Update Advanced_Bluetooth_Telemetry.md

docs/Advanced_Bluetooth_Telemetry.md

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-#Bluetooth Telemetry
-{The documentation goes here}
+#Bluetooth Telemetry in PPM Mode
+###Telemetry
+
+There are 4 protocols supporting telemetry: Hubsan, DSM, FrSkyD and FrSkyX.
+
+Hubsan displays the battery voltage and TX RSSI.
+
+DSM displays TX RSSI and full telemetry.
+
+FrSkyD displays full telemetry (A0, A1, RX RSSI, TX RSSI and Hub).
+
+FrSkyX displays full telemetry (A1, A2, RX RSSI, TX RSSI and Hub).
+
+### If used in PPM mode
+
+Telemetry is available as a serial 9600 8 n 1 output on the TX pin of the Atmega328p using the FrSky hub format for Hubsan, FrSkyD, FrSkyX and DSM format for DSM2/X.
+
+You can connect it to your TX if it is telemetry enabled or use a bluetooth adapter (HC05/HC06) along with an app on your phone/tablet ([app example](https://play.google.com/store/apps/details?id=biz.onomato.frskydash&hl=fr)) to display telemetry information and setup alerts.
+
+### If used in Serial mode
+Telemetry is built in for er9x and ersky9x TXs.
+
+To enable telemetry on a Turnigy 9X or 9XR you need to modify your TX following one of the Frsky mod like this [one](http://blog.oscarliang.net/turnigy-9x-advance-mod/).
+
+Note: DSM telemetry is not available on er9x due to a lack of flash space.
+
+Enabling telemetry on a 9XR PRO and may be other TXs does not require any hardware modifications. The additional required serial pin is already available on the TX back module pins.
+
+Once the TX is telemetry enabled, it just needs to be configured on the model (see er9x/ersky9x documentation).
+