Initial commit: ESP32 NextPM sensor reader
Educational version with comprehensive comments for students. - Reads PM1.0, PM2.5, and PM10 concentrations from NextPM sensor - Uses UART serial communication with checksum validation - Non-blocking timing with millis() - Removed particle counts, kept only mass concentrations - Extensively commented to help students understand serial protocols 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude <noreply@anthropic.com>
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PaulVua
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src/main.cpp
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src/main.cpp
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/*
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* ESP32 NextPM Particulate Matter Sensor Reader
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*
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* This program reads PM (Particulate Matter) concentration data from a NextPM sensor
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* connected to an ESP32 via serial communication (UART).
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*
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* The sensor measures three types of particulate matter:
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* - PM1.0: Particles with diameter < 1.0 micrometers
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* - PM2.5: Particles with diameter < 2.5 micrometers
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* - PM10: Particles with diameter < 10 micrometers
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*
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* Values are reported in µg/m³ (micrograms per cubic meter)
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* Readings are averaged over 60 seconds and updated every 10 seconds
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*/
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#include <Arduino.h>
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/*****************************************************************
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* HARDWARE CONFIGURATION
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*****************************************************************/
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// Serial port definitions
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// The ESP32 has multiple serial ports. We use:
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// - Serial: USB connection for debugging/output (Serial Monitor)
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// - Serial1: UART1 for communicating with the NextPM sensor
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#define serialNPM (Serial1)
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// GPIO pins for sensor communication
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#define PM_SERIAL_RX 39 // Receive data from sensor on GPIO 39
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#define PM_SERIAL_TX 32 // Transmit data to sensor on GPIO 32
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/*****************************************************************
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* TIMING CONFIGURATION
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*****************************************************************/
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// Variables for non-blocking timing
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// We use millis() instead of delay() to avoid blocking the program
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unsigned long previousMillis = 0; // Stores the last time we read the sensor
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const long interval = 10000; // Read every 10 seconds (10000 milliseconds)
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/*****************************************************************
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* DATA STORAGE
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*****************************************************************/
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// Global variables to store the latest PM measurements
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float pm1_ugm3 = 0.0; // PM1.0 concentration in µg/m³
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float pm25_ugm3 = 0.0; // PM2.5 concentration in µg/m³
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float pm10_ugm3 = 0.0; // PM10 concentration in µg/m³
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/*****************************************************************
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* HELPER FUNCTIONS
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*****************************************************************/
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/**
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* Validate the checksum of a 16-byte message from the sensor
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*
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* The NextPM sensor uses a simple checksum algorithm for data integrity:
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* Sum all 16 bytes together, and the result modulo 256 should equal 0.
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*
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* @param data Array of 16 bytes to validate
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* @return true if checksum is valid, false otherwise
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*/
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bool checksum_valid(const uint8_t (&data)[16]) {
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uint8_t sum = 0;
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// Add up all bytes in the message
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for (int i = 0; i < 16; i++) {
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sum += data[i];
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}
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// Valid if sum modulo 256 equals 0
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// (sum % 0x100 is the same as sum % 256)
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return (sum % 0x100 == 0);
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}
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/**
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* Send the command to request concentration data from the sensor
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*
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* The command is a 3-byte sequence:
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* - 0x81: Command prefix (tells sensor a command is coming)
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* - 0x12: Concentration request command code
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* - 0x6D: Checksum byte (makes the sum of all 3 bytes valid)
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*
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* This requests PM values averaged over 1 minute
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*/
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void send_concentration_command() {
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const uint8_t cmd[] = {0x81, 0x12, 0x6D};
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serialNPM.write(cmd, 3); // Send all 3 bytes to the sensor
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}
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/**
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* Print raw byte data in hexadecimal format for debugging
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*
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* This is useful when troubleshooting communication issues with the sensor.
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* Example output: Raw data: 0x81, 0x12, 0x00, 0x1A, ...
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*
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* @param data Array of bytes to print
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* @param size Number of bytes in the array
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*/
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void print_data(uint8_t data[], size_t size) {
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Serial.print("Raw data: ");
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for (size_t i = 0; i < size; i++) {
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Serial.print("0x");
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if (data[i] < 0x10) Serial.print("0"); // Add leading zero for single-digit hex
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Serial.print(data[i], HEX);
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if (i != size - 1) Serial.print(", "); // Add comma between bytes
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}
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Serial.println();
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}
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/*****************************************************************
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* MAIN SENSOR READING FUNCTION
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*****************************************************************/
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/**
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* Read and parse PM concentration data from the NextPM sensor
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*
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* This function performs the following steps:
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* 1. Send a command to the sensor requesting concentration data
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* 2. Wait for and receive the sensor's response (16 bytes total)
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* 3. Validate the data using checksum verification
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* 4. Extract and convert PM values
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* 5. Display results on the serial monitor
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*
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* The sensor response format (16 bytes):
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* [0-1] Header: 0x81 0x12
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* [2] State: Sensor status byte
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* [3-14] Data: 6 values × 2 bytes each (N1, N2.5, N10, PM1, PM2.5, PM10)
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* [15] Checksum: Validation byte
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*/
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void read_concentration() {
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Serial.println("\n--- Reading NextPM Concentrations ---");
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// STEP 1: Send command to sensor
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send_concentration_command();
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// STEP 2: Wait for response with timeout protection
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// The sensor typically responds within 1 second, but we wait up to 3 seconds
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unsigned long timeout = millis();
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while (!serialNPM.available() && millis() - timeout < 3000) {
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delay(10); // Small delay to avoid hogging the CPU
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}
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// Check if we received any data
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if (!serialNPM.available()) {
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Serial.println("ERROR: No response from sensor");
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return; // Exit function if no response
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}
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// STEP 3: Look for the response header (0x81 0x12)
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// The header identifies this as a concentration response message
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const uint8_t header[2] = {0x81, 0x12};
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if (!serialNPM.find(header, 2)) {
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Serial.println("ERROR: Header not found");
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return;
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}
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// STEP 4: Read the state byte
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// This byte contains status information about the sensor
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uint8_t state;
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if (serialNPM.readBytes(&state, 1) != 1) {
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Serial.println("ERROR: Failed to read state");
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return;
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}
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// STEP 5: Read the 12 data bytes
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// These contain 6 values (2 bytes each): N1, N2.5, N10, PM1, PM2.5, PM10
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uint8_t data[12];
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if (serialNPM.readBytes(data, 12) != 12) {
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Serial.println("ERROR: Failed to read data");
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return;
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}
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// STEP 6: Read the checksum byte
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// This is used to verify data integrity
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uint8_t checksum;
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if (serialNPM.readBytes(&checksum, 1) != 1) {
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Serial.println("ERROR: Failed to read checksum");
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return;
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}
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// STEP 7: Reconstruct the complete 16-byte message for validation
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uint8_t full_msg[16];
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full_msg[0] = header[0]; // 0x81
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full_msg[1] = header[1]; // 0x12
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full_msg[2] = state; // State byte
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memcpy(&full_msg[3], data, 12); // Copy 12 data bytes
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full_msg[15] = checksum; // Checksum byte
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// STEP 8: Validate the checksum
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if (!checksum_valid(full_msg)) {
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Serial.println("ERROR: Invalid checksum");
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print_data(full_msg, 16); // Print raw data for debugging
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return;
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}
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// STEP 9: Parse the concentration data from the 12-byte response
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//
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// Data layout in the 12 bytes:
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// Bytes 0-1: N1.0 particle count (we skip this)
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// Bytes 2-3: N2.5 particle count (we skip this)
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// Bytes 4-5: N10 particle count (we skip this)
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// Bytes 6-7: PM1.0 concentration ← We extract this
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// Bytes 8-9: PM2.5 concentration ← We extract this
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// Bytes 10-11: PM10 concentration ← We extract this
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//
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// Each value is a 16-bit unsigned integer (2 bytes) in big-endian format
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// (high byte first, then low byte)
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// Extract PM1.0 concentration (bytes 6-7)
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// word() combines two bytes into a 16-bit integer (high byte, low byte)
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uint16_t pm1_raw = word(data[6], data[7]);
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// Extract PM2.5 concentration (bytes 8-9)
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uint16_t pm25_raw = word(data[8], data[9]);
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// Extract PM10 concentration (bytes 10-11)
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uint16_t pm10_raw = word(data[10], data[11]);
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// STEP 10: Convert raw values to actual concentrations
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// The sensor sends values multiplied by 10 to preserve one decimal place
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// Example: A reading of 25.3 µg/m³ is sent as 253
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// So we divide by 10.0 to get the real value in µg/m³
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pm1_ugm3 = pm1_raw / 10.0;
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pm25_ugm3 = pm25_raw / 10.0;
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pm10_ugm3 = pm10_raw / 10.0;
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// STEP 11: Display the results to the serial monitor
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Serial.println("\n=== Particulate Matter Concentrations ===");
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Serial.print("PM1.0: ");
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Serial.print(pm1_ugm3, 1); // Print with 1 decimal place
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Serial.println(" µg/m³");
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Serial.print("PM2.5: ");
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Serial.print(pm25_ugm3, 1);
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Serial.println(" µg/m³");
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Serial.print("PM10: ");
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Serial.print(pm10_ugm3, 1);
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Serial.println(" µg/m³");
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Serial.println("======================================\n");
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}
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/*****************************************************************
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* ARDUINO SETUP FUNCTION
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*****************************************************************/
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/**
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* Setup function - runs once when the ESP32 starts or resets
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*
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* This function initializes:
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* 1. USB serial communication for debugging/output
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* 2. UART serial communication with the NextPM sensor
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* 3. Waits for the sensor to power up and stabilize
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*/
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void setup() {
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// ===== Initialize USB Serial for debugging =====
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// This allows us to see output in the Arduino Serial Monitor
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Serial.begin(115200); // 115200 baud rate
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delay(2000); // Wait 2 seconds for serial connection to stabilize
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// Print startup message
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Serial.println("\n\n=== NextPM Sensor Reader ===");
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Serial.println("Simplified version - Concentration readings only");
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Serial.println("Averaging: 60 seconds, Update: every 10 seconds\n");
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// ===== Initialize Sensor Serial Communication =====
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// SERIAL_8E1 means:
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// - 8 data bits
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// - Even parity (error checking bit)
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// - 1 stop bit
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// This is the format required by the NextPM sensor
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serialNPM.begin(115200, SERIAL_8E1, PM_SERIAL_RX, PM_SERIAL_TX);
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// Set timeout for serial read operations to 3 seconds
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// If the sensor doesn't respond within 3 seconds, read operations will fail
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serialNPM.setTimeout(3000);
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// ===== Wait for sensor to power up =====
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// The NextPM sensor requires about 15 seconds to initialize after power-on
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// This is critical - reading too early will fail
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Serial.println("Waiting 15 seconds for sensor initialization...");
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delay(15000);
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Serial.println("Sensor ready. Starting measurements...\n");
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}
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/*****************************************************************
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* ARDUINO MAIN LOOP FUNCTION
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*****************************************************************/
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/**
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* Loop function - runs repeatedly after setup() completes
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*
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* This function implements non-blocking timing to read the sensor
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* every 10 seconds without using delay(), which would freeze the program.
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*
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* Non-blocking timing allows the ESP32 to do other tasks between readings
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* (e.g., responding to network requests, processing interrupts, etc.)
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*/
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void loop() {
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// Get the current time in milliseconds since the ESP32 started
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// millis() wraps around after ~49 days, but our math handles this correctly
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unsigned long currentMillis = millis();
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// Check if enough time has passed since the last reading
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// interval = 10000 milliseconds = 10 seconds
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if (currentMillis - previousMillis >= interval) {
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// Update the timestamp for the next reading
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previousMillis = currentMillis;
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// Read and display sensor data
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read_concentration();
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}
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// The loop continues to run, checking the time on every iteration
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// This is much more efficient than using delay() which would block execution
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}
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