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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  • There is no arducopter 3.2 yet. In 3.1.2, RSSI_RANGE is a Pixhawk only feature.

  • RSSI_RANGE on arduplane is present on MP 1.3.0.

  • I just see the RSSI_PIN and then its followed by RTL_ALT

  • Hi,

    i have MP v1.3 and running v3.2 arducopter but I can't seem to find the RSSI_RANGE parameter in the Full parameter list.

  • Hi.
    I use RX700LR and it give me the ~1V as min and ~2V as max RSSI value. After I set the 2V in RSSI_RANGE, it is ok for the 100% signal but when the RX is off I see the ~50%. How can I tune the MP to proper data displaying. I this is not possible now, it will be great to see this feature (ability to set the min and max voltage value) in future. Also the MP don't show me the "rxrssi" at the green screen, but it show at "status" parameters. I use the latest version 1.2.97.

  • Hello.....I have a Frsky Delta 8 rx which can output PPM on ch1 to my APM 2.6 ch1.  The control link is working great.

    The rx can also ouput PWM rssi, but I am having trouble getting it to appear on MP hud.  MP is current at 1.20.97 and APM is current at 2.78b.  I have RSSI_PIN=0 and RSSI_RANGE=3.3.  When I measure the signal-to-ground volts on rx ch2 signal pin it is pretty constant at ~2.85v.  If I turn the tx off the volts on ch2 pin drop off sharply to around .03-.07.  I realize this is a PWM output and Frsky manual says specifically that is is a "Digital PWM" output.  So I have read many many post on DIY and other internet sites that show various "RC filters" and "digital-to-analog converters".  I have tried several combinations of resistors/caps and schematics (not tried op-amps yet since not getting signal from green light).  I simply cannot get the "rxrssi" field and any rssi value to show up on MP hud, even if I feed 3v straight to the A0 or A1 signal pin.

    Regardless of whether I am getting the correct rx rssi output from Delta 8 rx, or whether I am using the correct rc filter or dax, I simply dont understand why the hud rxrssi field doesnt show up on the hud when a constant analog 3.24v dc applied to apm A0 or A1 signal pin.  Any help is appreciated.  I know I must be overlooking something.




  • By the way, this circuit works with the Pixhawk if you plug it in the SB input and set RSSI_PIN to 103 (ArduCopter 3.1.2-rc1). RSSI_RANGE set to 3V

    It could be added to the Wiki

  • Admin

    In this case it is in middle of both. So probably won't offer the advantage to either or both :). Capacitor closer to brownout-ing device would make sense to me

  • In my opinion it make more sense to put filter closer to apm , that way you don't have voltage drop due to wire length, and there is less chance for interference. In general you should keep this wire-circuit as short as possible. 

  • @p.r. as detailed in the image above, the resistor is closer to the receiver, capacitor connected in parallel after the resistor, closer to the APM.

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