Arduino UNO R4 - DIYables Bluetooth App Monitor
Overview
The Bluetooth Monitor example provides a wireless serial monitor accessible through the DIYables Bluetooth STEM app. Designed for Arduino UNO R4 WiFi using BLE (Bluetooth Low Energy) to stream real-time status messages, debug output, and sensor readings wirelessly to your smartphone. Also receive text commands from the app. Perfect for wireless debugging, remote monitoring, and system logging.
Note: The Arduino UNO R4 WiFi only supports BLE (Bluetooth Low Energy). It does not support Classic Bluetooth. The DIYables Bluetooth App supports both BLE and Classic Bluetooth on Android, and BLE on iOS. Since this board uses BLE, the app works on both Android and iOS.
Features
- Wireless Serial Monitor: Stream text messages to your phone
- Two-Way Communication: Send commands from app to Arduino
- Real-Time Streaming: Continuous output like Serial Monitor
- Command Handling: Process text commands from the app
- Works on Android & iOS: BLE is supported on both platforms
- No Pairing Required: BLE auto-connects without manual pairing
- Low Power: BLE consumes less power than Classic Bluetooth
Hardware Preparation
Or you can buy the following kits:
| 1 | × | DIYables STEM V4 IoT Starter Kit (Arduino included) | |
| 1 | × | DIYables Sensor Kit (30 sensors/displays) | |
| 1 | × | DIYables Sensor Kit (18 sensors/displays) |
Disclosure: Some of the links provided in this section are Amazon affiliate links. We may receive a commission for any purchases made through these links at no additional cost to you.
Additionally, some of these links are for products from our own brand, DIYables .
Additionally, some of these links are for products from our own brand, DIYables .
Arduino UNO R4 WiFi Code
Detailed Instructions
Follow these instructions step by step:
- If this is your first time using the Arduino UNO R4 WiFi, refer to the Arduino UNO R4 WiFi getting started guide.
- Connect the Arduino UNO R4 WiFi board to your computer using a USB cable.
- Launch the Arduino IDE on your computer.
- Select Arduino UNO R4 WiFi board and the appropriate COM port.
- Navigate to the Libraries icon on the left bar of the Arduino IDE.
- Search "DIYables Bluetooth", then find the DIYables Bluetooth library by DIYables
- Click Install button to install the library.
- You will be asked for installing some other library dependencies
- Click Install All button to install all library dependencies.
BLE Code
- On Arduino IDE, Go to File Examples DIYables Bluetooth ArduinoBLE_Monitor example, or copy the above code and paste it to the editor of Arduino IDE
/*
* DIYables Bluetooth Library - Bluetooth Monitor Example
* Works with DIYables Bluetooth STEM app on Android and iOS
*
* This example demonstrates the Bluetooth Monitor feature:
* - Send real-time status messages to the mobile app
* - Display system information and sensor readings
* - Receive and process commands from the app
* - Perfect for debugging and system monitoring
*
* Compatible Boards:
* - Arduino UNO R4 WiFi
* - Arduino Nano 33 BLE / BLE Sense
* - Arduino Nano 33 IoT
* - Arduino MKR WiFi 1010
* - Arduino Nano RP2040 Connect
* - Any board supporting the ArduinoBLE library
*
* Setup:
* 1. Upload the sketch to your Arduino
* 2. Open Serial Monitor to see connection status
* 3. Use DIYables Bluetooth App to connect and view monitor output
*
* Tutorial: https://diyables.io/bluetooth-app
* Author: DIYables
*/
#include <DIYables_BluetoothServer.h>
#include <DIYables_BluetoothMonitor.h>
#include <platforms/DIYables_ArduinoBLE.h>
// BLE Configuration
const char* DEVICE_NAME = "Arduino_Monitor";
const char* SERVICE_UUID = "19B10000-E8F2-537E-4F6C-D104768A1214";
const char* TX_UUID = "19B10001-E8F2-537E-4F6C-D104768A1214";
const char* RX_UUID = "19B10002-E8F2-537E-4F6C-D104768A1214";
// Create Bluetooth instances
DIYables_ArduinoBLE bluetooth(DEVICE_NAME, SERVICE_UUID, TX_UUID, RX_UUID);
DIYables_BluetoothServer bluetoothServer(bluetooth);
// Create Monitor app instance
DIYables_BluetoothMonitor bluetoothMonitor;
// Variables for demo
unsigned long lastUpdate = 0;
const unsigned long UPDATE_INTERVAL = 3000; // Send update every 3 seconds
int messageCount = 0;
bool ledState = false;
void setup() {
Serial.begin(9600);
while (!Serial);
Serial.println("DIYables Bluetooth - Monitor Example");
// Initialize built-in LED
pinMode(LED_BUILTIN, OUTPUT);
digitalWrite(LED_BUILTIN, LOW);
// Initialize Bluetooth server with platform-specific implementation
bluetoothServer.begin();
// Add monitor app to server
bluetoothServer.addApp(&bluetoothMonitor);
// Set up connection event callbacks
bluetoothServer.setOnConnected([]() {
Serial.println("Bluetooth connected!");
bluetoothMonitor.send("=== Arduino Monitor Connected ===");
bluetoothMonitor.send("System Ready");
bluetoothMonitor.send("Type HELP for available commands");
bluetoothMonitor.send("");
});
bluetoothServer.setOnDisconnected([]() {
Serial.println("Bluetooth disconnected!");
});
// Set up message handler for incoming commands
bluetoothMonitor.onMonitorMessage([](const String& message) {
Serial.print("Received command: ");
Serial.println(message);
handleCommand(message);
});
Serial.println("Waiting for Bluetooth connection...");
}
void handleCommand(const String& cmd) {
if (cmd == "HELP") {
bluetoothMonitor.send("Available Commands:");
bluetoothMonitor.send(" LED_ON - Turn LED on");
bluetoothMonitor.send(" LED_OFF - Turn LED off");
bluetoothMonitor.send(" STATUS - Show system status");
bluetoothMonitor.send(" CLEAR - Clear monitor (if supported)");
bluetoothMonitor.send(" HELP - Show this help");
}
else if (cmd == "LED_ON") {
digitalWrite(LED_BUILTIN, HIGH);
ledState = true;
bluetoothMonitor.send("✓ LED turned ON");
}
else if (cmd == "LED_OFF") {
digitalWrite(LED_BUILTIN, LOW);
ledState = false;
bluetoothMonitor.send("✓ LED turned OFF");
}
else if (cmd == "STATUS") {
showStatus();
}
else if (cmd == "CLEAR") {
// App should handle clearing the display
bluetoothMonitor.send("");
}
else {
bluetoothMonitor.send("✗ Unknown command: " + cmd);
bluetoothMonitor.send("Type HELP for available commands");
}
}
void showStatus() {
bluetoothMonitor.send("=== System Status ===");
// LED Status
bluetoothMonitor.send("LED State: " + String(ledState ? "ON" : "OFF"));
// Uptime
unsigned long uptime = millis() / 1000;
bluetoothMonitor.send("Uptime: " + String(uptime / 3600) + "h " + String((uptime % 3600) / 60) + "m " + String(uptime % 60) + "s");
// Free Memory (approximate for AVR)
#ifdef __AVR__
extern int __heap_start, *__brkval;
int freeMemory = (int) &freeMemory - (__brkval == 0 ? (int) &__heap_start : (int) __brkval);
bluetoothMonitor.send("Free Memory: " + String(freeMemory) + " bytes");
#endif
// Messages sent
bluetoothMonitor.send("Messages Sent: " + String(messageCount));
bluetoothMonitor.send("====================");
}
void sendPeriodicUpdate() {
messageCount++;
// Example of different message types
if (messageCount % 3 == 0) {
// Send status update
bluetoothMonitor.send("[INFO] Heartbeat #" + String(messageCount));
}
else if (messageCount % 5 == 0) {
// Send simulated sensor reading
int sensorValue = random(0, 1024);
bluetoothMonitor.send("[SENSOR] Reading: " + String(sensorValue) + " (random demo value)");
}
else {
// Send timestamp
bluetoothMonitor.send("[TIME] Uptime: " + String(millis() / 1000) + "s");
}
// Optionally log to Serial as well
Serial.print("Sent update #");
Serial.println(messageCount);
}
void loop() {
// Handle Bluetooth server communications
bluetoothServer.loop();
// Send periodic updates (only when connected)
if (bluetooth.isConnected() && millis() - lastUpdate >= UPDATE_INTERVAL) {
lastUpdate = millis();
sendPeriodicUpdate();
}
delay(10);
}
- Click Upload button on Arduino IDE to upload code to Arduino UNO R4 WiFi
- Open the Serial Monitor
- Check out the result on Serial Monitor. It looks like the below:
COM6
DIYables Bluetooth - Monitor Example
Waiting for Bluetooth connection...
Autoscroll
Clear output
9600 baud
Newline
Mobile App
Note: The DIYables Bluetooth App supports both BLE and Classic Bluetooth on Android, and BLE on iOS. Since the Arduino UNO R4 WiFi uses BLE, the app works on both Android and iOS. No manual pairing is needed for BLE — just scan and connect.
- Open the DIYables Bluetooth App
- When opening the app for the first time, it will ask for permissions. Please grant the following:
- Nearby Devices permission (Android 12+) / Bluetooth permission (iOS) - required to scan and connect to Bluetooth devices
- Location permission (Android 11 and below only) - required by older Android versions to scan for BLE devices
- Make sure Bluetooth is turned on on your phone
- On the home screen, tap the Connect button. The app will scan for BLE devices.
- Find and tap "Arduino_Monitor" in the scan results to connect.
- Once connected, the app automatically goes back to the home screen. Select the Monitor app from the app menu.
Note: You can tap the settings icon on the home screen to hide/show apps on the home screen. For more details, see the DIYables Bluetooth App User Manual.
- You will see status messages streaming in the monitor display
- Type LED_ON in the input field and tap Send — the built-in LED on the Arduino UNO R4 WiFi will turn ON, and the monitor will display a confirmation message
Now look back at the Serial Monitor on Arduino IDE. You will see:
COM6
Bluetooth connected!
Sent update #1
Sent update #2
Sent update #3
Autoscroll
Clear output
9600 baud
Newline
Creative Customization - Adapt the Code to Your Project
Send Messages
// Send text messages to the app
bluetoothMonitor.send("System started");
bluetoothMonitor.send("Temperature: " + String(temp, 1) + " °C");
bluetoothMonitor.send("[ERROR] Sensor disconnected!");
Handle Incoming Commands
Use the onMonitorMessage() callback to receive commands typed in the Monitor app and react to them:
bluetoothMonitor.onMonitorMessage([](const String& message) {
Serial.print("Received: ");
Serial.println(message);
if (message == "HELP") {
bluetoothMonitor.send("Commands: LED_ON, LED_OFF, STATUS, HELP");
} else if (message == "LED_ON") {
digitalWrite(LED_BUILTIN, HIGH);
bluetoothMonitor.send("LED turned ON");
} else if (message == "LED_OFF") {
digitalWrite(LED_BUILTIN, LOW);
bluetoothMonitor.send("LED turned OFF");
} else if (message == "STATUS") {
bluetoothMonitor.send("Uptime: " + String(millis() / 1000) + "s");
bluetoothMonitor.send("LED: " + String(digitalRead(LED_BUILTIN) ? "ON" : "OFF"));
} else {
bluetoothMonitor.send("Unknown command: " + message);
}
});
You can add as many custom commands as you need by adding more else if blocks. For example, add RELAY_ON / RELAY_OFF to control a relay, or READ to trigger a sensor reading — any word you type in the app becomes a command.
Programming Examples
Sensor Status Streaming
void loop() {
bluetoothServer.loop();
static unsigned long lastUpdate = 0;
if (bluetooth.isConnected() && millis() - lastUpdate >= 3000) {
lastUpdate = millis();
int light = analogRead(A0);
float voltage = analogRead(A1) * 5.0 / 1023.0;
bluetoothMonitor.send("[SENSOR] Light: " + String(map(light, 0, 1023, 0, 100)) + "%");
bluetoothMonitor.send("[SENSOR] Voltage: " + String(voltage, 2) + "V");
bluetoothMonitor.send("[INFO] Uptime: " + String(millis() / 1000) + "s");
}
delay(10);
}
Event-Based Logging
const int BUTTON_PIN = 7;
int lastButtonState = HIGH;
void loop() {
bluetoothServer.loop();
int buttonState = digitalRead(BUTTON_PIN);
if (buttonState != lastButtonState) {
lastButtonState = buttonState;
if (buttonState == LOW) {
bluetoothMonitor.send("[EVENT] Button pressed!");
} else {
bluetoothMonitor.send("[EVENT] Button released");
}
}
delay(10);
}
Troubleshooting
Common Issues
1. Cannot find the device in the app
- Make sure the Arduino UNO R4 WiFi is powered on and the sketch is uploaded
- Ensure your phone's Bluetooth is enabled
- On Android 11 and below, also enable Location services
2. No messages appearing in the app
- Verify bluetoothMonitor.send() is being called
- Check that bluetoothServer.loop() is in the main loop
- Confirm connection in Serial Monitor
3. Messages are delayed
- Reduce the update interval for more frequent messages
- Avoid sending too many messages too quickly (BLE has bandwidth limits)
4. Commands from app not received
- Verify the onMonitorMessage callback is set up
- Check Serial Monitor for received command output
5. Connection drops frequently
- Move closer to the Arduino (reduce distance)
- Ensure stable USB power supply
6. Upload fails or board not recognized
- Install the latest Arduino UNO R4 board package via Board Manager
- Try a different USB cable or port
Project Ideas
- Wireless debug console
- Sensor data logger
- System health monitor
- Event notification system
- Remote command interface
Next Steps
After mastering the Bluetooth Monitor example, try:
- Bluetooth Chat - For interactive two-way messaging
- Bluetooth Table - For structured data display
- Bluetooth Plotter - For data visualization
- Multiple Bluetooth Apps - Combining monitor with other apps
Support
For additional help:
- Check the API Reference documentation
- Visit DIYables tutorials
- Arduino community forums