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FoxilloScope (STM32G474 Oscilloscope)

An accessible, wireless oscilloscope built around low-cost development hardware: the ST Nucleo-G474RE board and an M5Stamp C3U (ESP32-C3) module.

  • Bipolar signal measurement
  • Dual-channel
  • Up to 8 MHz sampling rate
  • 12-bit resolution
  • The user interface runs in a web browser on desktop and mobile devices
  • Communication via Wi-Fi or Bluetooth Low Energy (BLE). Bluetooth requires a compatible browser (e.g., Google Chrome).
  • No installable application required

The goal of this project is to turn inexpensive, readily available development components into a practical, portable oscilloscope with live-streaming over Wi-Fi or Bluetooth LE — requiring minimal soldering and no custom PCBs.

💡 Developer Note: For firmware compilation, hardware debug configurations, jumper setups, and local debug servers, see the Developer & Contributor Guide.

Key Features & Hardware Design

  • Affordable Hardware: Total hardware cost is under €25 / $30 (minimal soldering, no custom PCBs needed)
    • Analog front-end (AFE) built on the ST Nucleo-G474RE board – handling signal capture and triggering
    • M5Stamp C3U handles wireless connectivity and hosts the web server
    • Signal conditioning built with six Schottky diodes (BAS40-04 dual-diodes or equivalent) and five resistors
    • Inexpensive oscilloscope probes (not included in BOM)
  • Bipolar Signal Measurement: On-chip analog front-end (AFE) supports true bipolar AC/DC signal measurements (both positive and negative voltages) around virtual ground.

    ⚠️ Important Grounding Notice: Users must not connect probe ground clips to the board's GND pins. Always connect probe ground clips to the board's dedicated Virtual Ground output. This provides a clean mid-rail reference for bipolar measurements and prevents shorting power rails.

  • Input Voltage Range: Measurable range −1.65 V to +1.65 V (1:10 attenuating oscilloscope probes recommended); safe input range −30 V to +30 V.
  • Input Signal Protection: A resistor and diode protection network protects MCU inputs against out-of-range signal spikes.
  • Multi-Transport Web UI: Single-page web dashboard accessible via Wi-Fi (WebSockets), Bluetooth LE (WebBluetooth), or USB (WebSerial).

Assemble at Home (Quick Start)

  1. Flash the Nucleo Board & Set Production Jumpers:
    1. Connect the Nucleo board to your computer via USB. A virtual USB drive will appear.
    2. Copy the FoxilloScope-Production.bin firmware file from the latest release assets directly onto the Nucleo's USB drive.
    3. Wait a couple of seconds and then disconnect the board.
    4. Configure Jumpers (blocks onboard ST-LINK in off/reset state):
      • JP1: Closed
      • JP5 & JP3: Open
  2. Flash the M5Stamp C3U:
    1. Connect the M5Stamp C3U or another ESP32-C3 board to your computer via USB.
    2. Use the Foxilloscope ESP32 Web Flasher to upload ESP32 part of the oscilloscope
  3. Solder Protection & Connections:
    1. Prepare the signal conditioning components:
      • Schottky Diodes: 6× Schottky diodes (BAS40-04 dual-diode sets were used, but almost any Schottky diodes with reverse voltage $V_R \ge 40\text{ V}$ and minimal junction capacitance fit).
      • Resistors: $2\times 1\text{ M}\Omega$ resistors and $3\times 3\dots 6\text{ k}\Omega$ resistors.
    2. Solder the input protection network and interconnections as shown in the wiring diagram below: Wiring Diagram
    3. Attach measurement probes to Channel A / Channel B inputs, and connect probe ground clips to the Virtual Ground output.
  4. Verify Operation:
    1. (Optional) If the debug STM32 firmware is flashed, connect test signal outputs A/B to the Channel A/B inputs or probes:
      • Test Signal A: Small-amplitude decaying sine wave
      • Test Signal B: Triangle wave (−1.65 V to 0 V)
    2. Bluetooth LE (BLE) Connection:
      1. Power up the system and navigate to http://f-scope.local/ in your Chrome browser.
      2. Click the Bluetooth button at the bottom-left to connect, then select the F-SCOPE-xxxx device.
      3. Test if oscilloscope is working correctly.
    3. Wi-Fi Connection:
      1. Connect to the FoxilloScope-xxxx Wi-Fi network.
      2. Open http://f-scope.local/ or http://192.168.4.1/ in your browser.
      3. Test if oscilloscope is working correctly.
  5. Wi-Fi Setup:
    1. Connect to the FoxilloScope-xxxx Wi-Fi network.
    2. Open http://f-scope.local/wifi or http://192.168.4.1/wifi in your browser.
    3. Set up Wi-Fi credentials (Until ESP32-C6 gateway is used, only 2.4 GHz Wi-Fi is supported).
    4. Reconnect back to your Wi-Fi.
    5. Open http://f-scope.local/ in your browser.
  6. Printable Device Label(optional):
    1. Open Sticker Generator in your web browser.
    2. Enter the 4-digit hex MAC ID (xxxx) of your device.
    3. Print the label to attach to your board or enclosure.

(where xxxx represents the device ID – the last four hex digits of the ESP32 MAC address)

M5Stamp C3U Setup & Status Indications

The M5Stamp C3U acts as the wireless bridge connecting the STM32 to your browser.

Pin Connections

  • GPIO 6: UART TX (connects to STM32 UART RX)
  • GPIO 7: UART RX (connects to STM32 UART TX)
  • GPIO 2: Data line for onboard SK6812 RGB LED (WS2812 protocol)

Onboard RGB LED Statuses

LED Color Status / Meaning
Green Client actively connected over WebSocket
Blue Client actively connected over Bluetooth LE (BLE)
Orange Wi-Fi station connection failed (fallback Access Point is active)
White Connected to Wi-Fi network, waiting for web client
Purple Idle in Access Point mode (FoxilloScope AP), waiting for connection
Blinking Pink STM32 firmware update complete (power cycle required)

Deployment & Web Access

1. Wireless Gateway Mode (Default)

Connect your computer, phone, or tablet to the ESP32 gateway (either directly via its FoxilloScope AP or through your local Wi-Fi network) and open:

http://f-scope.local/

The ESP32 serves the web frontend and streams data in real time via WebSockets.

2. Standalone CDN / GitHub Pages Mode

The web app can also be hosted on any static HTTPS server (e.g. GitHub Pages). In this mode, the browser connects directly to the hardware via:

  • WebBluetooth: Connect wirelessly over BLE.
  • WebSerial: Connect directly over USB at 460,800 baud.

Documentation & References