4 Three-Wire Load Cells Individually with ESP32

Projects General Guidance
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Hi everyone,

I’m building a food scale project with an ESP32, and I need to read 4 three-wire load cells (half-bridge strain gauges, 5kg) individually, not combined. My scale has electronics on some sides, making it uneven (heavier in certain areas). Using a single HX711 doesn’t work because it sums the load cell outputs, leading to inconsistent readings depending on where I place the object. For example, placing an item over the heavier side reads lower than expected due to the uneven baseline. Mechanically balancing the scale (e.g., adding weights underneath) is possible but cumbersome. Instead, I’d prefer to measure each load cell separately and apply calibration in software to adjust for the uneven weight.

My goal: Read each of the 4 load cells individually using only 4 wires to my ESP32: 3.3V, GND, SDA (I2C data), and SCL (I2C clock). Then, use software to tare out the uneven baseline (from the heavier electronics) and scale the readings to grams for accurate measurements.

Questions:

  1. Are there any premade modules that can read 4 three-wire load cells individually and interface with the ESP32 over I2C using just these 4 wires?
  2. If no premade module exists, is it feasible to design a custom PCB to do this? I’m a complete beginner in PCB design, so I’d need guidance on how to approach this (e.g., recommended components, tools, or resources).
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If you read the four three-wire cell individually, you’ll need eight completion resistors (so each cell forms a Wheatstone bridge). And you’ll need to find load cell amplifier(s) that uses I2C (the HX711 doesn’t, BTW). Or use four HX711 and the multi- library (which would use five pins total…four data pins and one clock pin).

Instead, I’d hook the four three-wire cells into the usual arrangement and try using trim pots (on one or more of the legs of the bridge) to balance it, together with one HX711.

ETA: you should use the Sparkfun HX711 with your ESP32. Apparently the only one on the market specifically tailored for use with 3.3v processors.

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