I have the Frsky D4R-II Receiver in PPM mode, signal comes out from Channel 1 and RSSI comes out from Channel 2. You can have RSSI displayed on OSD by connecting it to the FC or OSD directly.
However one since the RSSI signal is PWM, a digital form, you need a low pass filter to convert it into analogue voltage level. I didn’t use one and just connect them directly, it works, but the RSSI data is pretty inaccurate I must say. It changes very infrequently, and basically only jumps between 0 and 100.
Apart from getting this info from the telemetry port, I also recently found another way of getting RSSI value, which is more accurate, you can even get rid of that RSSI output wire. If you are running PPM, and has a spare channel, you can assign this channel RSSI and send it back to your RX. Then you can configure your Cleanflight to recognise this channel as RSSI value. Finally you can setup the MinimOSD to get RSSI reading from Cleanflight, and display it.
This method also works for SBUS.
Configuration on Taranis – RSSI value in PPM Channel
First of all set up a input in Taranis.
I call it “rssi”, and choose “RSSI” as the source. Leaving all other settings as default. Setting Scale to 100.
In Mixer, we choose a spare channel, in my case I chose Channel 7.
If you are not sure and don’t want to upgrade firmware, just use 6 or fewer channels in PPM.
I name it “rssi”, and I chose the input we just created which was also called “rssi” (it has an highlighted “i” icon before the name).
Note that a channel output should have range between -100 to 100. With default weight of 100 and offset 0, the RSSI channel output will only be 0 to 100. Therefore I have made Weight 200 with offset -100.
We can now check the RSSI channel output. This is when the receiver is switched off, and RSSI iis 0% (output is -100)
And now if I turn on the receiver, we are getting a pretty strong signal.
Important Note! (12/07/2015) With Frsky D4R-II receiver, make sure you have the latest firmware installed to use more than 6 channel PPM. Basically with the old firmware, where the signal width was 18ms, it caused problems when you use more than 6 channel in CPPM. The new firmware resolved the issue by using 27ms signal width. Some shops sell the RX with new firmware, check with them first.
Configuration on Cleanflight – RSSI value in PPM Channel
First make sure RSSI_ADC is disabled, as we are not taking RSSI reading from RX directly.
Now go to the Receiver tab, and choose a channel you have created for RSSI data.
Once you have saved it, restart your FC, and you should see the RSSI in configuration info tab showing the correct, accurate and real time value. This can be confirmed in the Receiver tab as well.
Configuration on MinimOSD
And finally, if you are using MinimOSD with MWOSD firmware, you can check ‘Use FC RSSI’. Note RSSI Max need to be changed to 255, and Min to 0.
NOTE (16/Apr/2016): Since MWOSD 1.6, the Max RSSI has been changed to 1023, no longer 255.
Important Note (Aug 2017): If you lose signal, your RSSI might get stuck at a value and does not change. You might become confused why you lost control but still getting good RSSI value. Here is how to avoid this problem:
Check on the receiver tab which AUX # your RSSI signal is.
After that go to the failsafe tab. All AUX channels are by default set to HOLD, they will just keep the last value when you switch off the radio. Set the correct AUX channel in failsafe to SET 1000 and save.
After this is done the RSSI will show 0% if your radio is off.
Thanks to Szper in the comment for this.