Firmware for an Arduino-based 3-channel geophone digitizer that communicates with a Raspberry Pi over RS-422.
Part of the rpi-seism ecosystem — reads analog signals from a GD-4.5 geophone via an ADS1256 ADC, formats samples into binary packets, and streams them to the Pi over a heartbeat-controlled full-duplex RS-422 link.

• 3-channel differential sampling — reads EHZ, EHN, EHE via ADS1256
• Runtime-configurable ADC settings — sampling rate, PGA, and data rate sent by the Pi at startup; no recompilation needed
• Settings handshake — blocks until a valid SettingsPacket is received, echoes it back for end-to-end verification
• Heartbeat-based streaming — starts sending data only after receiving a heartbeat byte; stops after 1 second without one
• Jitter-free timing — uses lastSampleTime += interval to prevent drift accumulation
• XOR-checksummed 16-byte packet format
• No direction-control pin — RS-422 is full-duplex; TX and RX are separate pairs, the driver is always enabled
• Automatic platform detection — SPI pins and ADS1256 constructor selected at compile time via #if defined blocks
• Multi-platform — AVR, RP2040, STM32, ESP32, Teensy

The ADS1256 constructor and SPI pins are selected automatically at compile time based on the target platform. The active defaults per platform are:

To use an alternate SPI bus, pass the appropriate macro via build_flags in platformio.ini (see Installation).

The ADS1256 requires a stable 2.5 V reference. Most modules include a REF5025; if yours does not, provide an external 2.5 V reference.

RS-422 is full-duplex — TX and RX use separate twisted pairs. No direction-control GPIO is needed; the firmware writes directly to Serial with the driver permanently enabled.

git clone https://github.com/rpi-seism/reader
cd reader

Upload to your board:

pio run -e nanoatmega328new --target upload   # Arduino Nano
pio run -e rpipico          --target upload   # Raspberry Pi Pico
pio run -e esp32dev         --target upload   # ESP32
pio run -e blackpill_f411ce --target upload   # STM32 Black Pill
pio run -e teensy40         --target upload   # Teensy 4.0

To use an alternate SPI bus, add build_flags to the environment:

[env:rpipico]
...
build_flags = -D USE_SPI1   # RP2040: use SPI1 instead of SPI0

[env:esp32dev]
...
build_flags = -D USE_HSPI   # ESP32: use HSPI instead of VSPI

[env:blackpill_f411ce]
...
build_flags = -D USE_SPI2   # STM32: use SPI2 instead of SPI1

Monitor serial output after upload:

pio device monitor -e nanoatmega328new

RP2040 — the official raspberrypi platform does not support SPI.setSCK() / setTX() / setRX(). The Earle Philhower core via the maxgerhardt platform is required:

[env:rpipico]
platform          = https://github.com/maxgerhardt/platform-raspberrypi.git
board             = rpipico
framework         = arduino
board_build.core  = earlephilhower

ESP32 — the generic esp32dev board does not define LED_BUILTIN. The firmware falls back to GPIO 2, which is correct for most ESP32 WROOM modules. Override via build_flags = -D LED_BUILTIN=<pin> if your board differs.

1. Install the ADS1256 library via Sketch → Include Library → Add .ZIP Library
2. Open src/main.cpp
3. Select your board and port, then upload — the correct constructor and SPI pins are selected automatically

On boot the firmware calls getSettings() which blocks until a valid SettingsPacket is received from the Pi.

Out-of-range values are clamped (ADCGain to 6, ADCDataRate to 11). The packet is echoed verbatim — the Pi verifies the echo before starting its heartbeat loop.

Fixed 16-byte ADC_Packet frame sent at the configured output rate:

• STOP — LED blinks at 1 Hz, ADC halted, waiting for heartbeat
• STREAMING — ADC sampled at configured rate, packets sent over RS-422

Any byte received from the Pi resets the 1000 ms heartbeat timeout. Missing the timeout returns to STOP.

Each cycle calls cycleDifferential() four times — the fourth call is discarded but required to advance the ADS1256 multiplexer back to the first channel pair. Removing it causes channels to rotate incorrectly.

Stuck in getSettings() — the Pi must send the SettingsPacket first. Verify RS-422 wiring (TX+/TX− and RX+/RX− must not be swapped) and that the daemon's Reader thread is running.

No data after handshake — verify the Pi is sending heartbeats every 500 ms. Both sides must be at 250 000 baud.

LED not blinking — device is stuck waiting for the settings handshake (solid off). If blinking at 1 Hz, handshake succeeded but heartbeats are not arriving.

Noisy ADC readings — verify the 2.5 V reference is stable. Check shielding and grounding on geophone cables.

Channels rotating — the fourth cycleDifferential() (discard) call has been removed. Restore it.

RP2040 compilation errors (setSCK/setTX/setRX not found) — the official raspberrypi platform is being used. Switch to the maxgerhardt platform with board_build.core = earlephilhower (see Platform notes).

ESP32 LED_BUILTIN not declared — add build_flags = -D LED_BUILTIN=2 to the esp32dev environment in platformio.ini.

GNU General Public License v3.0