How to control arduino board using an android phone and a bluetooth module

Picture of How to control arduino board using an android phone and a bluetooth module
In this tutorial you'll learn how to use a bluetooth module and MIT's app inventor to create a wireless serial link between an android phone and an arduino board.

Here is a short video showing an example app I created. I'll describe how to do the wiring, write an arduino sketch that can accept basic commands and send them and how to write the app itself. I asume you're already familiar with some of the basics, you made a few arduino projects and are familiar with the arduino IDE. If you have attempted serial communication with the arduino board everything should be fully comprehensible. If you have any problems or questions feel free to ask them in the comments section.

...and here is an example of receiving the data from the arduino board on the mobile. The temperature sensor connected to the arduino board is a ds18b20 sensor. Just to show how awesome app inventor is I added text to speech functionality - the app says the temperature every 15 seconds. The arduino code and the app is described in more detail in steps 4,5 and 6.
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Step 1: Wiring & part list

Picture of Wiring & part list
The circuit is as simple as it gets so you probably already have most of them.

You will need:
- arduino board
- bluetooth serial module (I used a btm222 module on a breakout board with an inbuilt regulator )
- an LED
- resistor (100ohm)
- wires
- breadboard

The only problematic part here is the bluetooth module. There are different modules all over the internet so be sure you check the pinout in the datasheet of the one you get as it can differ.

Also notice that there are two general classes of bluetooth modules:
Class 1 has range of about 100 meter (300 feet)
Class 2 has range of about 10meter (30 feet)
In case you're wondering they are entirely compatible and you can only get 100 meter range if both of the devices (ie the mobile and the serial module) are class one. If one of it is class 1 the maximum range is lower.

The bluetooth serial module I got has the following pins from left to right (ground, RX, TX, not connected, VCC). Obviously ground and VCC goes respectively to ground and +5V pin on the arduino board. Since we will be receiveing the data through the module and then in turn sending it to the arduino board we only need to use the TX pin on the module. Run a wire from that pin to the RX pin on the arduino board. The Led is controlled through PIN 2 on the arduino.

Step 2: Arduino code

Below is an arduino code I used. Feel free to modify it.

The important aspect here is the baud rate - make sure it matches the baud rate of your module - check the datasheet or use AT commands to do it.

const int ledPin = 2;      // the pin that the LED is attached to
  byte serialA;
void setup()
  // initialize the serial communication:
  Serial.begin(19200); //baud rate - make sure it matches that of the module you got:
  // initialize the ledPin as an output:
  pinMode(ledPin, OUTPUT);

void loop() {

if (Serial.available() > 0) {serialA = Serial.read();Serial.println(serialA);}

      switch (serialA) {
    case 1:
      digitalWrite(ledPin, HIGH);
    case 2:
      digitalWrite(ledPin, LOW);
    case 3:digitalWrite(ledPin, HIGH);
      digitalWrite(ledPin, LOW);



Step 3: The app itself & App inventor

Picture of The app itself & App inventor
If all you want is to get the app and see it running then download the app then upload it to your phone.
Download at -> https://drive.google.com/folderview?id=0B_PfPoEotOF8N2JwT3RSX011SjQ&usp=sharing

Your phone has to be set to allow apps from outside the android market/google play to be able to download them - so check the settings on your mobile.

Now if you want to modify the app go to >>
to find out how to prepare your computer and install App inventor software. Once you have it running I suggest you do at least one or two of their basic tutorials.

Below is the source of the app that I used. You can upload it to the app inventor and then upload to your phone or modify it.

Step 4: Receiving data from arduino

This step presents an example on how to receive data from the arduino board.

I decided to make something useful so I chose a ds18b20 temperature sensor. The arduino board communicates with the sensor using 1 wire interface, calculates the temperature with the help of OneWire library for arduino and sends the readings through the bluetooth module every 500 ms.

The app checks every 500 ms if there is any data available from the serial port. If data is present it is read and displayed on the screen. Additionally, there is an option to activate text to speech function and make the app say the temperature readings every 15 seconds.

Step 5: Remote sensor - arduino code

The arduino code
Mind you that you need a OneWire library - you can find a link to it here:

arduino code >>>>>>>

#include <OneWire.h>
int DS18S20_Pin = 2; //DS18S20 Signal pin on digital 2

//Temperature chip i/o
OneWire ds(DS18S20_Pin); // on digital pin 2

void setup()
  // initialize the serial communication:
  // initialize the ledPin as an output:


void loop() {

   float temperature = getTemp();
Serial.println(temperature); delay (500);


float getTemp(){
//returns the temperature from one DS18S20 in DEG Celsius

byte data[12];
byte addr[8];

if ( !ds.search(addr)) {
//no more sensors on chain, reset search
return -100;

if ( OneWire::crc8( addr, 7) != addr[7]) {
Serial.println("CRC is not valid!");
return -1000;

if ( addr[0] != 0x10 && addr[0] != 0x28) {
Serial.print("Device is not recognized");
return -1000;

ds.write(0x44,1); // start conversion, with parasite power on at the end

byte present = ds.reset();
ds.write(0xBE); // Read Scratchpad

for (int i = 0; i < 9; i++) {
data[i] = ds.read();


byte MSB = data[1];
byte LSB = data[0];

float tempRead = ((MSB << 8) | LSB);
float TemperatureSum = tempRead / 16;

return TemperatureSum;}

Step 6: Receiving data - the application side

Here you can find links to the app that receives temperature reading. There is also a source code that can be uploaded into MIT's app inventor (when you're in 'my projects' click the button 'More Actions' - you have an option 'Upload Source')

feel free to modify it ;-)

The application >>

The source file >>

I'll try to add something more descriptive soon, but here are some tips you might find useful if you're trying to create your own app: Make sure you understand the terms 'delimiter byte', know how to set it from MIT's app inventor and that it is a byte so be careful what data types you use. Also it seems that there is no serial timeout function implemented in the app inventor so sending data more often than receiving it can cause the app to crash (probably because there isn't anything to flush the buffer)
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If anyone is still following this topic and they are still looking for a way to convert from "Classic" App Inventor (.blk) to AI2 (.aia) then go to this link http://appinventor.mit.edu/explore/classic.html

They talk about the demise of AI classic but part way down the page they give a link to a converter. Click on the link and follow instructions. Make sure you point it to the .zip file not the extracted files and presto... works like a charm.

HimanshuP21 month ago

Android App:
BlueUino: Bluetooth Remote for Arduino, Control your Arduino Over Voice as well as Buttons

If you want to make app like this as per you requirements please Email me : micky.patel41@gmail.com.
Visit web site for more info : blueuino.blogspot.com.

SadanandT2 months ago

find the code given in below link and troubleshooting techniques and circuit diagram


sirinehas2 months ago

this is exactly what i need but i have to do the android code with Android studio can you help me pleaaaaaaaaaaaaaase :) :)

AhmedDaher9903 months ago

Hello... may you please help me in my project, What the requirement i need it to done my project. I want to control my room lights by using android phone but actually im confused how i can do it. What kind of tools and devices that help me to complete my project by using arduino. Thank you

JasonL154 months ago

Can somebody upload a .aia file for the app inventor? I cannot figure out how to import any of the files from that google drive into my app inventor.

Justin_T44 months ago

Hey, I was pretty close to getting everything working. Just one question. This is the Bluetooth module I have http://www.tinyosshop.com/index.php?route=product/product&product_id=705 will this work? it connects to the device but wont connect to your app or any other app emulators.

thanks for the explanation , I will try soon . if I have not could please help me. thank you

javierrios734 months ago

Hola, como termina el diseño de la aplicación en App inventor porque en la imagen en la parte baja no se alcanza a ver?


app program.jpg

Hello ,i tried this tutorial using the blutoothF2M03GLA BUT IT IS NIT Working , can i get ur help plz? realy feel lost !

hey @kerimil nice tutorial, I am having an issue sending data to the arduino with appinventor. The data is being sent but the HC-06 seems to be misinterpreting the sent data. I think it has something to do with the DelimiterByte value that is being used in appinventor 2. Right now it defaults to "0". I attached a logic analyzer to see if I could identify the issue and I am getting framing errors. I am not sure what to think, any advice on the DelimiterByte? does that deliminate the byes or the sentence?

Hi kerimil. Great article. i wanna ask your advice and opinion regarding my project. i'm working on a project (final year project in university) where i try to make a tracker that can be controlled by android application. I'm trying to make the application can

1) set the maximum distance between the tracker device and the phone

2) trace the distance between the device and the phone,

3) phone will produce a sound when the device reach the maximum distance

so, what's your opinion? how can i make this using arduino? which kit? I really dont know anything about arduino. thanks :-)

automagdon7 months ago

Hi Kerimil;

Great article, thanks for taking the time to post it. I got it to work but know I want to dig in and understand your code. I'm not at all familiar with app inventor, but it looks cool, a lot friendlier than Eclipse!

How do I import your files into App Inventor, I know how to import the aia files but can't find anything on importing the .scm and .blk files you supplied.

Happy New Year!!


flagtrax7 months ago
@kerimil Thank you for the response regarding the issue of App inventor classic vs. App inventor 2.I worked around that. But there is however a glitch in the App Inventor compiler regarding the block to "evaluate and ignor results". The reply I got from the forum was that "MIT was aware of the problem and would correct it in the next release." I used a block that was insignificant to the end result as a substitute just to test and it worked. I'm just posting this to alert all newbies like myself to be aware of the issue. Thanks to all who share their knowledge.
archy5877 months ago

Im doin the same project but building the app from the BluetoothChat example in Eclipse. I can get messages back and forth but I dont know how to get the 'delimiter byte' correct. my formatted lines sent from arduino are broken up into different strings in android, so I cant figure out how to parse them properly. I would like to see how your app strings all the incomming data together. does appInventor produce java files you could add to google drive so i could see how its working?


kerimil (author)  archy5877 months ago

Well then just write arduino code that sends everything as one string and then your android app divides the strings into substrings that contain data you want. It's actually more of a problem of operation on string than arduino or android problem.

archy587 kerimil7 months ago

yea, i wanted to see how your app is dividing the strings into substring. Im not very good with java. i did come up with a solution that works only if the arduino outputs a string of an exact length. I guess thats a first step...now just gotta clean it up a bit. anyway....thanks for the post and the reply!

JohnN39 months ago

kerimil, Thank you for sharing your experiences and knowledge. After retiring from a 30 year career in electronics the arduino platform has excited me again. I've build many discrete circuits, but building module to module is a whole new experience. I enjoyed this exercise however I am confused about a couple things (probably due to my inexperience). I've completed the led part and the on/off buttons work great. The voice command for on and off worked but blink didn't. I have just started playing with app inventor and wanted to load your build as you suggested in your narrative, to see what was happening but when I got to the page that was linked to I found a bunch of files and didn't know which one I was to download. If you could help me choose the correct one, you'd make an old man happy, then do I manually rebuild in the app inventor, or is there a way to upload it? Thanks again!

ed.darby JohnN39 months ago

Hi JohnN3

I too had the same problem, I did some digging and it appears that the original app was built in App Inventor Version 1 which isn't compatible with the version 2 that is available now.

If you download the zip file listed in the article "bluetoothforarduino_app" from https://drive.google.com/folderview?id=0B_PfPoEotO... - you can go to - http://appinventor.mit.edu/explore/classic.html and import the zip file into "Classic" app inventor by going to "My Projects" then "More Actions" then "upload source" - The source being the zip file you d/lded above

Hope this helps :)


kerimil (author)  ed.darby7 months ago

That's right. The thing is that I wrote it before app inventor 2 was released. I need to get some spare time to rewrite it in it as roughly 70% of messages concern this problem. Hopefully will have some time around christmas.

JohnN3 ed.darby8 months ago

Thanks ed, I'll see if I can move ahead with your info thanks for sharing!

sandeep.laik8 months ago

Very useful .. faced a little challenge since MIT has come up with AI2 and the code can't be converted to eclipse or Android Studio but was worth the effort.

nero7771 year ago

Thanks , this post was very useful for me :) I managed to send data to the LCD screen by developing an app using your source code thanks alot.

I just have one question , now I'm trying to receive the data from the arduino and display it in a label so for example I want to print hello from this command in arduino Serial.print("Hello"); in a label . But the receive text function in the MIT software only sets it as bits not characters so I'm not able to receive it .

here is my work

I would be gratefull if you can hep me with this

Screenshot 2014-02-18 17.14.36.png
ShubhamM2 nero7778 months ago

brah!! help me through my project .My arduino UNO is responding to my app invented on mit2. i have used UTF-8 and delimiter byte 0.

kerimil (author)  nero7771 year ago

You have to specify number of bytes to receive in bluetoothclient.receivetext

Put there 0 (zero) and it will work just fine. Just remember to send a message with a delimiter byte.

Appinventor has help dialogs built in. If you keep you mouse pointer on any block or even part of it, a message will pop up saying what it does and how to use it. Try this out with the bluetoothclient.receivetext block and number of bytes ;-) you'll see why

ShubhamM2 kerimil8 months ago

Other apps from play store are working right (rx led is not blinking with this apps(ardudroid)) but my arduino is not responding to my app and rx led still not glowing

ShubhamM2 kerimil8 months ago

Hey i have invented an app on mit2. while using, the app is showing connections and is connecting to hc-05(i'm using) but while sending data over the bluetooth arduino is not responding. This my minor project . I have to submit it by Nov- 22 .plz someone help me.

ShubhamM2 kerimil8 months ago

Hey i have invented an app on mit2. while using, the app is showing connections and is connecting to hc-05(i'm using) but while sending data over the bluetooth arduino is not responding. This my minor project . I have to submit it by Nov- 22 .plz someone help me.

ShubhamM28 months ago

which file is useful from that G-Drive


The files you are sharing on Google Drive are all apk files. App inventor 2 only runs aia. I am hoping you can upload the aia file to Google Drive so I can view the program in app inventor.

Thank You

magorwilly8 months ago


I love this app. I would like to do some adjustments but the app inventor 2 doesnt allowe me to import zip only aia. Any chance you could send me a link to aia rather than zip. Please

jaydippatel8 months ago


jaydippatel8 months ago


_Hokusai8 months ago


flagtrax8 months ago
Thanks again ed for the steering :) interestingly, I was able to edit the app in the app inventor classic, download it and it worked (WOOT WOOT!)
How ever when I rewrote it using app inventor 2, I could edit it fine, it ran well using the app companion linked to my phone, but when I downloaded it, it crashed at the point where the bluetooth device is selected. It simply returns to the screen it was launched from. I'm wondering if anyone else has had issues like this with app inventor?
It also seems you can only download to your pc and not directly to the phone when using app inventor 2, unless I'm missing something.
CarloDoylo8 months ago

Hi, my name is Carla, from Barcelona. I'm studying Gamification and I need information about an app that let me control the arduino, and if its possible making a "menu" with the same app with six simply buttons.

I need to control something like this with the arduino (6 variables, 1. off the music of the piano (lights still work), off the lights of the piano (sound still work), on the lights (sound does not work), on the sound (light does not work), off all the system and on all the system at the same time.


TimothyB29 months ago

can you control a relay insted of a led?

JohnN3 TimothyB28 months ago

Yes, but be careful how you drive the relay, keeping in mind the load considerations on the arduino board you are using. There are many opto-isolated relay modules out there fairly inexpensive you can use safely. (I've found many on EBAY). The ones I have sort of work in reverse, with VCC being active and the input (control) lead being active low, meaning your digital write would be low to activate the relay. In this way VCC can be external to your arduino board, and the I/O pin is simply providing a low (Ground path) for the opto-isolator. To me this is the safest way to drive the relay. If you drive it direct you could exceed the current limits of the arduino I/O.

zs28 months ago

i have try this project using hc-06 but i cant get any data..i can connected to bluetooth but no data has been send to my android..and here my android block..can anybody here help me??

jkurarin11 months ago

can you post the App Inventor blocks for the Text-to-Speech function? pls pls pls :)

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