Arduino UNO R4 - DIYables Bluetooth App Temperature
Overview
The Bluetooth Temperature example provides a visual temperature gauge through the DIYables Bluetooth STEM app. Designed for Arduino UNO R4 WiFi using BLE (Bluetooth Low Energy) to display temperature readings with a configurable range and unit on your smartphone. Perfect for temperature monitoring, weather stations, HVAC projects, and environmental sensing.
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
- Visual Gauge: Beautiful temperature gauge display on smartphone
- Configurable Range: Set minimum and maximum temperature values
- Custom Unit: Display °C, °F, or any custom unit
- Real-Time Updates: Push temperature changes at configurable intervals
- On-Demand Request: App can request current temperature
- Works on Android & iOS: BLE is supported on both platforms
- No Pairing Required: BLE auto-connects without manual pairing
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 .
Buy Note: Many DS18B20 sensors available in the market are unreliable. We strongly recommend buying the sensor from the DIYables brand using the link provided above. We tested it, and it worked reliably.
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_Temperature example, or copy the above code and paste it to the editor of Arduino IDE
/*
* DIYables Bluetooth Library - Bluetooth Temperature Example
* Works with DIYables Bluetooth STEM app on Android and iOS
*
* This example demonstrates the Bluetooth Temperature feature:
* - Display temperature sensor readings
* - Configurable temperature range and unit
* - Real-time temperature updates
*
* 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
*
* Optional: Temperature sensor (DHT22, DS18B20, or analog thermistor)
*
* 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 temperature
*
* Tutorial: https://diyables.io/bluetooth-app
* Author: DIYables
*/
#include <DIYables_BluetoothServer.h>
#include <DIYables_BluetoothTemperature.h>
#include <platforms/DIYables_ArduinoBLE.h>
// BLE Configuration
const char* DEVICE_NAME = "Arduino_Temp";
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 Temperature app instance (min=-10°C, max=50°C, unit="°C")
DIYables_BluetoothTemperature bluetoothTemperature(-10.0, 50.0, "°C");
// Variables for temperature simulation
float currentTemperature = 25.0;
unsigned long lastTempUpdate = 0;
const unsigned long TEMP_UPDATE_INTERVAL = 2000; // Update every 2 seconds
// Simulated temperature sensor reading
float readTemperature() {
// TODO: Replace with actual sensor reading
// Examples:
// - DHT22: dht.readTemperature()
// - DS18B20: sensors.getTempCByIndex(0)
// - Analog thermistor: analogToTemperature(analogRead(A0))
// Simulate temperature changes
static float offset = 0;
offset += random(-10, 11) / 10.0; // Random walk
if (offset > 5.0) offset = 5.0;
if (offset < -5.0) offset = -5.0;
return 25.0 + offset; // Base temperature 25°C with variation
}
void setup() {
Serial.begin(9600);
while (!Serial);
Serial.println("DIYables Bluetooth - Temperature Example");
// TODO: Initialize your temperature sensor here
// Examples:
// dht.begin();
// sensors.begin();
// Initialize Bluetooth server with platform-specific implementation
bluetoothServer.begin();
// Add temperature app to server
bluetoothServer.addApp(&bluetoothTemperature);
// Set up connection event callbacks
bluetoothServer.setOnConnected([]() {
Serial.println("Bluetooth connected!");
// Send initial temperature reading
float temp = readTemperature();
bluetoothTemperature.send(temp);
Serial.print("Initial temperature sent: ");
Serial.print(temp);
Serial.println("°C");
});
bluetoothServer.setOnDisconnected([]() {
Serial.println("Bluetooth disconnected!");
});
// Optional: Handle requests for temperature value
bluetoothTemperature.onTemperatureRequest([]() {
float temp = readTemperature();
bluetoothTemperature.send(temp);
Serial.print("Temperature requested - Sent: ");
Serial.print(temp);
Serial.println("°C");
});
// You can change temperature configuration at runtime:
// bluetoothTemperature.setRange(-40.0, 125.0); // Wide range for industrial sensors
// bluetoothTemperature.setUnit("°F"); // Change to Fahrenheit
Serial.println("Waiting for Bluetooth connection...");
}
void loop() {
// Handle Bluetooth server communications
bluetoothServer.loop();
// Send temperature updates periodically (only when connected)
if (bluetooth.isConnected() && millis() - lastTempUpdate >= TEMP_UPDATE_INTERVAL) {
lastTempUpdate = millis();
// Read temperature from sensor
currentTemperature = readTemperature();
// Send to Bluetooth app
bluetoothTemperature.send(currentTemperature);
// Print to Serial Monitor
Serial.print("Temperature: ");
Serial.print(currentTemperature);
Serial.println("°C");
}
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 - Temperature 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_Temp" in the scan results to connect.
- Once connected, the app automatically goes back to the home screen. Select the Temperature 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 a temperature gauge displaying the current reading with the configured range and unit
Now look back at the Serial Monitor on Arduino IDE. You will see:
COM6
Bluetooth connected!
Temperature: 24.50 °C
Temperature: 24.80 °C
Temperature: 25.10 °C
Autoscroll
Clear output
9600 baud
Newline
Creative Customization - Adapt the Code to Your Project
Configure Temperature Range and Unit
// Celsius: -10 to 50
DIYables_BluetoothTemperature bluetoothTemp(bluetoothServer, -10.0, 50.0, "°C");
// Fahrenheit: 0 to 120
DIYables_BluetoothTemperature bluetoothTemp(bluetoothServer, 0.0, 120.0, "°F");
// Custom range for industrial use
DIYables_BluetoothTemperature bluetoothTemp(bluetoothServer, -40.0, 200.0, "°C");
Send Temperature Updates
// Send temperature value to the app
bluetoothTemp.send(25.5);
// Read from a real sensor and send
float temp = readTemperatureSensor();
bluetoothTemp.send(temp);
Handle Temperature Requests
bluetoothTemp.onTemperatureRequest([]() {
float temp = readTemperatureSensor();
bluetoothTemp.send(temp);
Serial.print("Requested: ");
Serial.println(temp);
});
Programming Examples
DS18B20 Temperature Sensor
#include <OneWire.h>
#include <DallasTemperature.h>
OneWire oneWire(2);
DallasTemperature sensors(&oneWire);
DIYables_BluetoothTemperature bluetoothTemp(bluetoothServer, -10.0, 50.0, "°C");
void setup() {
sensors.begin();
bluetoothTemp.onTemperatureRequest([]() {
sensors.requestTemperatures();
float temp = sensors.getTempCByIndex(0);
bluetoothTemp.send(temp);
});
}
void loop() {
bluetoothServer.loop();
static unsigned long lastTime = 0;
if (millis() - lastTime >= 2000) {
lastTime = millis();
sensors.requestTemperatures();
float temp = sensors.getTempCByIndex(0);
bluetoothTemp.send(temp);
}
}
DHT22 Sensor with Fahrenheit
#include <DHT.h>
DHT dht(2, DHT22);
DIYables_BluetoothTemperature bluetoothTemp(bluetoothServer, 0.0, 120.0, "°F");
void setup() {
dht.begin();
bluetoothTemp.onTemperatureRequest([]() {
float temp = dht.readTemperature(true); // Fahrenheit
if (!isnan(temp)) {
bluetoothTemp.send(temp);
}
});
}
void loop() {
bluetoothServer.loop();
static unsigned long lastTime = 0;
if (millis() - lastTime >= 2000) {
lastTime = millis();
float temp = dht.readTemperature(true);
if (!isnan(temp)) {
bluetoothTemp.send(temp);
}
}
}
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. Temperature not updating
- Check that send() is being called in the loop
- Verify the update interval timing
- Ensure bluetoothServer.loop() is called
3. Temperature shows wrong range
- Check the min/max values in the constructor
- Make sure the unit string is correct
- Temperature value must be within the configured range
4. Sensor reading is NaN
- Verify sensor wiring connections
- Check sensor power supply
- Add isnan() check before sending
5. 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
- Room temperature monitor
- Greenhouse climate controller
- Refrigerator/freezer thermometer
- Weather station display
- Aquarium temperature monitor
Next Steps
After mastering the Bluetooth Temperature example, try:
- Bluetooth Analog Gauge - For general-purpose gauge display
- Bluetooth Plotter - For temperature logging over time
- Bluetooth Table - For multi-sensor display
- Multiple Bluetooth Apps - Combining temperature with other apps
Support
For additional help:
- Check the API Reference documentation
- Visit DIYables tutorials
- Arduino community forums