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The load cells are from a bathroom scale which I tore down. Unfortunately they are only half bridges. Therefore I am using two of them paired as a full bridge combination.

Connecting the HX711 Board to the ESP

ESP  —- HX711

3.3V —- VCC

GPIO14 — SCK

GPIO12 — DT

GND —- GND

Software

I switched from LUA programming at NodeMCU to Arduino programming. It seems everything is more stable now. But the main reason was the Arduino library for the MPU6050 which I need for an other project.

Due to some issues with my cheap USB hub and the USB to TTL converter I need to program the ESP via my old laptop. But that is to slow for compiling Arduino ESP code. Therefore I am compiling the code on my desktop PC and copy the *.bin from /tmp/build* to the laptop via the sshfs. At the laptop I run

esptool.py -p /dev/ttyUSB0 write_flash -fm dio -fs 32m 0x00000 HX711Webserver.ino.bin

I don’t know whether the options are optimal or at least correct. But currently it works.

I am using the library-built-in averaging with 20 samples. As my HX711 breadboards came with rate pin hardwired to GND, I had to lift the RATE pin and wire it to VCC.

Calibration

Zeroing is easy. In my code the webserver on the ESP provides a link for zeroing.

It seems separate scaling calibration is needed for each bridge. Maybe it is even needed for each half bridge. But in the current setup with two half Bridges connected together, half bridge scaling can’t be done.

It is unclear whether temperature compensation is neccessary. I need to perform some temperature tests.

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