Consistently brewing that crowning cup of coffee involves attention to the precise addition of ingredients and control of the brew ratio, tempered with practiced technique. Perhaps it's time to apply a little more science to the art.
The Clue Coffee Scale can accurately measure the weight of the ground beans or the extraction output, getting closer to an exact and repeatable approach for creating your preferred brew. To measure the contents of a container, the scale can be zeroed with a push of a button to subtract the container's tare weight.
The scale uses a load cell sensor device that consists of a very sensitive resistance array (a strain gauge) attached to a metal bending beam. When connected to an exciter voltage, the resistance array provides a differential voltage output signal proportional to the torque of the mass placed on the load cell. The signal voltage is very low so a sensitive amplifier and high-resolution analog to digital converter (ADC) are used to provide a microcontroller-compatible measurement.
The Adafruit NAU7802 24-Bit ADC - STEMMA QT board has everything needed to connect a load cell and provide measurements for the Clue. Add a CircuitPython program, and the Clue Coffee Scale is born.
John Park built a version of the coffee scale for use with his primo espresso station. Check out the Build the Coffee Scale section of this guide for the step-by-step approach he used for his custom scale. A trenta-sized thank you goes to John for creating a practical and beautiful working scale.
This guide will show how to build, calibrate, and code the scale. Your perfect cup of Java awaits.