To ensure the design is as open and accessible as possible, the circuit board design was created using KiCad, a free and open source PCB design package. 

Simplicity and ease of assembly were primary drivers for the design. The board can be fabricated as an affordable two layer board, and can even be hand-made as a single layer board using toner-transfer or other home-fabrication methods.

All of the original design files, schematics and the board fabrication outputs (Gerbers/Drill files) are freely available.

Schematics:

Amplifier Module Reference Schematics:

The load cell amplifier modules are a widely available commodity part. They appear to be a faithful implementation of the circuit suggested in the HX711 datasheet:

SAMD21 XIAO module schematic:

The microcontroller module is made by seeed studio and the full schematic for that part is available here: XIAO Schematic

Board Layout: