Electrode Module 2

Purpose

This is an (untested) improvement upon Electrode Module 1 and implements the "Signal Processing Module" from circuit 5.1 and circuit 6. Essentially it calculates the difference between the voltages at the "in1" and "in2" pins, after applying a high-pass filter through C1/C2, and a pull-up/down through R1/R2 towards Vref to base the signal around the center.

Part placement

• C1: 100pF capacitor, 0805 package
• C2: 100pF capacitor, 0805 package
• C3: 100nF capacitor (exact capacitance not very important), 0805 package
• R1: 1MOhm resistor, 1% variance, 0805 package
• R2: 1MOhm resistor, 1% variance, 0805 package
• R3: 1kOhm resistor, 1% variance, 1206 package
• INA128: Texas Instruments INA128 instrumentational amplifier, SOIC/SO-8 package

Pins

The "out" pin goes directly to the Arduino ADC (or perhaps through a multiplexer)

The redundant Vref/GND/V+ pins can be used to wire multiple of these in a tree network topology, where only the first board needs to be directly connected to the power module.

Details

• Dimensions: 20 x 16mm

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• WARNING: NOT FULLY TESTED
• See blog post Wireless Prototype
• Source: PCB Layout file (for KiCad)
• Circuit: Circuit 5.1 (whole device)
• Date: 2021-05-12