Yesterday I posted another item in a series of posts about using Bluetooth features in App Inventor. Bluetooth (together with low power wireless technologies such as Zigbee) are significant technologies that make “The Internet of Things” possible. These low power wireless technologies enable all kinds of devices to communicate with each other and with other devices such as Android phones and tablets.
Today, most Bluetooth devices run Bluetooth version 2.1 up through version 4.2, depending on the device. Bluetooth has undergone considerable enhancements and evolution over the years from providing a short range, lower speed serial data link suited for wireless earphones to providing high speed packet data communications over short distances while using very low power.
Bluetooth continues to evolve with Bluetooth version 5.
Bluetooth 5 adds more improvements including:
Up to 4x longer range
Faster data rates – on par with WiFi for some applications
However – and this is important, most Bluetooth version upgrades require new hardware, and this is true for Bluetooth 5. To use version 5 features you will need version 5 compatible hardware – which is not yet generally available on Android phones and tablets.
This tutorial shows how an App Inventor app can communicate with 2 (or more) Arduino boards and Bluetooth devices simultaneously. These instructions assume you are familiar with the code and hardware presented in Part 1 and Part 2 and “How to connect App Inventor apps to Arduino using Bluetooth“. This tutorial uses the same Arduino source code as in that tutorial.
A follow up tutorial will show how to simplify some of this code for supporting multiple Bluetooth devices.
Bluetooth is a short range, low power, limited speed wireless communications technology. The original Bluetooth technology provided a serial communications link between two paired devices (as compared to an individual data packet sent between up to n devices using the much newer Bluetooth LE – see here and here for information on Bluetooth LE).
Arduino is a microcontroller board for building hardware projects. You can write software for Arduino using a programming language similar to the C++ programming language.
The code used in these examples has been tested with some specific Bluetooth modules connected to Arduino. These include the JY-MCU (Amazon (Prime), Amazon (non-Prime) and also some HC-05 and HC-06 based Bluetooth modules.
Build two Arduino boards each with an appropriate Bluetooth module as described in the prior tutorial.
Compile and load the Arduino software in to each of the Arduino boards.
Test and confirm that your basic LED lights flash for the original, single Bluetooth connection case.
Then, with two working boards, continue to this tutorial.
User Interface View
The original app supported just one device, so there was just a single “Connect” and “Disconnect” button. This version demonstrates how to connect more than one Bluetooth device so we need separate buttons for each device. Similarly, we must add a second status and data sending item to the screen:
Before running this app, be sure to use Android | Settings | Bluetooth to “pair” your Bluetooth devices with Android.
Then, run the app and select Connect to Device 1. This displays a list of available Bluetooth devices in the vicinity. Select your specific Bluetooth device for the connection. Do this for both Bluetooth devices.
Once connected, you can send some simple commands to the Arduino board. Commands are very simple – a single number – to tell the Arduino to do something (this confirms that the Bluetooth link is working). If we enter a single digit 1 and then press Send Numeric 1, the Arduino board will send back 2 bytes of data which will then be displayed on the app screen. If we enter a single digit 4 and then press Send Numeric 1, a value of 4 is transmitted over Bluetooth to the Arduino board, which responds by flashing the externally connected LED.
Because the text box for data entry has its property set to NumbersOnly, a pop up numeric keypad displays when entering data, rather than the usual Android text keyboard.
Video Demonstration this App
I created a short video showing this app in operation. There are two versions of the video – one is standard 2D format and the other is in VR 3D format for viewing on Google Cardboard-like viewers used with smart phones to watch VR videos.