Android App that Sends a Message to Your Arduino

In this project I’m going to show an Android app that sends a message to your Arduino via bluetooth. And that message will be displayed in a Doted Matrix display.

Resources for this project:

Watch the video below

Parts Required




Source Code

Note: If you want to edit my app this is what you need to do. Download Send_Message.aia and upload it to MIT App Inventor. 


  • You need to remove the RX and TX cables when you’re uploading the sketch to your Arduino.
  • Sometimes people connect the TX from the bluetooth module to the TX of the Arduino… that’s wrong and it won’t work. Make sure you connect it properly, the TX into RX and the RX into the TX.
  • If the HC-05 Bluetooth Module asks for a password, It’s ’1234′.
  • Before Testing my android app, test if you’ve made all the connections correctly. How you can do that? Simply enter some messages (for example: “Random”) into your serial monitor and your DMD should display that message.

I hope you found this useful!

Do you have any questions? Leave a comment down below!

Related Content: Like ESP8266? Check out Home Automation Using ESP8266

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P.S. Click here to see how to use MIT App Inventor with Arduino


  1. Brit says

    just wanted to say your program works great.

    I would like to add a checkbox to be able to have an option to turn a buzzer on for 2 seconds when a text is sent, any ideas how I can accomplish this I am new to Mit and arduino. thank you for any help

    • Rui Santos says

      Hi Brit,
      MIT App Inventor comes already with a checkbox function.
      Under the menu called: “User Interface” search for “checkbox” and drag and drop into your app screen.

      Then go to the Blocks section and create an if condition.
      If that checkbox is ticked it also sends something else that the arduino will recognize and trigger the buzzer.
      I hope this helps,

  2. Shantanu Biswas says

    Hello Rui,
    Another Great upload!!!!!!
    But finding difficulty to download send_message.apk app,because the link provided by you is directing me to send_message.aia.
    So please give an appropriate link to download send_message.apk
    I shall be thankful to you.

    • Rui Santos says

      Yes Kerry,
      Feel free to add as much characters as you want.
      Just change the arduino code, instead of saving 100 characters change the size of the array to 1000 :)

  3. Shantanu Biswas says

    Can we use a long range bluetooth module like NRF24L01, so that we can send texts from a long distance.The link is provided below:

    • says

      Hi Shantanu,
      I think so. any bluetooth module that works with a simple serial communication at 9600 baud rate. Should work just fine with this project!

  4. Kerry Jackson says

    When I use more than 2 displays some of the characters from the phone are dropped. Any suggestions of why. Using 4 displays. Only 2 displays work…

    • says

      You might need to change some of the arduino code that is printing the string received from the android app.
      But before you change my arduino code. You should create a Serial.println() to see what your arduino is receiving from the smartphone and see if everything is working properly..

  5. Sagar says

    Hi Rui!

    Now i want to work on the sounds, i mean a buzzer for every new message.
    Can you please EMail me the schematic in Fritz format? Will help me a lot.


    • says

      Hi Sagar,
      Unfortunately I don’t have the fritizing schematics for this project anymore… at least I can find them on my computer.
      Have a nice day,

  6. Sagar says

    DMD working fine, bluetooth is also working fine, app is also getting connected to the bluetooth. We also followed your specified guidelines, but still we are facing problems in the form of the DMD not displaying the specified message from that app.
    Your assistance will be highly appreciated.
    Awaiting your reply.
    Thank you.

  7. Shantanu Biswas says

    Is it mandatory to use Arduino UNO?????
    Doesn’t it work with Arduino Duemilanove???
    Because we are using the latter i.e Duemilanove, and the Message is not being displayed in the DMD.
    Please Help!!!!

  8. Fernando says

    Descarque el archivo pero App Inventor no me permite importar el archivo me dice que no es compatible. A que se debe?. Gracias

  9. Jesjeet says

    Hi Rui,

    I would like to know since I am intending to use this same idea to create an android app on a different platform which will be android studio. Plus I would like to add the features like templates and make the displayed messages to be static and i need to increase the range of the Bluetooth. Will i still be able to use your codes with some editing or the codes wont work since the development platform is totally different.

    • says

      Hi Jesjeet,
      As you said the platform I’m using (MIT App Inventor) is totally different,
      so you can’t use my applications with Android studio.
      I might do some projects with Android Studio in the future, but right now I have plenty of other projects to finish.

  10. Steve Tripoli says

    Thanks for a great tutorial. I do have a question, the LED board is a little expensive do you think or can you do a tutorial using 8 of these,

    they are MAX7219 Dot matrix module MCU control Display module ?

  11. Steve Tripoli says

    Hello, both of the links for the Android phone app are the save, they both are .aia files. The one which says “Send_Message.apk” , after I unzip it is also “Send_Message.aia”
    Can you post the “Send_Message.apk” so I can run it on my phone?

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