Android App that Sends a Message to Your Arduino

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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!

Thanks for reading. If you like this post probably you might like my next ones, so please support me by subscribing my blog and my Facebook Page.

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


  • ian

    Reply Reply February 18, 2014

    it took a series of adapter..

    • Rui Santos

      Reply Reply February 18, 2014

      Hi ian,
      What exactly you mean by that?

  • ian

    Reply Reply March 21, 2014

    whether it can function in Anroid 4.2?

  • ian

    Reply Reply March 21, 2014

    If I use the bluetooth hc-06 does not work? whether to use hc-05?

  • Brit

    Reply Reply April 20, 2014

    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

      Reply Reply April 25, 2014

      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,

  • Shantanu Biswas

    Reply Reply April 21, 2014

    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.

  • Kerry Jackson

    Reply Reply May 2, 2014

    How can I modify to enter a message of 1000 characters?

    • Rui Santos

      Reply Reply May 3, 2014

      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 :)

  • Shantanu Biswas

    Reply Reply May 12, 2014

    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:

    • Rui Santos

      Reply Reply May 17, 2014

      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!

  • Kerry Jackson

    Reply Reply May 27, 2014

    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…

    • Rui Santos

      Reply Reply June 8, 2014

      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..

  • Sagar

    Reply Reply June 21, 2014

    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.


    • Rui Santos

      Reply Reply June 24, 2014

      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,

  • Sagar

    Reply Reply July 21, 2014

    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.

    • Rui Santos

      Reply Reply July 21, 2014

      Are you using the same DMD as me?
      The DMD doesn’t display any message at all?
      is your bleutooth module working properly?
      By default most bluetooth modules are set a 9600 baud rate such as the arduino to establish a serial communication.
      If you bluetooth module is set at a different baud rate it won’t work properly and it won’t receive the message

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