Meshtastic Environmental Sensor Network Project

Heltec WiFi LoRa 32 + Multiple Sensors

Project Overview

Build a mesh network of environmental monitoring nodes that collect sensor data and share it across the network. Each node can read sensors and display/transmit data to other nodes in the mesh.

Hardware Required

Per Node:

Heltec WiFi LoRa 32 V3 (or V2)
DHT22 Temperature/Humidity Sensor
BMP280 Barometric Pressure Sensor (I2C)
Light Dependent Resistor (LDR)
10kΩ resistor (for LDR)
Jumper wires
Breadboard
LiPo battery (optional for portable operation)
Micro/USB-C cable

Pin Connections

DHT22 Temperature/Humidity Sensor

VCC → 3.3V
GND → GND
Data → GPIO 13

BMP280 Pressure Sensor (I2C)

VCC → 3.3V
GND → GND
SDA → GPIO 21
SCL → GPIO 22

LDR Light Sensor

One leg → 3.3V
Other leg → GPIO 37 (ADC) and 10kΩ resistor to GND

Built-in Components (No wiring needed)

LoRa Radio (SX1276)
OLED Display (128x64)
WiFi/Bluetooth (ESP32)

Software Setup

Step 1: Flash Meshtastic Firmware

Go to https://flasher.meshtastic.org/
Connect Heltec board via USB
Select "Heltec WiFi LoRa 32 V3" (or your version)
Flash the firmware
Configure via Meshtastic app

Step 2: Custom Sensor Code

#include <WiFi.h>
#include <Wire.h>
#include <Adafruit_SSD1306.h>
#include <Adafruit_BMP280.h>
#include <DHT.h>
#include <ArduinoJson.h>

// Pin definitions
#define DHT_PIN 13
#define DHT_TYPE DHT22
#define LDR_PIN 37
#define OLED_SDA 4
#define OLED_SCL 15
#define OLED_RST 16

// Sensor objects
DHT dht(DHT_PIN, DHT_TYPE);
Adafruit_BMP280 bmp;
Adafruit_SSD1306 display(128, 64, &Wire, OLED_RST);

// Data structure
struct SensorData {
  float temperature;
  float humidity;
  float pressure;
  int lightLevel;
  String nodeId;
  unsigned long timestamp;
};

void setup() {
  Serial.begin(115200);
  
  // Initialize I2C for OLED and BMP280
  Wire.begin(OLED_SDA, OLED_SCL);
  
  // Initialize sensors
  dht.begin();
  
  if (!bmp.begin(0x76)) {
    Serial.println("BMP280 not found!");
  }
  
  // Initialize OLED
  if (!display.begin(SSD1306_SWITCHCAPVCC, 0x3c)) {
    Serial.println("OLED not found!");
  }
  
  display.clearDisplay();
  display.setTextSize(1);
  display.setTextColor(WHITE);
  display.setCursor(0, 0);
  display.println("Sensor Node Starting");
  display.display();
  delay(2000);
}

void loop() {
  // Read sensors
  SensorData data = readSensors();
  
  // Display on OLED
  displaySensorData(data);
  
  // Send via Meshtastic (JSON format)
  sendMeshtasticMessage(data);
  
  delay(30000); // Send every 30 seconds
}

SensorData readSensors() {
  SensorData data;
  
  // Read DHT22
  data.temperature = dht.readTemperature();
  data.humidity = dht.readHumidity();
  
  // Read BMP280
  data.pressure = bmp.readPressure() / 100.0; // Convert to hPa
  
  // Read LDR
  int rawLight = analogRead(LDR_PIN);
  data.lightLevel = map(rawLight, 0, 4095, 0, 100);
  
  // Add metadata
  data.nodeId = WiFi.macAddress();
  data.timestamp = millis();
  
  return data;
}

void displaySensorData(SensorData data) {
  display.clearDisplay();
  display.setCursor(0, 0);
  
  display.println("SENSOR NODE");
  display.println("------------");
  display.print("Temp: ");
  display.print(data.temperature, 1);
  display.println("C");
  
  display.print("Humid: ");
  display.print(data.humidity, 1);
  display.println("%");
  
  display.print("Press: ");
  display.print(data.pressure, 1);
  display.println(" hPa");
  
  display.print("Light: ");
  display.print(data.lightLevel);
  display.println("%");
  
  display.display();
}

void sendMeshtasticMessage(SensorData data) {
  // Create JSON message
  StaticJsonDocument<200> doc;
  doc["node"] = data.nodeId;
  doc["temp"] = data.temperature;
  doc["humid"] = data.humidity;
  doc["press"] = data.pressure;
  doc["light"] = data.lightLevel;
  doc["time"] = data.timestamp;
  
  String jsonString;
  serializeJson(doc, jsonString);
  
  // Send via Serial to Meshtastic (if using custom firmware)
  Serial.println("SENSOR_DATA:" + jsonString);
}

Project Extensions

1. Data Logging

Add SD card module to log sensor data
Store data with timestamps for analysis

2. Alerting System

Set thresholds for temperature, humidity, etc.
Send alert messages when limits exceeded

3. Web Dashboard

Create simple web server on one node
Display real-time data from all nodes in network

4. GPS Integration

Add GPS module for location data
Create mobile environmental monitoring stations

5. Power Management

Implement deep sleep between readings
Solar charging for outdoor deployment

Learning Objectives

Technical Skills

Mesh Networking: Understanding decentralized communication
Sensor Integration: Multiple sensor types and protocols
Data Serialization: JSON formatting for transmission
Display Programming: OLED graphics and text
Power Management: Battery operation considerations

Network Concepts

Mesh Topology: How messages route through network
Data Redundancy: Multiple paths for reliability
Range Testing: Understanding LoRa propagation
Network Scaling: Adding/removing nodes dynamically

Experiments to Try

1. Range Testing

Deploy nodes at increasing distances
Measure packet success rates
Map coverage area

2. Network Resilience

Remove nodes and observe mesh healing
Test message routing through intermediary nodes

3. Data Analysis

Collect environmental data over time
Compare readings from different locations
Identify patterns and anomalies

4. Performance Optimization

Adjust transmission intervals
Optimize message size
Balance battery life vs data frequency

Assessment Ideas

Students document network topology
Compare sensor readings between nodes
Analyze message routing efficiency
Design custom sensor integrations
Present findings on mesh network behavior

Safety Notes

Use appropriate voltage levels (3.3V for most sensors)
Double-check wiring before powering on
Handle LiPo batteries safely
Follow local regulations for LoRa frequency usage

This project combines practical electronics, networking concepts, and real-world data collection while demonstrating the power of mesh networks for IoT applications.

Meshtastic Environmental Monitor