# 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](#about-particulate-matter)
- [Features](#features)
- [Hardware Requirements](#hardware-requirements)
- [Wiring Connections](#wiring-connections)
- [Software Requirements](#software-requirements)
- [Installation](#installation)
- [Usage](#usage)
- [Understanding the Code](#understanding-the-code)
- [Expected Output](#expected-output)
- [Troubleshooting](#troubleshooting)
- [Learning Objectives](#learning-objectives)
- [License](#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**
```bash
pip install platformio
```

### Step 2: Clone the Repository

```bash
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:**
```bash
pio project init
```

## Usage

### Building the Project

```bash
pio run
```

### Uploading to ESP32

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

```bash
pio run --target upload
```

### Monitoring Serial Output

View real-time sensor readings:

```bash
pio device monitor
```

Or combine upload and monitor:

```bash
pio run --target upload && pio device monitor
```

**Exit the monitor:** Press `Ctrl+C`

### Cleaning Build Files

```bash
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:

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

### Changing GPIO Pins

To use different pins, modify these definitions:

```cpp
#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.