For another device like a smartphone to use any of the Bluetooth “services” which the Calliope mini has, it must first be paired with the Calliope mini. Once paired, the other device may connect to the Calliope mini and exchange data relating to many of the Calliope mini’s features.
The Bluetooth UART service allows another device such as a smartphone to exchange any data it wants to with the Calliope mini, in small chunks which are intended to be joined together. UART stands for Universal Asynchronous Receiver Transmitter and is one way in which serial data communications can be performed, usually between two devices connected by a physical, wired connection. The Bluetooth UART service emulates the behaviour of a physical UART system and allows the exchange of a maximum of 20 bytes of data at a time in either direction.
When this service is used, the Calliope mini sets up a 60 byte buffer and data it receives will be accumulated in the buffer until it is full. When using the UART service from your Calliope mini code, you can indicate a special character which will be used to mean that the entire message in at most three chunks has now been sent by the other, connected device, at which point the Calliope mini will release the entire contents of its buffer to any code trying to read it. In other words this special character, known as a ‘delimiter’ is used by the device connected to the Calliope mini to mean “I’ve sent my whole message, you can now use it”.
You could use the UART service for many things. It doesn’t care what you put in messages which makes it very flexible. You could create a guessing game, with questions and answers passing between Calliope mini and a smartphone or you could connect a camera to the Calliope mini and transmit image data obtained from the edge connector, in chunks over Bluetooth to a smartphone. There are a great many possibilities.
To use the Bluetooth UART service from another device you’ll need additional Calliope mini code which reads and uses data from the UART buffer and / or writes data to the buffer for transmission over Bluetooth to another device.
bluetooth.startUartService();The following code shows the Bluetooth UART service being started:
bluetooth.startUartService();For more advanced information on the Calliope mini Bluetooth UART service including information on using a smartphone, see the Lancaster University Calliope mini runtime technical documentation
About Bluetooth, Calliope mini Bluetooth profile overview , Calliope mini Bluetooth profile reference, Bluetooth on Calliope mini resources, Bluetooth SIG
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