🔌 Arduino MQTT Bridge

A powerful tool for connecting your Arduino devices to MQTT brokers. This bridge enables bidirectional communication between Arduino serial interfaces and MQTT protocols, perfect for IoT applications.

✨ Features

• 🔄 Bidirectional communication between Arduino and MQTT
• ⚙️ Simple configuration through CLI
• 🔒 Support for MQTT authentication
• 📊 Automatic JSON parsing for sensor data
• 🧩 Customizable MQTT topics
• 🔧 Easy serial port configuration

📦 Installation

# Install globally
npm install -g arduino-mqtt

# Or use directly with npx
npx arduino-mqtt config

🚀 Quick Start

1. Configure the bridge

# Interactive setup
arduino-mqtt config

# Or set individual values
arduino-mqtt set port COM7
arduino-mqtt set baud 9600
arduino-mqtt set ip mqtt://localhost:1883

2. Start the bridge

# Start the MQTT-Arduino bridge
arduino-mqtt run

3. Stop the bridge

# Press Ctrl+C or run
arduino-mqtt stop

🔧 Configuration Options

| Parameter | Description | Default Value | |-----------|-------------|---------------| | port | Serial port connected to Arduino | COM7 | | baud | Baud rate for serial communication | 9600 | | ip | MQTT broker address | mqtt://localhost:1883 | | commandsTopic | Topic to receive commands for Arduino | arduino/commands | | sensorsTopic | Topic to publish Arduino sensor data | arduino/sensors | | username | MQTT broker username (if required) | | | password | MQTT broker password (if required) | |

📝 Command Reference

| Command | Description | |---------|-------------| | arduino-mqtt config | Interactive configuration wizard | | arduino-mqtt run | Start the bridge | | arduino-mqtt stop | Stop the bridge | | arduino-mqtt set <key> <value> | Update specific configuration | | arduino-mqtt get [key] | View configuration (all or specific key) |

📊 Data Flow

Arduino → MQTT

• Serial data from Arduino is read line by line
• JSON data is automatically parsed and published to the sensorsTopic
• Non-JSON data is published to sensorsTopic/raw

MQTT → Arduino

• Messages received on commandsTopic are sent directly to Arduino
• Each command is terminated with a newline character

🔌 Arduino Code Examples

Basic LED Control Example

#include <ArduinoJson.h>  // Include ArduinoJson library (install from Library Manager)

// Define pins
#define LED1_PIN 13  // Built-in LED
#define LED2_PIN 12
#define LED3_PIN 11
#define LED4_PIN 10

// Define JSON document size based on your needs
#define JSON_DOC_SIZE 256

void setup() {
  Serial.begin(9600);
  
  // Initialize LED pins
  pinMode(LED1_PIN, OUTPUT);
  pinMode(LED2_PIN, OUTPUT);
  pinMode(LED3_PIN, OUTPUT);
  pinMode(LED4_PIN, OUTPUT);
  
  delay(1000);  // Give serial connection time to stabilize
}

void loop() {
  // Read and process commands from MQTT
  if (Serial.available() > 0) {
    String command = Serial.readStringUntil('\n');
    processCommand(command);
  }
  
  // Send sensor data to MQTT
  sendSensorData();
  
  delay(5000);  // Send every 5 seconds
}

// Process incoming commands, including simple key-value pairs
void processCommand(String command) {
  // Check if command has a key-value format (key=value)
  int separatorPos = command.indexOf('=');
  
  if (separatorPos > 0) {
    // Extract key and value
    String key = command.substring(0, separatorPos);
    String value = command.substring(separatorPos + 1);
    
    // Trim whitespace
    key.trim();
    value.trim();
    
    // Convert key to lowercase for case-insensitive comparison
    key.toLowerCase();
    
    // Check for LED commands (l1, l2, l3, l4)
    if (key == "l1" || key == "led1") {
      setLedState(LED1_PIN, value);
    } 
    else if (key == "l2" || key == "led2") {
      setLedState(LED2_PIN, value);
    }
    else if (key == "l3" || key == "led3") {
      setLedState(LED3_PIN, value);
    }
    else if (key == "l4" || key == "led4") {
      setLedState(LED4_PIN, value);
    }
    else if (key == "all") {
      // Set all LEDs to the same state
      setLedState(LED1_PIN, value);
      setLedState(LED2_PIN, value);
      setLedState(LED3_PIN, value);
      setLedState(LED4_PIN, value);
    }
  }
  else {
    // Handle legacy commands like "LED_ON" or "LED_OFF"
    if (command == "LED_ON") {
      digitalWrite(LED1_PIN, HIGH);
    } 
    else if (command == "LED_OFF") {
      digitalWrite(LED1_PIN, LOW);
    }
  }
}

// Set LED state based on various input formats
void setLedState(int pin, String state) {
  // Convert to lowercase for case-insensitive comparison
  state.toLowerCase();
  
  // Check for various ON representations
  if (state == "on" || state == "true" || state == "1" || state == "high") {
    digitalWrite(pin, HIGH);
  }
  // Check for various OFF representations
  else if (state == "off" || state == "false" || state == "0" || state == "low") {
    digitalWrite(pin, LOW);
  }
  // Handle numeric brightness for PWM pins
  else {
    // Try to parse as integer for PWM value
    int brightness = state.toInt();
    if (brightness > 0 || state == "0") {
      // Constrain value to valid PWM range
      brightness = constrain(brightness, 0, 255);
      analogWrite(pin, brightness);
    }
  }
}

// Send sensor data as JSON to MQTT
void sendSensorData() {
  StaticJsonDocument<JSON_DOC_SIZE> doc;
  
  // Add sensor readings
  doc["temperature"] = readTemperature();
  doc["humidity"] = readHumidity();
  doc["light"] = analogRead(A2);
  doc["uptime"] = millis() / 1000;
  
  // Add LED states
  doc["led1"] = digitalRead(LED1_PIN);
  doc["led2"] = digitalRead(LED2_PIN);
  doc["led3"] = digitalRead(LED3_PIN);
  doc["led4"] = digitalRead(LED4_PIN);
  
  // Serialize and send JSON
  serializeJson(doc, Serial);
  Serial.println();  // Add newline to complete the message
}

// Example sensor reading functions
float readTemperature() {
  return analogRead(A0) * 0.48;  // Example conversion - replace with actual sensor code
}

float readHumidity() {
  return analogRead(A1) * 0.1;  // Example conversion - replace with actual sensor code
}

Advanced DHT Sensor Example

#include <ArduinoJson.h>
#include <DHT.h>

#define DHTPIN 2          // Digital pin connected to the DHT sensor
#define DHTTYPE DHT22     // DHT 22 (AM2302)
#define RELAY_PIN 4       // Digital pin connected to relay
#define JSON_DOC_SIZE 384 // Larger for more complex JSON

DHT dht(DHTPIN, DHTTYPE);
bool autoMode = true;
float tempThreshold = 25.0; // Temperature threshold in °C

void setup() {
  Serial.begin(9600);
  pinMode(RELAY_PIN, OUTPUT);
  dht.begin();
  delay(2000); // DHT sensor stabilization
  
  // Initial status report
  sendStatusReport();
}

void loop() {
  // Handle incoming commands
  if (Serial.available() > 0) {
    String command = Serial.readStringUntil('\n');
    processCommand(command);
  }
  
  // Auto mode logic
  if (autoMode) {
    float temperature = dht.readTemperature();
    if (!isnan(temperature)) {
      if (temperature > tempThreshold) {
        digitalWrite(RELAY_PIN, HIGH); // Turn on cooling
      } else {
        digitalWrite(RELAY_PIN, LOW);  // Turn off cooling
      }
    }
  }
  
  // Send regular sensor updates
  static unsigned long lastSendTime = 0;
  if (millis() - lastSendTime > 10000) { // Every 10 seconds
    sendStatusReport();
    lastSendTime = millis();
  }
}

void processCommand(String command) {
  // Try to parse as JSON first
  StaticJsonDocument<JSON_DOC_SIZE> doc;
  DeserializationError error = deserializeJson(doc, command);
  
  if (!error) {
    // JSON command handling
    if (doc.containsKey("relay")) {
      digitalWrite(RELAY_PIN, doc["relay"] ? HIGH : LOW);
      autoMode = false; // Disable auto mode when manually controlled
    }
    
    if (doc.containsKey("auto")) {
      autoMode = doc["auto"];
    }
    
    if (doc.containsKey("threshold")) {
      tempThreshold = doc["threshold"];
    }
    
    // Send confirmation
    sendStatusReport();
  }
  else {
    // Key-value command handling
    int separatorPos = command.indexOf('=');
    if (separatorPos > 0) {
      String key = command.substring(0, separatorPos);
      String value = command.substring(separatorPos + 1);
      key.trim();
      value.trim();
      key.toLowerCase();
      
      if (key == "relay") {
        value.toLowerCase();
        bool state = (value == "on" || value == "true" || value == "1" || value == "high");
        digitalWrite(RELAY_PIN, state ? HIGH : LOW);
        autoMode = false;
      }
      else if (key == "auto") {
        value.toLowerCase();
        autoMode = (value == "on" || value == "true" || value == "1");
      }
      else if (key == "threshold") {
        tempThreshold = value.toFloat();
      }
      
      // Send confirmation
      sendStatusReport();
    }
  }
}

void sendStatusReport() {
  StaticJsonDocument<JSON_DOC_SIZE> doc;
  
  // Read sensor data
  float h = dht.readHumidity();
  float t = dht.readTemperature();
  
  // Add sensor readings
  doc["humidity"] = isnan(h) ? "error" : h;
  doc["temperature"] = isnan(t) ? "error" : t;
  
  // Add system state
  doc["relay"] = digitalRead(RELAY_PIN);
  doc["auto_mode"] = autoMode;
  doc["threshold"] = tempThreshold;
  doc["uptime"] = millis() / 1000;
  
  // Serialize and send
  serializeJson(doc, Serial);
  Serial.println();
}

Battery Powered Sensor Node Example

#include <ArduinoJson.h>
#include <LowPower.h>

#define BATTERY_PIN A0
#define SOIL_MOISTURE_PIN A1
#define LIGHT_SENSOR_PIN A2
#define JSON_DOC_SIZE 256

// Configuration with defaults
int sleepCycles = 75;      // 75 cycles × 8s = 10 minutes
bool ledEnabled = false;   // LED indicators (disable to save power)
int sensorThreshold = 30;  // Soil moisture threshold percent

void setup() {
  Serial.begin(9600);
  pinMode(LED_BUILTIN, OUTPUT);
  digitalWrite(LED_BUILTIN, LOW); // Ensure LED is off
  
  delay(1000); // Allow serial to initialize
  sendSensorData(); // Initial reading
}

void loop() {
  // Check for config commands
  if (Serial.available() > 0) {
    String command = Serial.readStringUntil('\n');
    processCommand(command);
  }
  
  // Flash LED indicator if enabled
  if (ledEnabled) {
    digitalWrite(LED_BUILTIN, HIGH);
    delay(50);
    digitalWrite(LED_BUILTIN, LOW);
  }
  
  // Send data before sleeping
  sendSensorData();
  
  // Enter power-down mode for 8s × sleepCycles
  Serial.flush(); // Make sure all serial data is sent
  for (int i = 0; i < sleepCycles; i++) {
    LowPower.powerDown(SLEEP_8S, ADC_OFF, BOD_OFF);
  }
}

void processCommand(String command) {
  // Find key=value separator
  int separatorPos = command.indexOf('=');
  
  if (separatorPos > 0) {
    String key = command.substring(0, separatorPos);
    String value = command.substring(separatorPos + 1);
    
    key.trim();
    value.trim();
    key.toLowerCase();
    
    if (key == "sleep") {
      int cycles = value.toInt();
      if (cycles > 0) {
        sleepCycles = cycles;
      }
    }
    else if (key == "led") {
      value.toLowerCase();
      ledEnabled = (value == "on" || value == "true" || value == "1");
    }
    else if (key == "threshold") {
      int threshold = value.toInt();
      if (threshold >= 0 && threshold <= 100) {
        sensorThreshold = threshold;
      }
    }
    
    // Send updated configuration
    StaticJsonDocument<JSON_DOC_SIZE> doc;
    doc["config_sleep"] = sleepCycles;
    doc["config_led"] = ledEnabled;
    doc["config_threshold"] = sensorThreshold;
    serializeJson(doc, Serial);
    Serial.println();
  }
}

void sendSensorData() {
  StaticJsonDocument<JSON_DOC_SIZE> doc;
  
  // Read battery voltage (example calculation for 3.7V LiPo through voltage divider)
  int batteryRaw = analogRead(BATTERY_PIN);
  float batteryVoltage = batteryRaw * (5.0 / 1023.0) * 2.0; // Example voltage divider calculation
  int batteryPercent = map(batteryRaw, 614, 820, 0, 100);   // Map raw values to percentage (calibrate these values)
  batteryPercent = constrain(batteryPercent, 0, 100);
  
  // Read soil moisture (example)
  int soilRaw = analogRead(SOIL_MOISTURE_PIN);
  int soilPercent = map(soilRaw, 0, 1023, 100, 0);  // Inverted - higher resistance = drier soil
  
  // Read light level (example)
  int lightRaw = analogRead(LIGHT_SENSOR_PIN);
  int lightPercent = map(lightRaw, 0, 1023, 0, 100);
  
  // Populate JSON
  doc["device_id"] = "soil_sensor_1";
  doc["battery_v"] = batteryVoltage;
  doc["battery_pct"] = batteryPercent;
  doc["moisture"] = soilPercent;
  doc["light"] = lightPercent;
  doc["needs_water"] = soilPercent < sensorThreshold;
  
  // Serialize and send
  serializeJson(doc, Serial);
  Serial.println();
}

🖥️ Testing & Development Tools

🔌 PuTTY Serial Testing

PuTTY is a versatile tool for testing serial communication with your Arduino:

Basic PuTTY Setup

1. Download and install PuTTY
2. Configure PuTTY for serial connection:
   • Connection type: Serial
   • Serial line: COM8 (or your Arduino port)
   • Speed: 9600 (match Arduino baud rate)
   • Under Terminal → Local echo: Force on
   • Under Terminal → Local line editing: Force on

PuTTY Testing Examples

Testing Arduino Output:

1. Open PuTTY with the above configuration
2. Messages from the Arduino will appear in the terminal
3. You should see JSON data like:

   {"temperature":23.5,"humidity":48,"light":512}

Sending Commands to Arduino:

1. Type a command in PuTTY window and press Enter
2. Example commands:

   LED_ON
   l1=on
   l2=off
   l3=128
   {"led1":true,"led2":false}

Using for Serial Bridge Testing:

1. Install a COM port emulator like com0com
2. Create a virtual port pair (COM7-COM8)
3. Configure arduino-mqtt bridge to use COM7
4. Connect PuTTY to COM8
5. Start the bridge with arduino-mqtt run
6. Type sample JSON data into PuTTY:

   {"temperature":23.5,"humidity":55,"light":890}

7. This data will be forwarded to your MQTT broker

🔧 Arduino IDE Serial Monitor

The Arduino IDE's built-in Serial Monitor is perfect for quick testing:

Basic Setup

1. Connect your Arduino to your computer
2. Open Arduino IDE
3. Select the correct board and port
4. Open Serial Monitor (Tools → Serial Monitor or Ctrl+Shift+M)
5. Set baud rate to match your Arduino (e.g., 9600)
6. Set line ending to "Newline"

Testing Examples

Monitoring Arduino Output:

1. Upload a sketch that sends JSON data (like examples above)
2. Open Serial Monitor
3. You'll see the JSON output:

   {"temperature":22.8,"humidity":45,"led1":1,"led2":0}

Sending Commands:

1. Type commands in the input field at the top of Serial Monitor
2. Press "Send" or Enter
3. Example commands:

   l1=on
   l1=off
   l2=128

4. Verify the Arduino responds correctly (LEDs change, status updates)

Testing While Bridge is Running:

1. Upload your sketch to Arduino
2. Start the bridge in a terminal: arduino-mqtt run
3. Open Arduino IDE Serial Monitor
4. You'll see a warning about port being in use - this is expected
5. Close Serial Monitor and interact with Arduino via MQTT clients

📊 MQTTX Client

MQTTX is a free, cross-platform MQTT client with a user-friendly interface:

Setting up MQTTX

1. Download MQTTX for your platform
2. Install and open the application
3. Click "+" to add a new connection
4. Configure connection:
   • Name: Arduino Bridge
   • Host: localhost (or your MQTT broker address)
   • Port: 1883 (default MQTT port)
   • Add client ID, username, and password if required

MQTTX Testing Examples

Subscribing to Arduino Data:

1. After connecting, click "New Subscription"
2. Topic: arduino/sensors (or your configured sensorsTopic)
3. QoS: 0
4. Click "Confirm"
5. You should see incoming data from your Arduino as JSON messages

Sending Commands to Arduino:

1. In "Publish" section:
   • Topic: arduino/commands (or your configured commandsTopic)
   • QoS: 0
   • Retain: false (usually)
2. Type a command in the payload field:

   l1=on

3. Click "Send"
4. Arduino should respond by turning on the LED
5. Try other commands:

   l1=off
   led2=128
   all=high

6. For JSON commands, select "JSON" format in MQTTX and enter:

   {
     "led1": true,
     "led2": false,
     "threshold": 25
   }

Testing Complex Scenarios:

1. Subscribe to multiple topics:
   • arduino/sensors (for main data)
   • arduino/sensors/raw (for non-JSON data)
   • arduino/status (if your sketch publishes status)
2. Use the MQTTX history feature to save frequently used commands
3. Create a workspace with frequently used topics
4. Test message retention by enabling "Retain" for configuration commands

🔄 Combined Testing Workflow

For a complete test setup, try this workflow:

1. Setup:

   • Connect Arduino or set up COM port emulator
   • Configure arduino-mqtt with arduino-mqtt config
   • Start the bridge with arduino-mqtt run
   • Open MQTTX and connect to your broker
   • Subscribe to arduino/sensors topic

2. Testing Arduino → MQTT Flow:

   • Open Arduino IDE Serial Monitor (or PuTTY) to view/send serial data
   • Send data via Serial Monitor or have your Arduino sketch send data
   • Verify the data appears in MQTTX

3. Testing MQTT → Arduino Flow:

   • In MQTTX, publish a command to arduino/commands
   • Verify the Arduino responds correctly (LEDs change state)
   • Check the Arduino's JSON response to confirm changes

4. Troubleshooting with Serial Monitor:

   • Stop the bridge
   • Open Arduino IDE Serial Monitor
   • Test commands directly to isolate issues
   • Close Serial Monitor and restart the bridge

🧰 Troubleshooting

Common Issues:

• Serial port not found: Ensure your Arduino is connected and the port is correct
• MQTT connection failed: Verify broker address and credentials
• No data from Arduino: Check baud rate matches your Arduino sketch
• Garbled data: Ensure line endings are consistent (use \n or \r\n)
• JSON parsing errors: Verify your Arduino is sending valid JSON data
• Commands not working: Make sure newline characters are being sent after commands
• Bridge starts but no data flows: Confirm topics match between bridge and MQTT client

Advanced Troubleshooting:

• Use the bridge's raw topic (sensorsTopic/raw) to see unparsed data
• Enable verbose logging in your MQTT broker (if available)
• Test with simple text commands before trying JSON commands
• Use arduino-mqtt get to verify your configuration settings
• Check Arduino serial buffer size if sending large JSON payloads

📄 License

This project is licensed under the MIT License - see the LICENSE file for details.

🤝 Contributing

Contributions are welcome! Feel free to open issues or submit pull requests.

🙏 Acknowledgements

• SerialPort for the robust serial communication
• await-mqtt for the Promise-based async/await MQTT client implementation
• MQTT.js for the MQTT client implementation
• ArduinoJson for efficient JSON parsing on Arduino
• Clack for the beautiful CLI interface