Electrical – How to mount four 6-wire 10V load cells on Arduino or Raspberry Pi

amplifierarduinoload cellraspberry pi

I want to connect four 6-wire load cells (Tedea Huntleigh Compression & Tension Load Cell 300kg, 15V dc, IP67, product page and datasheet) into an Arduino or Raspberry Pi and get four independent readings. This is my first time dealing with load cells.

I would like to get an accuracy of 2kg and a range of 25-100 kg on each load cell. The load cells have a recommended excitation of 10V.

My understanding is that, to get a working prototype, I can:

  • not use the two sense wires in the load cell (first suggestion by DaveEvans in this Arduino thread)
  • use a breadboard, even though it's not meant for a sensitive circuit
  • use the 5V supply from the Arduino, which halves the output voltage from the load cell but does not require an extra power supply or an booster converter, with some decrease in precision of the reading
  • use an INA125P amplifier and the wiring in the first link of this thread and connect each load cell to a single analog pin in the Arduino Uno, which only has 5 analog pins
  • calibrate the reading from each load cell with two known weights and extrapolate linearly

Would this work? Which shortcuts would be the first to consider to improve the precision of the readings?

Best Answer

If you use a load cell rated for 200kg full load, with an output of 2 mV/V, and a supply voltage of 5V, then your output voltage will be 10mV for a 200kg load or 5mV for a 100kg load. A change in the load of 2kg will cause a voltage change of 0.1mV.

If you are digitizing this with a perfect ADC using a reference voltage of 5V you need at least 16 bits of resolution to see such a change in voltage. This will not happen with an Arduino. The ADC on an Arduino has 10 bits of resolution, so it can see changes of about 5mV. And we haven't even talked about accuracy yet.

So, you need to provide a differential gain of at least 100X if you want to use an Arduino. Otherwise, you need to find a better ADC. You also need to make sure that your analog reference voltage for the ADC, and the excitation voltage for the load cells, is as stable and accurate as you want your measurements to be.

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