Pico Sensor Interface

NOTE: This code is WIP and in very early dev.

A Raspberry Pi Pico-based sensor interface project that provides real-time monitoring and data transmission using Modbus RTU communication protocol. This project is built using PlatformIO and the Arduino framework.

Features

• Real-time sensor data acquisition using 12-bit ADC
• Pulse rate measurement with interrupt-based detection
• Modbus RTU slave communication (115200 baud)
• Dual-core utilization for efficient task handling
• Motor power control functionality
• Thread-safe sensor data handling using FreeRTOS mutexes

Hardware Requirements

• Raspberry Pi Pico
• 4 - 20mA Sensors (100R shunt resistor)
• Active low RPM sensor (1 pulse per revolution)
• Current monitoring over I2C
• USB Serial Modbus RTU communication

Software Dependencies

• PlatformIO
• Arduino framework for RP2040 (Earle Philhower core)
• ModbusRTUSlave library

Getting Started

1. Install PlatformIO IDE (VS Code extension) or PlatformIO Core
2. Clone this repository:

   git clone https://github.com/ScionResearch/pico-sensor-interface.git

3. Open the project in PlatformIO
4. Build and upload to your Raspberry Pi Pico

Project Structure

• /src - Main source files
  • main.cpp - Primary application logic
  • sys_init.h - System initialization and configuration
• /lib - Project libraries
  • ModbusRTUSlave - Modbus RTU communication library
• /include - Header files
• /test - Test files

Configuration

The project can be configured through the platformio.ini file. Current settings:

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

Communication Protocol

The device operates as a Modbus RTU slave with the following specifications:

• Slave ID: 1
• Baud Rate: 115200
• Data Format: RTU
• Holding Registers: 10 registers available for control and monitoring

Modbus Register Map

The following table describes the Modbus holding registers used in this device:

Register Address	Name	Data Type	Description
40001 (0x0000)	CH0_MA	FLOAT32	Channel 0 current measurement in mA
40003 (0x0002)	CH1_MA	FLOAT32	Channel 1 current measurement in mA
40005 (0x0004)	CH2_MA	FLOAT32	Channel 2 current measurement in mA
40007 (0x0006)	PULSE_RATE	FLOAT32	Measured pulse rate in Hz
40009 (0x0008)	MOTOR_MA	FLOAT32	Motor current measurement in mA

Notes:

• All FLOAT32 values use two consecutive registers (32 bits)
• Register addresses follow the standard Modbus convention where 4xxxx indicates holding registers
• The device uses standard IEEE 754 floating-point format
• Values are updated every ADC_INTERVAL for current measurements and in real-time for pulse rate

Contributing

Feel free to submit issues, fork the repository, and create pull requests for any improvements.

License

Not licensed

Author

Jeremy Peake - Scion Research