RSSI from channel 8 Failsafe

Hi,

I’m setting up a new Air frame for my son and I’m using my old APM 2.6. From my understanding the last available Firmware that still runs on the APM 2.6 is Plane 3.3. So I hope I am in the right category.

I have a new receiver, the XM plus mini (2.4GHz Taranis) which outputs SBUS. I flashed the APM 2.6 internal PPM encoder to understand SBUS and all is fine, servos work.

Now I flashed the firmware for the XM+ mini to output RSSI on channel 8, and I can see it’s working in the Radio Setup of Mission Planner.

Obviously I would like Plane 3.3 to understand and read RSSI, so I can setup the long failsafe action. My current version of plane 3.3 does not offer me to choose a Channel for RSSI, so I figured I would try it manually, via Voltage reading. I am familiar with the:
RSSI_PIN and
RSSI_Range parameters

Next I set RC8_FUNCTION to Pass-trough and tried to directly connect Output 8 with pin 5. Which doesn’t work.

Basically that is another cable, which is technically not needed and all I want is a proper RSSI reading, hope someone can help me out

http://ardupilot.org/plane/docs/common-rssi-received-signal-strength-indication.html?highlight=rssi

Regards,
Tobi