APM RSSI 3.3V input


For some time I wanted to add ability to provide RSSI from FrSky receiver to APM.

RSSI_PIN parameter works fine for that however some of receivers such as mine FrSky D8R-XP outputs 0 - 3.3 V. For that purpose I've added new param and called it RSSI_RANGE.
This was also issue requested before: https://github.com/diydrones/ardupilot/issues/648
After voltage rescaling it works. rxrssi is shown in scale 0-100.

And added ability to rescale in params:


Here few pictures:



I've used 4.7k resistor and 10uF capacitor to filter pulse signal coming from receiver's RSSI output.



Hope this helps anyone.


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  • To anyone still reading this, I semi-solved my jumpy reading problems by removing the resistor from my filter. Turns out openLRS receivers already have a resistor, so they only need a filter. Still, I get about 10 points jumpyness :(
  • John80, you were probably running AC 3.1, which does not have the feature. Try with 3.2!
  • Where can I fond this RSSI_Range parameter? I am running the latest Mission Planner with the latest quad firmware. 

  • I'd say anything more than 10v is fine. Keep it low though, don't go to 35v+...
  • What voltage 10uf capacitor is best....16v?

  • This is the rx working in this way, the MP just processes the input data. I had a similar problem - my rx gives the ~1V as min and 2V as max and when it off the value jumps so I made the voltage level convertor and realise program filter which analyzes the data for 1 second and calculating the mean value, so I get the refresh rate of 1sec and some protection from short spikes of the voltage.

  • So, I made the cable, with cap and resistor. I do get values on the OSD but they're a bit strange. Especially when my Tx is OFF, the reading jumps around a lot.

    I've used the "view raw" setting but still, when tx is off it jumps about 30%...
  • Thanks Anton, but I don't get what you say. My RSSI out is 0-3.3V. Can I just connect this to APM?
  • Still wait for possibility to set the min and max voltage value as rssi min and max to configure rssi out with MP for proper data displaying.

    Chris Mavrakis
    Currently there is to ways: 0-3.3V and 0-5V corresponds to 0-100%. If your rssi voltage from 0 to >3.3V than the divider will help.

  • So copter guys have to wait for 3.2.

    I'm wondering, is there a way to make it work on 3.1? Maybe a voltage divider to drop the 3.3V down to what the APM "by default" thinks is 100% signal?

    What's APM's idea of 100% signal, in voltage?
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