water(?) that’s moving into the bins to fall from the pipe into the bins rather than have the pipe connected to the bin. Water flowing through the pipes will affect your readings.
YellowDog:
Couple things:Your setup creates a lever arm so depending on where you place the weight, that will change what the sensor is seeing and your final weight. Moving your weight just an inch is going to change the output.
All that plumbing connected to your bins is going to affect your readings. See if you can get the water(?) that’s moving into the bins to fall from the pipe into the bins rather than have the pipe connected to the bin. Water flowing through the pipes will affect your readings.
Thank you for these suggestions. I’ve been testing the system without the pots or irrigation so the issues I’m having are not as a result of the irrigation pipes. The lever arm suggestion makes sense to me however, I’m having issues even when no weight is applied. Ie. I calibrate the scale and then remove all weight and the scales don’t read 0. Additionally, I had the scales working with a very similar setup for awhile and it didn’t seem to matter if the weight was shifted around in the pot holder. Do you have any other thoughts about what might be preventing me from getting a good calibration or suggestions for a better setup of the load sensor?
Try a setup like the picture below where the weight is concentrated in the area directly above the load cell.
Were you able to resolve this issue?
I’m having exactly the same problem, and it appears to me that the drivers for the nau7802 do not work on my raspberry pi 4.