In my last post I talked about my self made scale. There are plenty of applications for a sensor that can sense the weight of things. But I guess the scale should not be tared (or set to zero) every time the ESP8266 wakes up from sleep. The load cell is basically a resistor that reacts to tearing and pushing of the metal bar. But like all resistors, they are prone to temperature drift. This means if I want to measure the weight of an object over a long time it either has to be under constant (room) temperature or I compensate for the drifting readings from the sensor by measuring the temperature and correcting the drift by software.

So for this test run I put the scale attached to the NodeMCU in a plastic box on my balcony. Together with the weight (drift) I’m also measuring the temperature. My hope is that this way I can learn how the load cell drifts with temperature. So now I hope for a cold night and a hot day to get a big range for my test;-)

Update (next day)

Scatter Plot of the load cell’s temperature drift: on the Y axis is the deviation from a tared cell, on the X axis the temperature

The uncompensated deviation from zero

The temperature at the same moment

The weight calculated after subtracting the temperature drift