This tutorial covers basic App Inventor Bluetooth communications code. Subsequent tutorials will add additional features. To implement and test this sample code, you need access to two Android devices – one to act as a Bluetooth “server” and the other to act as a “Bluetooth” client.
I tested this code using an old LG smart phone running Android 2.2 and a new Nexus 5 running Android 5.0.1. I also tested this code using the Nexus 5 paired with a Nexus 7 tablet.
This tutorial is lengthy – it introduces Bluetooth communications, then presents the user interface and blocks code for both the server and client programs, and then discusses how to set up the Bluetooth Communications link using “pairing”.
Downloadable App Inventor source code for the client and server is at the end of this post.
This is the first of several posts on Bluetooth. This first post covers basic connections and the sending and receiving of text between two Bluetooth devices. The two halves of the link – client and server – are kept in separate apps to keep this simple, however, it is possible for a single app to act as both a client and a server. A subsequent post will show how to send other types of data, such as numbers, and introduce additional features for using Bluetooth communications.
Introduction to Bluetooth
Bluetooth is the communications technology with a funny name. Bluetooth is actually named for a long ago Danish king who worked to unite groups of people, which is similar to Bluetooth’s goal of interconnecting different devices. The King’s real name was “Harald” but he had a nickname that translates as “Bluetooth” – no one knows for sure why he had this nickname but one thought is he had one dark tooth that may have appeared black or blue. And that is certainly an obscure way to choose a name for new technologies!
Bluetooth establishes a very low power, short range (up to 10 meters) communications link between two devices. Bluetooth uses the same frequency band (2.4 Ghz) as Wi-Fi, but uses different technology. Both Bluetooth and Wi-Fi use forms of spread spectrum radio links that result in signals moving around within a wide band in ways that enable sharing of the spectrum by multiple devices. But the two technologies serve different purposes, are not identical, and cannot communicate with one another.
Bluetooth applications include common wireless headsets for wired and cellular phones, and in-ear cordless adapters for phones. Bluetooth is also used by cordless headphones and to exchange address cards between devices, and for industrial applications where sensors collect and send data into a network.
There are two forms of Bluetooth – classic Bluetooth, which we use in the sample applications, and a newer version known as Bluetooth low energy, Bluetooth BLE, Bluetooth LE or Bluetooth Smart – all referring to the same new technology. The newest Android devices running Android 4.3 or newer, usually support the newest Bluetooth Smart technology. Regardless, we use classic Bluetooth which is backwards compatible to older phones, and is the technology supported by App Inventor.
Setting up a Bluetooth devices involves “pairing” the two devices and establishing a connection. This will be covered later in this tutorial.
 Actually there is another communications technology with a funny name called TWAIN, which is an acronym for “Technology without and interesting name” (really!)
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