Increased default power to 6, added UART write block

docs/reference/bluetooth/uart-write.md

@@ -0,0 +1,52 @@
+# UART Write 
+
+### ~hint
+![](/static/bluetooth/Bluetooth_SIG.png)
+
+For another device like a smartphone to use any of the Bluetooth "services" which the micro:bit has, it must first connect to the micro:bit.
+
+### ~
+
+The [Bluetooth UART service](start-uart-service.md) allows another device such as a smartphone to exchange any data it wants to with the micro:bit, in small chunks. 
+
+With the Bluetooth UART service running, this block allows a micro:bit to send data to a Bluetooth connected device.
+
+```sig
+bluetooth.uartWrite("");
+```
+
+### Example: Starting the Bluetooth UART service and then sending "HELLO" whenever button A is pressed and another device has connected over Bluetooth
+
+```blocks
+let connected = 0;
+bluetooth.onBluetoothConnected(() => {
+    basic.showString("C");
+    connected = 1;
+});
+bluetooth.onBluetoothDisconnected(() => {
+    basic.showString("D");
+    connected = 0;
+});
+bluetooth.startUartService();
+input.onButtonPressed(Button.A, () => {
+    if (connected == 1) {
+        bluetooth.uartWrite("HELLO");
+    }
+});
+```
+
+### Video - UART service guessing game
+
+https://www.youtube.com/watch?v=PgGeWddMAZ0
+
+### Advanced
+ 
+For more advanced information on the micro:bit Bluetooth UART service including information on using a smartphone, see the [Lancaster University micro:bit runtime technical documentation](http://lancaster-university.github.io/microbit-docs/ble/uart-service/)
+
+### See also
+
+[Bluetooth SIG](https://www.bluetooth.com), [Bluetooth on micro:bit resources](http://bluetooth-mdw.blogspot.co.uk/p/bbc-microbit.html)
+
+```package
+microbit-bluetooth
+```