RSSI to channel output

I know this has been covered before and i myself have done it but i simply can't remember how and i searched and searched but couldn't find the post.
In Betaflight i want to set the rssi to a channel output so i can have it displayed in the osd i found videos on how to set it up with a Taranis but can't remember how to do it with my 12s..Would like to use ch12 for the rssi value if anybody could please help me remember how to do this please reply..
Thanks all..
<Marty>

For FrskyX it's configured by the RSSIChan protocol option. Click the protocol name on the model page to access the options. The following information was recently added to the manual:

RSSIChan: When set to LastChan the received RSSI will be transmitted on the last radio channel. The last channel is based on the # of Channels setting in the model. The channel value is the received RSSI value multiplied by 21.

Thanks for replying i believe i have it working now cause it shows the RSSI in the configurator ..Setting up a F3 in a wing running INAV but still have to hook up the camera/vtx to verify it shows on the osd..
Is there any way to get the last ch to show the value on the page config like a slider ect..? I have the last ch on the screen as a slider but it doesn't move when the rssi goes up or down..

So glad i found this! Got it working but why is the RSSI value multiplied by 21 rather than just sending the telemetry value?

I have a Devo 7e with a 4 in 1 module. My flight controller is an Omnibus F3 using an XM± receiver connected to the flight controller using SBUS. These receivers have upgraded firmware that transmits RSSI on a dedicated channel 16. Mine had firmware that does not have this feature on channel 16 and because I have a Devo 7e and not a Taranis radio, I can't flash the receiver.

So...I was thrilled to see that this can work on any Betaflight aux channel but I've had no success. I see the updated Devo 7e manual that says the channel value needs to be multiplied by 21 to get the correct RSSI value.

1. I have no idea what this means. What channel value?
2. How should the mixer be configured?
3. I've set the FrskyX protocol to RSSIChan to Last chance using 16 channels but in Betaflight I see no response on Aux 12 (channel 16). How should the Devo 7e be configured?

Thank you

The XM+ does not support telemetry. Since it doesn't send anything back to the tx, there is no rssi value to put on the last channel. It seems like the only options are to flash the XM with an FTDI device or use the XM's hardware RSSI output.

Hexfet, thank you for the reply.

"...or use the XM's hardware RSSI output"
Can you please expand on this? What is the MX's hardware RSSI output?

BTW... this is one description of using an ftdi device:
www.reddit.com/r/Multicopter/comments/6x..._xm_without_taranis/
This is beyond my ability so am very interested in the alternative you are suggesting.


Again, thanks.

I'm not sure the hardware RSSI solution is any easier. Run the XM+ RSSI hardware signal into an RC filter, then connect that to the FC. Then configure betaflight to use the RSSI_ADC feature.

The XM+ has a hardware RSSI output pin, but couldn't find much documentation about it. According to this site the output is PWM so you'll need an RC lowpass filter on it before feeding it to betaflight.

Betaflight has a capability of analog RSSI input, but again didn't find much online. See the last section on this page .

Thank you very much for this detailed explanation.

Question: is it fair to say that RSSI is not all that critical when flying FPV using 5.8ghz equipment because the 2.4ghz frequency that is measured by RSSI has a far greater range than the 5.8ghz video frequency used by FPV. Therefore the video will fail before the rx/vtx fails.

Note: I bought 2 XM+ receivers at different times. In both cases the vendor sold them as having RSSI on channel 16 but in both cases it is necessary to flash the XM+ with the correct firmware from the Frsky web site. I'm unable to do that with the Devo 7e.

Finally, I love the Devo 7e with the 4-in-1 module. I also think the XM+ is great even without the RSSI capability.

Once again, thanks for the comprehensive reply.

I own the XM+ and to my testing, the so called on board RSSI output does not work with or without RC filter. It just toggles between 3V and 0V. Actually it seems to me the LED output is a closer indication of radio signal strength as its blinking rate is dependent on the signal strength.

The firmware specific PWM RSSI at ch8 or ch16 is the only reliable way to go for.

MikeNH wrote: Question: is it fair to say that RSSI is not all that critical when flying FPV using 5.8ghz equipment because the 2.4ghz frequency that is measured by RSSI has a far greater range than the 5.8ghz video frequency used by FPV. Therefore the video will fail before the rx/vtx fails.

This isnt accually always true, I made a mistake testing VTX antennas and realised too late that the flying direction took me behind a lot of leafy trees when I was far out, and then it didnt help that I was 40m up and 500m away. Lost signal and failsafe turned of the motors. Hard crash down on rocks (mostly internal connectors and buzzer that shattered on impact). I hadn't lost VTX and even though it was a bit noisy it wasnt any problem flying with it, just no control.

The reasons: 2.4GHz and 5.8GHz are basically equally bad in terrain penetration, 5.8GHz vs 433MHz would be another thing. Simple dipole antenna straight up on RC TX and the common coax antennas RX in Quad sideways up, with 100mW 2.4GHz TX. But 200mW VTX with Pagoda-2 on quad and directional patch antennas on goggles. And its transmitting very close to the RX so it will raise the noisefloor. Its simply a case of more power, much better antennas on the VTX than RC link, and less signalnoise on the receiver.