Portable 3-in-1 Biosignal Monitor

Release status

The application, both supplied fonts, both STL meshes and the supplied MEGO Fusion archive are preserved unchanged. The builder confirms STEPico 3V3 and GND for modules other than EMG. The EMG connection record uses MEGO +VCC → +VS, -VEE → -VS, power GND → MEGO GND and signal GND → STEPico GND. The positive output is reported as +5 V; the negative setting has not been verified.

The source ZIP now includes six unchanged Python files: main.py, the latest device copy of SpO2Calculators.py, both fonts and the two-file max30102 package. The Pico reports MicroPython 1.20.0 on RP2040. The supplied Shell output confirms a successful st7789 import, and the builder reports prior hardware tests passed.

Educational build reference. Supply wiring does not establish compatible ADC signal levels or a verified body-connected measurement system. Conditioning and isolation require a separately checked setup.

Application and supplied libraries ZIP · STL ZIP · MEGO CAD archive · Release details and checksums

Module reference images

Product reference photos and details from the supplied CAD and EIM documentation screenshots. The original build photographs remain linked beside each reference image. The EMG illustration does not identify the amplifier IC in the actual build.

Image sources and provenance

Assembly outline

1. Open the two enclosure meshes and compare their board locations with the CAD layout. Verify model scale in the slicer; STL files do not declare units.
2. Record actual print material, orientation, settings, clearances and fasteners. These are not established by the supplied files.
3. Identify module connectors from the photographs. Plan access to USB-C, controls, the display and sensor connectors.
4. Trace the reported 3V3 / GND connections and the separate EMG supply path; check the analog conditioning and reference.
5. Use the source GPIO table for signal connections. GP2 selects the mode; GP3 resets the optical calculation buffers. Keep GP6 / GP9 for this SoftI2C source.
6. Record firmware and library versions, resolve the compatibility findings, then check display output, sensor detection, controls and all three modes on the device.

MEGO_Dual_v2.f3z is a module reference archive. Full assembly CAD, print settings and fastening details are still needed for a complete mechanical build guide.

STEPico setup · six steps

For a new board, follow all six steps. A board already running compatible MicroPython with st7789 can continue at step 5. These instructions adapt the manufacturer’s STEPico setup guide to the biosignal monitor’s display driver and source files.

1. 1

   Prepare Thonny and USB

   Install Thonny from thonny.org. Connect STEPico with a USB-C data cable.

2. 2

   Choose the firmware

   Use an RP2040 / Raspberry Pi Pico build that provides the st7789 display driver. The builder’s working board reports MicroPython 1.20.0; the exact original firmware image is unavailable. The driver project provides precompiled RP2 firmware as an upstream reference.

3. 3

   Enter BOOT mode

   Hold BOOT, press and release RUN, then release BOOT. Alternatively, hold BOOT while plugging in USB. A drive named RPI-RP2 should appear.

4. 4

   Transfer the UF2 image

   Drag the compatible .uf2 file onto RPI-RP2. STEPico restarts and the drive disappears. This installs the runtime; Python files are transferred through Thonny afterwards.

5. 5

   Connect the interpreter

   In Thonny, select the MicroPython Raspberry Pi Pico / RP2040 interpreter and the board’s serial port. Open the Shell. For a new installation, import st7789 to confirm that the display driver is available.

6. 6

   Copy and start the project

   Extract application-source.zip. In Thonny’s Files view, copy the four root Python files and the max30102 folder to the device root, preserving both files inside that folder. Open main.py and choose Run current script (F5).

A .uf2 file installs the board’s runtime. main.py and its libraries are copied into that runtime’s filesystem through Thonny. The st7789 project’s precompiled RP2 firmware is an upstream driver-inclusive reference; it has not been confirmed as the builder’s original image.

Directory structure

The two MAX30102 files belong inside the max30102 directory. The other four Python files belong in the device root. The supplied filenames containing upload suffixes have already been normalised in the source ZIP.

Supplied firmware references

UF2 block structure and internal version strings were inspected. These three uploaded files are references; they do not identify the current board’s reported 1.20.0 image. Their display-driver compatibility has not been established, and they are not bundled as project firmware.

Software and installation

The builder supplied this Pico Shell result on 21 Oct 2026:

(name='micropython', version=(1, 20, 0), _machine='Raspberry Pi Pico with RP2040', _mpy=4358)

This identifies the reported runtime version and platform. The builder also supplied <module 'st7789'> as the result of importing the display driver. The exact original firmware image has not been supplied.

Files in application-source.zip

Copy and check

1. Extract application-source.zip on the computer and preserve the max30102 directory.
2. Connect the Pico to Thonny and select its MicroPython interpreter. Open View → Files and preserve the existing device files before copying the release.
3. Copy the four root Python files and the max30102 directory into the Pico root. The directory contains __init__.py and circular_buffer.py.
4. On a fresh Pico, provide a compatible runtime with the st7789 driver available. The builder’s current Pico already imports it successfully; the source ZIP contains no firmware image.
5. The builder confirms prior successful tests of the display, controls and all three modes. This operational status is recorded from that confirmation.

Firmware image and operating record

A .uf2 file is a board firmware image used to install the runtime onto the Pico. It is separate from main.py and the Python library files. A display driver can be compiled into a firmware build. Supplied 1.25.0, 1.26.0 and 1.29.0 files are recorded as references above. A fresh-board installation needs a compatible st7789 driver runtime; those files do not establish the exact original 1.20.0 image.

The builder confirmed prior hardware tests passed on 21 Oct 2026; the original test date and detailed logs were not supplied.

Code review findings

Host checks pass for Python syntax, the calculator constructor and reset, empty / flat input and complete synthetic wave cycles. Every MAX30102 method called by main.py exists in the supplied driver. These checks do not run the code on the physical Pico.

A zero-baseline stress input still triggers ZeroDivisionError in the calculator. main.py also divides red_ratio by ir_ratio without excluding zero. The supplied buffer’s pop_head() has an issue outside the application’s current pop_red_from_storage() / pop_ir_from_storage() path. All files are preserved unchanged; these findings are documented for a later code revision.

The earlier candidate calculator lacked reset(); the latest device copy supersedes that candidate and includes the method. Its incomplete-cycle guard also supersedes the earlier missing-guard finding. The original firmware image and exact display driver version remain undocumented. The display import succeeds and prior hardware operation is confirmed by the builder.

Implemented modes and test record

0. ECG: GP28 waveform, threshold-crossing pulse estimate from the preceding ten seconds, with a two-second refresh after the first window.
1. EMG: GP27 reading compared with the GP26 potentiometer threshold. The displayed “voltage” divides read_u16() by 30000, so this prototype scale needs review.
2. Optical: MAX30102 red / infrared readings and a prototype oxygen-saturation estimate. The GP3 reset is not calibration against a reference instrument.

The supplied August 2025 conversation reports that replacing the STEPico restored operation and stopped observed heating. It does not establish the cause of the earlier fault. No servo or PWM output is implemented in the uploaded final program. Its sensor-missing startup message does not establish complete recovery behaviour. The builder reports prior successful hardware tests of the supplied program.

Manufacturer and software references

• STEPico board documentation
• MEGO Dual documentation
• EIM ECG tutorial
• EIM optical tutorial and display reference
• MicroPython RP2 ADC reference
• ST7789 firmware driver
• Thonny device file management