This document provides instructions for using MIT App Inventor and a $5 Bluetooth module to wirelessly control an Arduino project from an Android device. It details what hardware and software is needed, including an Android device, Arduino, HC-05 Bluetooth module, MIT App Inventor account. It explains how to design the app interface in App Inventor, connect the Bluetooth module to the Arduino, and install the app on the Android device. Code examples are provided to transmit data between the app and Arduino over Bluetooth to control an LED.

1. Make It Talk!
Use MIT App Inventor and a $5 Bluetooth module to wirelessly control an
Arduino project from an Android device.

2. What you will need:
● Computer with Internet access
● Android smartphone or tablet (JellyBean or newer)
● Arduino
● HC-05 Bluetooth to UART Serial Transceiver (eBay or Amazon)
● Free account at MIT App Inventor website
https://ai2.appinventor.mit.edu

3. MIT App Inventor: Designer Window

4. MIT App Inventor: Blocks Window

5. Getting the App to your Android Device
● Install Google Goggles
● In Settings on device, allow ‘Unknown
Sources’ app installs under Security
● From App Inventor click:
o Build
o App (Provide QR code for .apk)
● Scan QR code with Google Goggles and
install
Ask me about the AI Companion app! Great for testing!
There is also an emulator that can be downloaded

6. #define pins and command codes
initialize the Bluetooth stream and declare
variables
Startup the Bluetooth connection and turn off
LED
Sit and listen for data to come in over the
Bluetooth serial stream
If we see a ‘1’ turn the LED on
If we see a ‘0’ turn the LED off
Arduino IDE

7. HC-05 modules don’t come from a single
vendor.
All HC-05s I’ve dealt with are 5V tolerant.
There is a chance though the not all are,
some may require 3.3V maximum!
Most Arduinos are 5V output on the GPIO
pins.
Except the newest Arduinos!
Arduino Zero does have 3.3V GPIO pins,
and most likely all future Arduinos will move
to 3.3V.
99% of the time, this circuit will work just fine
since all all HC-05s I’ve seen have 5V-3V
level shifter...
Default passcode:
1234

8. But just to be safe
you can add a voltage divider
Voltage divider is built using two
resistors.
We will place ours between the
Arduino TX pin (pin 11) and the
HC-05 RX pin.
4.7K-ohm
10K-ohm
Vout = Vin * [ R2 / (R1+R2) ] = 5V * (10K/14.7K) = 3.4V

9. Shortcut!
github.com/geekcowboy/AppInventor_Arduino_Bluetooth
Upload the .aia file into your App Inventor account by clicking on:
● Projects
● Import project (.aia) from my computer
Open the .ino file in the Arduino IDE, tweak as needed, and then upload to your Arduino
head on over to

10. Thank You!
● Luis Picarzo - App Inventor tutorial
o whatakuai.com/bluetooth-and-app-inventor/
● Mohannad Rawashdeh - HC-05 tutorial
o instructables.com/id/Arduino-AND-Bluetooth-HC-05-Connecting-easily