Controlling Raspberry Pi GPIO using Android App over Bluetooth

Raspberry Pi is very popular for IoT projects because of its seamless ability of wireless communication over internet. Raspberry Pi 3 has inbuilt Wi-Fi and Bluetooth, and Bluetooth is a very popular wireless communication Protocol. So today we are going to Control Raspberry Pi GPIO Pin through an Android app using Bluetooth.

Here we are using Raspberry 2 Pi Model B which don’t have inbuilt Bluetooth, so we are using a simple USB Bluetooth dongle. Apart from that we only need a resistor (220R) and a LED to demonstrate the GPIO controlling. Here we are using RFCOMM Bluetooth protocol for wireless communication.

Programming for Bluetooth in Python follows the socket programming model and communications between the Bluetooth devices is done through RFCOMM socket. RFCOMM (Radio Frequency Communication) is a Bluetooth Protocol which provided emulated RS-232 serial ports and also called as Serial Port Emulation. Bluetooth serial port profile is based on this protocol. RFCOMM is very popular in Bluetooth applications because of its wide support and publically available API. It is bound to L2CAP protocol.

We have also used Bluetooth module HC-06 in our previous project: Voice controlled LEDs using Raspberry Pi. Also check our previous Raspberry Pi Projects along with some good IoT Projects.

 

Installing Required Packages for Bluetooth Communication:

Before start, we need to install some softwares for setting up Bluetooth communication in Raspberry Pi. You should have a Raspbian Jessie installed memory card ready with Raspberry Pi. Check this article to install the Raspbian OS and getting started with Raspberry Pi. So now we first need to update the Raspbian using below commands:

sudo apt-get update
sudo apt-get upgrade

 

Then we need to install few Bluetooth related packages:

sudo apt-get install bluetooth blueman bluez

Then reboot the Raspberry Pi:

sudo reboot

BlueZ is a open source project and official Linux Bluetooth protocol stack. It supports all the core Bluetooth protocols and now become part of official Linux Kernel.

Blueman provides the Desktop interface to manage and control the Bluetooth devices.

 

Finally we need python Library for Bluetooth communication so that we can send and receive data through RFCOMM using Python language:

sudo apt-get install python-bluetooth

 

Also install the GPIO support libraries for Raspberry Pi:

sudo apt-get install python-rpi.gpio

 

Now we are done with installing required packages for Bluetooth communication in Raspberry Pi.

 

Pairing Devices with Raspberry Pi over Bluetooth:

Pairing Bluetooth Devices, like mobile phone, with Raspberry Pi is very easy. Here we have paired our Android Smart phone with Raspberry Pi. We have previously installed BlueZ in Pi, which provides a command line utility called “bluetoothctl” to manage our Bluetooth devices. But before that, connect your USB Bluetooth dongle with Raspberry Pi and check that whether it is detected or not, by using below command:

lsusb

 

Now open the bluetoothctl utility by below command:

sudo bluetoothctl

You can check all the commands of bluetoothctl utility by typing ‘help’. For now we need to enter below commands in given order:

[bluetooth]# power on
[bluetooth]# agent on
[bluetooth]# discoverable on
[bluetooth]# pairable on
[bluetooth]# scan on

After the last command “scan on”, you will see your Bluetooth device (Mobile phone) in the list. Make sure that your mobile has Bluetooth turned on and visible by nearby devices. Then copy the MAC address of you device and pair it by using given command:

pair <address of your phone>

Then you will be prompted for Passcode or Pin in your Terminal console then type passcode there and press enter. Then type the same passcode in your mobile phone when prompted and you are now successfully paired with Raspberry Pi. We have also explained this whole process in our Video given at the end.

 

As told earlier, you can also use Desktop interface to pair the Mobile phone. After installing Blueman, you will see a Bluetooth icon in right side of your Raspberry Pi desktop as shown below, using which you can easily do the pairing.

 

Circuit Diagram:

Circuit diagram is very simple, we just connected a LED to PIN 40 (GPIO 21) of Raspberry Pi with a resistor of 220 Ohm:

 

Controlling LED with Android App BlueTerm:

Now after paring the Mobile Phone, we need to install a Android App for communicating with Raspberry Pi using a Bluetooth Serial Adapter. As told earlier RFCOMM/SPP protocol emulates serial communication over Bluetooth, so we installed here BlueTerm App which supports this protocol.

You can also use any other Bluetooth Terminal App which supports communication via RFCOMM socket.

Now after downloading and installing the BlueTerm App, run the below given Python Program from the terminal and connect the paired raspberrypi device from the BlueTerm App at the same time.

 

After successful connection you will see connected:raspberrypi at the top right corner of the App as shown below:

                 

Now you can just enter ‘1’ or ‘0’ from the BlueTerm app to make the GPIO pin HIGH and LOW respectively, which in turns switch ON and OFF the LED connected to this pin. Press ‘q’ to exit the program. You can use Google Voice Typing Keyboard to control the GPIO using your Voice. Check the complete demo in the Video given at the end.

So this is how you can wirelessly control the GPIO Pin using an Android App over Bluetooth. Also check How to use Bluetooth with Arduino.

 

Programming Explanation:

Python Program for Controlling Raspberry Pi GPIO with Android App is very simple and self-explanatory. Only we need to learn little bit about the code related to Bluetooth RFCOMM communication. First we need to import the Bluetooth socket library which enables us to control Bluetooth with Python language; we have installed the library for the same in the previous section.

import Bluetooth

 

Below is the code responsible for Bluetooth communication:

server_socket=bluetooth.BluetoothSocket( bluetooth.RFCOMM )
 
port = 1
server_socket.bind(("",port))
server_socket.listen(1)
 
client_socket,address = server_socket.accept()
print "Accepted connection from ",address
while 1:
 
 data = client_socket.recv(1024)

Here we can understand them line by line:

server_socket=bluetooth.BluetoothSocket( bluetooth.RFCOMM ): Creating socket for Bluetooth RFCOMM communication.

server_socket.bind(("", port):- Server binds the script on host '' to port.

server_socket.listen(1): Server listens to accept one connection at a time.

client_socket, address = server_socket.accept(): Server accepts client’s connection request and assign the mac address to the variable address, client_socket is the client’s socket

data = client_socket.recv(1024):  Receive data through the client socket client_socket and assign it to the variable data. Maximum 1024 characters can be received at a time.

 

Finally after all the programming, close the client and server connection using below code:

client_socket.close()
server_socket.close()

 

All the other code is easy and self-explanatory. Check the full code below. Try to modify this project and you can use it to control many other things wirelessly, like using Relays you can control the home appliances or can also control a Robot car through android phone.

sudo apt-get install python-bluetooth

sudo apt-get install python-rpi.gpio