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.

A load cell is a precision device particularly when it is paired with a sensitive high-resolution ADC such as the NAU7802. However, because of component variations and software accuracy limitations, the scale SHOULD NOT BE USED for safety, health, scientific, or commercial weight measurement applications.

Parts

Animated GIF showing CLUE board  displaying data from the many on-board sensors.
Do you feel like you just don't have a CLUE? Well, we can help with that - get a CLUE here at Adafruit by picking up this sensor-packed development board. We wanted to build some...
$44.95
In Stock
Angled shot of a Clear Acrylic Enclosure + Hardware Kit for Adafruit CLUE.
Here is a chic minimalist enclosure for your CLUE board! This case has been laser-cut specifically to accommodate the TFT display, tactile buttons, and...
$4.95
In Stock
Angled shot of a Strain Gauge Load Cell - 4 Wires - 1Kg.
A strain gauge is a type of electronic sensor used to measure force or strain (big surprise there). They are made of an insulating flexible backing with a metallic...
Out of Stock
Video of a pair of white hand's trying to bend a strain gauge. The gauge is connected to a breakout board which is also connected to an OLED display on a half-size breadboard. The numbers on the OLED display show high digit numbers.
If you are feeling the stress and strain of modern life a Wheatstone bridge and you want to quantify it, this handy breakout will do the job, no sweat! The Adafruit...
$5.95
In Stock
Angled shot of STEMMA QT / Qwiic JST SH 4-pin Cable.
This 4-wire cable is a little over 100mm / 4" long and fitted with JST-SH female 4-pin connectors on both ends. Compared with the chunkier JST-PH these are 1mm pitch instead of...
$0.95
In Stock
Front angled shot of 3 x AAA battery holder with on-off switch and 2-pin JST PH connector.
This battery holder connects 3 AAA batteries together in series for powering all kinds of projects. We spec'd these out because the box is slim, and 3 AAA's add up to about...
$1.95
In Stock
1 x USB cable
USB A to Micro-B - 3 foot long
1 x Clear Adhesive Squares
6 pack - UGlu Dashes
1 x Coupling Plate
3 Holes - 20x20 Aluminum Extrusion
1 x Cross-Plate
for 2020 Aluminum Extrusion
1 x Wire Ferrule Kit
800 pieces

This guide was first published on Aug 17, 2022. It was last updated on 2022-08-17 14:23:50 -0400.

This page (Overview) was last updated on Sep 29, 2022.

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