ESP32 WiFi Kitchen Scale

Over the years I've seen a few posts on Reddit demonstrating the use of a load cell with an internet-connected microcontroller as a weight-based filament sensor for 3D printing. I decided to embark upon a similar project, retrofitting a $10 kitchen scale.

See full writeup and project guide here.

What do we need for the retrofit?

Hardware modules

• ESP32 or similar microcontroller with WiFi connectivity - for our purposes we'll be writing the code in C++ with the Arduino IDE.
• HX711 load cell amplifier - this module is going to allow us to get a stable, accurate reading from the load cell.
• SSD1306 i2c OLED screen (128x32)

Libraries

• HX711 by bogde
• Adafruit_SSD1306 by Adafruit
• ezButton by ArduinoGetStarted
• We'll assume that you have the EEPROM, WiFi, and WebServer libraries as they are part of the ESP32 core.

Smart scale schematic

Calibration

• Press the left (UNIT) and right (TARE) buttons at the same time to enter calibration mode
• Place an item of a known weight onto the scale
• Use the left(-)/right(+) buttons to set the calibration value. Double pressing a button will move the number by 10.
• When the correct value in grams is displayed, press the two buttons at the same time once again to set the calibration value.
• Remove the item from the scale and press tare to zero out the scale, if necessary.