The Clue Coffee Scale is a CircuitPython project designed to measure the weight of ground coffee beans or the espresso machine's extraction output to achieve repeatable results for your preferred brew. The scale uses a load cell sensor that consists of a very sensitive resistance array (a strain gauge) attached to a metal bending beam. A specialized NAU7802 Analog-to-Digital Converter (ADC) breakout board connects to the load cell and measures the slight changes in the array's differential voltage, calculating the weight of the mass placed on the load cell.

The Clue interfaces with the NAU7802 ADC board and automatically updates a colorful graphics display showing the results in both ounces and grams. 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.

Hardware components:

• CLUE - nRF52840 Express with Bluetooth LE, Adafruit PID: 4500
• Clear Acrylic Enclosure + Hardware Kit for Adafruit CLUE, Adafruit PID: 4675
• Strain Gauge Load Cell - 4 Wires - 1Kg, Adafruit PID: 4540 (or equivalent)
• NAU7802 24-Bit ADC - STEMMA QT / Qwiic, Adafruit PID: 4538
• STEMMA QT / Qwiic JST SH 4-pin Cable - 100mm Long, Adafruit PID: 4210
• 3 x AAA Battery Holder with On/Off Switch and 2-Pin JST, Adafruit PID: 727
• USB cable - USB A to Micro-B - 3 foot long, Adafruit PID: 592 (or equivalent)
• Clear Adhesive Squares - 6 pack - UGlu Dashes, Adafruit PID: 4813
• Aluminum Extrusion Corner Brace Support (for 20x20), Adafruit PID: 1155
• Coupling Plate - 3 Holes - 20x20 Aluminum Extrusion, Adafruit PID: 1216
• Cross-Plate for 2020 Aluminum Extrusion, Adafruit PID: 1220
• Wire Ferrule Kit - 800 pieces, Adafruit PID: 5131

Software dependencies:

• Adafruit CircuitPython

... the font file:

• helvB24.bdf (placed into the project's fonts folder):

The font file can be found in the fonts folder in the project bundle of the Clue_Coffee_Scale repository.

... the following CircuitPython Libraries (placed into the project's lib folder):

• adafruit_apds9960
• adafruit_bitmap_font
• adafruit_bmp280
• adafruit_clue
• adafruit_display_shapes
• adafruit_display_text
• adafruit_lis3mdl
• adafruit_lsm6ds
• adafruit_register
• adafruit_sht31d
• cedargrove_nau7802
• neopixel
• simpleio

CircuitPython libraries can be found in the latest Adafruit CircuitPython Library distribution or installed individually using circup.