ESP32 NextPM Sensor Reader

An educational ESP32 project for reading particulate matter (PM) concentrations from a NextPM sensor via UART serial communication. This simplified implementation is designed to help students understand serial communication protocols, binary data parsing, and sensor integration.

📋 Table of Contents

• About Particulate Matter
• Features
• Hardware Requirements
• Wiring Connections
• Software Requirements
• Installation
• Usage
• Understanding the Code
• Expected Output
• Troubleshooting
• Learning Objectives
• License

About Particulate Matter

Particulate Matter (PM) refers to tiny particles suspended in the air that can be harmful to human health. This project measures three types:

• PM1.0: Particles with diameter < 1.0 micrometers
• PM2.5: Particles with diameter < 2.5 micrometers (common air quality metric)
• PM10: Particles with diameter < 10 micrometers

Values are reported in µg/m³ (micrograms per cubic meter).

Features

• ✅ Reads PM1.0, PM2.5, and PM10 concentrations from NextPM sensor
• ✅ Uses UART serial communication with 8E1 parity
• ✅ Binary protocol with checksum validation
• ✅ Non-blocking timing pattern with millis()
• ✅ Extensively commented code for educational purposes
• ✅ Real-time data output to Serial Monitor
• ✅ Error handling and debugging support

Hardware Requirements

Component	Specification
Microcontroller	ESP32 development board
Sensor	NextPM (NPM) particulate matter sensor
Connections	UART (Serial) communication
Power Supply	USB (for ESP32) + sensor power supply

Wiring Connections

Connect the NextPM sensor to your ESP32 as follows:

NextPM Sensor	ESP32 Board
TX (Transmit)	GPIO 39 (RX)
RX (Receive)	GPIO 32 (TX)
GND	GND
VCC	External power supply (check sensor voltage requirements)

Important Notes:

• The NextPM sensor typically requires an external power supply (check your sensor's datasheet)
• ESP32 GPIO 39 is input-only (perfect for RX)
• Do not connect sensor VCC to ESP32 3.3V unless your sensor specifically supports it

Connection Diagram

┌──────────────┐              ┌──────────────┐
│              │              │              │
│   NextPM     │              │    ESP32     │
│   Sensor     │              │              │
│              │              │              │
│         TX ──┼──────────────┼─→ GPIO 39    │
│              │              │   (RX)       │
│         RX ←─┼──────────────┼── GPIO 32    │
│              │              │   (TX)       │
│              │              │              │
│        GND ──┼──────────────┼── GND        │
│              │              │              │
│        VCC ──┼─→ External   │              │
│              │   Power      │              │
└──────────────┘              └──────────────┘

Software Requirements

• PlatformIO - Modern embedded development platform

  • Recommended: Use PlatformIO IDE extension for VS Code
  • Alternative: PlatformIO Core CLI

• VS Code (optional but recommended)

  • Download from: https://code.visualstudio.com/

Installation

Step 1: Install PlatformIO

Option A: VS Code Extension (Recommended)

1. Open VS Code
2. Go to Extensions (Ctrl+Shift+X)
3. Search for "PlatformIO IDE"
4. Click Install

Option B: Command Line

pip install platformio

Step 2: Clone the Repository

git clone http://gitea.aircarto.fr/PaulVua/esp32_NPM_only.git
cd esp32_NPM_only

Step 3: Open in PlatformIO

Using VS Code:

1. Open the project folder in VS Code
2. PlatformIO will automatically detect the project

Using CLI:

pio project init

Usage

Building the Project

pio run

Uploading to ESP32

1. Connect your ESP32 to your computer via USB
2. Upload the code:

pio run --target upload

Monitoring Serial Output

View real-time sensor readings:

pio device monitor

Or combine upload and monitor:

pio run --target upload && pio device monitor

Exit the monitor: Press Ctrl+C

Cleaning Build Files

pio run --target clean

Understanding the Code

The code is organized into clear sections with extensive comments:

Main Components

1. Hardware Configuration (main.cpp:18-30)

   • Serial port definitions
   • GPIO pin assignments

2. Helper Functions (main.cpp:50-107)

   • checksum_valid(): Validates sensor messages
   • send_concentration_command(): Sends read request to sensor
   • print_data(): Debug output for troubleshooting

3. Sensor Reading Function (main.cpp:109-242)

   • read_concentration(): 11-step process documented in detail
   • Protocol parsing and data extraction
   • Error handling with timeout protection

4. Arduino Functions

   • setup(): One-time initialization (main.cpp:244-286)
   • loop(): Non-blocking repeated execution (main.cpp:288-318)

Key Concepts Demonstrated

• Binary Serial Protocol: Reading structured binary data
• Checksum Validation: Ensuring data integrity
• Non-blocking Timing: Using millis() instead of delay()
• UART Communication: 8E1 parity configuration
• Error Handling: Timeout protection and validation checks
• Data Scaling: Converting sensor's fixed-point integers to floats

Expected Output

After uploading and opening the Serial Monitor, you should see:

=== NextPM Sensor Reader ===
Simplified version - Concentration readings only
Averaging: 60 seconds, Update: every 10 seconds

Waiting 15 seconds for sensor initialization...
Sensor ready. Starting measurements...

--- Reading NextPM Concentrations ---

=== Particulate Matter Concentrations ===
PM1.0:  12.3 µg/m³
PM2.5:  18.7 µg/m³
PM10:   24.5 µg/m³
======================================

Readings update every 10 seconds.

Troubleshooting

No sensor response

Symptom: ERROR: No response from sensor

Solutions:

1. Check wiring connections (TX/RX crossed correctly?)
2. Verify sensor has power
3. Wait for full 15-second initialization period
4. Check sensor is compatible with 115200 baud, 8E1 parity

Invalid checksum errors

Symptom: ERROR: Invalid checksum

Solutions:

1. Check for electrical noise on signal wires
2. Verify correct parity setting (8E1)
3. Ensure ground connection between ESP32 and sensor
4. Try shorter wire lengths

Header not found

Symptom: ERROR: Header not found

Solutions:

1. Sensor may not be responding correctly
2. Check baud rate matches (115200)
3. Verify sensor is in measurement mode
4. Power cycle the sensor

Can't upload to ESP32

Symptom: Upload fails or port not found

Solutions:

1. Press and hold BOOT button on ESP32 during upload
2. Check USB cable (must support data, not just power)
3. Install USB drivers for your ESP32 board
4. Try a different USB port

Learning Objectives

This project helps students learn:

Communication Protocols

• Understanding binary serial communication
• Request-response patterns
• Header/state/data/checksum message structure
• Big-endian vs little-endian byte ordering

Embedded Systems Concepts

• UART configuration (baud rate, parity, stop bits)
• GPIO pin assignment and usage
• Non-blocking vs blocking code patterns
• Timeout handling in real-time systems

Data Processing

• Binary data parsing and extraction
• Checksum validation algorithms
• Fixed-point to floating-point conversion
• Byte manipulation with word() function

Arduino/ESP32 Patterns

• Proper use of setup() and loop()
• Non-blocking timing with millis()
• Multiple serial ports (Serial vs Serial1)
• Error handling and debugging techniques

Configuration

Adjusting Read Interval

To change how often the sensor is read, modify the interval constant:

const long interval = 10000;  // Read every 10 seconds (in milliseconds)

Changing GPIO Pins

To use different pins, modify these definitions:

#define PM_SERIAL_RX 39  // Change RX pin
#define PM_SERIAL_TX 32  // Change TX pin

Note: GPIO 39 is input-only on ESP32, so it's ideal for RX.

Project Structure

esp32_NPM_only/
├── src/
│   └── main.cpp           # Main application with extensive comments
├── include/               # Header files (currently empty)
├── lib/                   # Custom libraries (currently empty)
├── test/                  # Unit tests (currently empty)
├── platformio.ini         # PlatformIO configuration
├── CLAUDE.md             # AI assistant guidance
└── README.md             # This file

NextPM Protocol Reference

Concentration Request Command

Byte	Value	Description
0	0x81	Command prefix
1	0x12	Concentration request
2	0x6D	Checksum

Concentration Response (16 bytes)

Bytes	Description	Used?
0-1	Header (0x81 0x12)	✅ For validation
2	State byte	✅ Read but not parsed
3-4	N1.0 particle count	❌ Not used
5-6	N2.5 particle count	❌ Not used
7-8	N10 particle count	❌ Not used
9-10	PM1.0 × 10	✅ Extracted
11-12	PM2.5 × 10	✅ Extracted
13-14	PM10 × 10	✅ Extracted
15	Checksum	✅ Validated

Contributing

This is an educational project. Suggestions for improving code clarity and educational value are welcome!

License

This project is provided for educational purposes.

Acknowledgments

• NextPM sensor documentation
• ESP32 Arduino core community
• Students and educators using this project

---

Questions or Issues?

If you encounter problems or have questions about the code, please open an issue on the repository.