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Espruino is a JavaScript interpreter for low-power Microcontrollers. This site is both a support community for Espruino and a place to share what you are working on.
@Gordon
It's well worth reading this to get a better idea about BLE: http://www.espruino.com/About+Bluetooth+LE
You can use advertising to send the temperature, and small amounts of text (a few characters). This does basically what you want - including pushing data over MQTT on a Pi: http://www.espruino.com/Puck.js+Node-RED
Otherwise you need a connection. You can keep the Pi permanently connected to a Puck via the UART, but it's not ideal (the most connections a Pi can have open is something like 6).
You could create a service on the Pi with
bleat(or similar) and could then connect from the Puck to the Pi when you had data to send.Or the Puck could advertise if it had data ready, and then the Pi could connect to the Puck and request information via UART.
So there are loads of methods - but Advertising is by far the easiest most power efficient one :)