Teardown
Know your sensors
HealthyPi Move runs six distinct sensor ICs across two boards, fronted by two MAX32664 algorithm hubs that convert raw signals into vital-sign outputs. This page walks the signal chain — what each part does, where it sits, and what it gives you.
Signal-chain diagram
The four optical/biopotential front-ends do the analog acquisition. The two MAX32664 hubs each run Analog Devices’ clinical-grade PPG algorithms locally — so the nRF5340 just receives finished vital-sign values rather than having to process raw waveforms in firmware.
Optical PPG — wrist and finger paths
Move has two PPG paths that can’t run simultaneously. They share the same downstream processing pipeline, so a given measurement uses one or the other.
Wrist PPG (MAX86141 + MAX32664-C)
The MAX86141 is the always-on path — it sits between the four gold ECG electrodes on the underside of the watch, with two photodiodes and four LEDs. Its 3 LED drivers can address up to 6 LEDs through an external mux, and 2 readout channels operate concurrently. This is what drives continuous heart rate.
The MAX32664 Version C algorithm hub processes the MAX86141 stream for wrist-based heart rate and SpO₂.
Finger PPG (MAX30101 + MAX32664-D)
The MAX30101 is a more compact integrated PPG module (LEDs + photodetectors + low-noise AFE + ambient-light rejection on one die). For Move, it lives in an external cable accessory that plugs into the USB-C port — pull the cable out of the box, plug it into the side of the watch, and clip the finger sensor on.
The MAX32664 Version D algorithm hub processes the MAX30101 stream for finger-based heart rate, SpO₂, and blood-pressure trends. The fingertip site gives a much cleaner pulse than the wrist, which is why blood-pressure trending uses this path.
ECG and bio-impedance (MAX30001)
The MAX30001 is a single-channel biopotential AFE plus a single bio-impedance channel — the same chip we ship as a breakout board for makers.
In Move it does two jobs:
- 3-lead ECG. Two leads come off the gold-plated pads on the underside of the watch. The third lead is the stainless-steel bezel on top, contacted via pogo pins arranged 180° apart under the cover. Two-handed measurements (your other hand’s fingers on the bezel) form the closed loop needed for high-quality traces — see the ECG screen page for usage.
- Respiration via bioZ — measured by the same chip when configured for thoracic impedance sensing. Not surfaced as a vital sign in the current firmware, but the front-end is there for custom builds.
Body temperature (MAX30205)
The MAX30205 is a clinical-accuracy temperature IC (±0.1 °C over the physiological range) — also available as a QWIIC-compatible breakout for makers.
In Move, the IC sits below the bottom housing and reaches the skin via the small round silver thermal contact just above the lower gold electrode pad. The internal sigma-delta ADC produces 16-bit digital readings.
Motion (BMI323)
The BMI323 is a 6-axis IMU — accelerometer + gyroscope on a single die, with on-chip motion-triggered interrupt logic. In Move it does:
- Step counting for the Activity screen
- Wake gestures for the screen-on logic
- Motion gating for ECG (so the recording is rejected if you move during the 30-second window)
Source files
Full schematics and PCB layouts for all the above are in the hardware repo: