Bluetooth Connection for Arduinos

Often you want to establish a wireless connection to an Arduino. For example, you can remote control robots or transfer measurement data to a computer for further evaluation.

If you do not need large distances, bluetooth is usually the easiest and cheapest option. In this tutorial I explain how you can build a wireless connection between an Arduino and another Bluetooth-enabled device (tablet, mobile) with little effort.

Required parts:
1 x Arduino Uno (or compatible)
1 x HM 10 BLE Bluetooth - module 
4 x jumper cable male - female 
1 x Bluetooth enabled device with Bluetooth software  

The HM 10 BLE Bluetooth Module

The HM-10 is a readily available Bluetooth 4.0 module. This module is used for establishing wireless data communication. The module is designed by using the Texas Instruments CC2540 or CC2541 Bluetooth low energy (BLE) System on Chip (SoC). The module design and firmware originated from the Jinan Huamao Technology Company. As the name suggests, BLE focuses on low energy consumption. Low energy focus comes with some sacrifices particularly around data transfer rates and the range of operation.

Wiring Diagram for HM 10

The below circuit diagram gives a basic idea how a HM-10 can be interfaced with Arduino UNO. The communication between the Arduino and the HM10 is done via the UART interface. UART stands for Universal Asynchronous Receiver/Transmitter. It is a hardware device used for serial communication between two devices. Connecting two UART devices together is simple and straightforward: Only two pins are required on each device. One pin is for transmitting data (TX pin) and the other is for receiving data (RX pin). We can only connect two UART devices together.

Arduino           HM-10
7 (RX)             TX
8 (TX)             RX
5V                 VCC
GND                GND 

Program for Bluetooth - Connection

As always, the Arduino makes it easy for us to use the built-in UART hardware by using the serial object. The serial object has the necessary functions for an easy use of the Arduino’s UART interface. To communicate via the UART interface, we need to configure it first. The easiest way to configure the Arduino’s UART is by using the function Serial.begin(speed). The speed parameter is the baud rate that we want the UART to run.

To check if there is data waiting to be read in the UART (or serial) buffer, we will use the function Serial.available(). Serial.available() returns the number of bytes waiting in the buffer.

// Bluetooth Connection to Arduino
// Attention: The HM 10 uses Bluetooth LE (Low Energy), makes sure that the program
// you use for communicating also supports BT LE (I use the Serial Bluetoot Terminal)
// With this test software you can send text messages to your arduino and vice versa.
// Stefan Hager (2022)
#include <SoftwareSerial.h>

// use pin 7 as RX and pin 8 as TX

SoftwareSerial bluetooth(7,8);

void setup()
  Serial.println("Bluetooth test running ...");

void loop()
  // wait for incoming data and print message to serial monitor
    String msg = readStringFromBluetooth();
  // wait for the user to type a message into the serial monitor and 
  // send it to the connected device

String readStringFromBluetooth()
  String message = "";

  while (bluetooth.available())
    // read one character from serial connection and add to message    
    char in_char =;
    message = message + in_char;
  return message;

Running the Program

In order to be able to test the program, you need a bluetooth-capable device with a display, for example a cell phone or a tablet. On the device you need a software that can send data to the bluetooth interface of the device and display received data. You can use for example the "Serial Bluetooth Terminal" as software.

The test program displays all received data into the serial monitor window, any user input into the serial monitor are sent to the connected device.