Gents I need your help.

I recently upgraded one of my 2.6APM powered quads to a Pixhawk.  One of the reasons I went ahead and did this is because the Pixhawk is supposed to take PWM RSSI signals directly (into the Sbus port aka Pin 103) and I could ditch my PWM to analog conversion circuit is used in my APM.

I have verified that my EZUHF receiver is outputting RSSI in PWM form on one of the channels. (it will move a servo appropriately when the RF gets weak or disappears... and it worked fine for the APM as an RSSI input via a PWM to analog conversion circuit)

And, I have hooked up the PWM RSSI output to the Sbus port (pin 103).... it does nothing.  Shows zero RSSI on the OSD no matter what.

I can't find any useful description of how to configure this in the wiki, mission planner or this site.

How do you make a Pixhawk show RSSI from a PWM input on pin 103 as its advertised?

Thanks for your help.


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Some context for my post above from the Pixhawk overview.

Virtual Pin 102: Servo power rail voltage. This is an internal measurement of the servo rail voltage made by the IO board within the Pixhawk. It has 3:1 scaling, allowing it to measure up to 9.9V.

Virtual Pin 103: RSSI (Received Signal Strength Input) input pin voltage (SBus connector output pin). This is the voltage measured by the RSSI input pin on the SBUS-out connector (the bottom pin of the 2nd last servo connector on the 14 connector servo rail). Can alternatively serve as SBus out but not yet implemented.

per the pixhawk overview

  • Extensive I/O interfaces with dedicated connectors
    • Fourteen PWM servo or ESC speed control outputs.
    • Five UART (serial ports), one high-power capable, 2x with HW flow control.
    • Two CAN I/O ports (one with internal 3.3V transceiver, one on expansion connector)
    • Spektrum DSM / DSM2 / DSM-X® Satellite reciever compatible input: Permits use of Spektrum RC Transmitters.
    • Futaba S.BUS® compatible input and output.
    • PPM sum signal input.
    • RSSI (PWM or voltage) input.
    • I2C and SPI serial ports.
    • Two 3.3 volt and one 6.6 volt Analog inputs.
    • Internal microUSB port and external microUSB port extension.
    • Contains its own on board microcontroller and stacks with the FMU.


Hi Did you ever solve this?

I have a PIXHAWK and a Futaba T8FG and would like to buy a EZUHF for the futaba and then a 4CH RX or the 8CH diversity and use the PPM. Only it will suck to pay 260+ bucks and not have it work. 


The PPM output from the EZUHF works nicely with both APM 2.6 and Pixhawk.  I highly recommend the EZUHF radio gear.  I have 4ch, 8ch lite, and two 8ch diversity receivers.  All are used for 8 channels (including the 4 channel one) via PPM sum output on channel 1.

The current "issue" I am having is simply that the PWM (pulse width modulation) output for RSSI or Link Quality that can be sent from the EZUHF receiver  has to go through a special home made circuit to turn the PWM signal into a readable analog signal so the APM or Pixhawk can get signal strength or link quality to show up on my OSD.  I have used 1cell non-brushless speed controllers from hobby king for this for the last year with the APMs and I'm sure it will work ok with the Pixhawk too, I'd simply prefer a direct connection. (as they promised)

I did hear  from Craig at 3DR that the PWM input for RSSI will be included in a future software release...he did not indicate which one... I have not yet looked to see if it is on the list for 3.2 which is at least 6 weeks away according to Randy.

There is an easier way. I have a EZUHF and see RSSI on my minimosd but i have a APM. The trick is to config the EZUHF rx to send the rssi as PWM over a channel. It doesnt matter which, just pick one of the high ones like 5 - 8. The APM wont know its RSSI it will think its just another regular channel.

You can config this using the Immersion config tool. You can then config minimosd-extra to read rssi over that same channel. The minimosd-extra config tool has this option available.

The only downside is that you lose a channel between the rx and the apm. However i still have 8 channels coming thru i simply connect one directly to my gimbal to control the tilt. I thus end up with 7 + the rssi going to the APM and one from the rx to my gimbal.

Its simple and works, no extra hardware or fancy analog to digital converter type bits.


Thanks for the tip, (I set ch8 to output RSSI, which it is doing), but I don't see how to tell the MinimOSD to read ch8 as the RSSI channel in the config tool.

I am running minimextra config tool and version 2.3 copter in my quad.

Which screen do you find the RSSI channel selection in the config tool?  I don't see it.

What setting if any do i need to make in MP?

Thanks for your help.

Ok, I figured it out...MinimOSD to the rescue!

I needed to update the config tool to 2.4r727 and the corresponding firmware for minim OSD... now my RSSI (link quality actually) shows up on my OSD with no extra hardware.

This is exactly what I wanted.

Good stuff, minimosd-extra is always evolving, its always worth grabbing the latest of all the artefacts and trying them because new stuff is always appearing.

Does anyone know if or when the RSSI over PWM feature will be delivered?

Hi Steve,
Wow, the hours I have worked to get RSSI from my pixhawk ( plane, not copter ) on my minim OSD !
And as of today, still no luck.
I have been following this thread and have followed all of the steps to achieve RSSI from my Pixhawk to my minim OSD.

On the minim CT , I set the rssi pin to channel 7, (and accordingly set the RSSI ppm output channel on the receiver to 7 as well )
Rssi is still reporting a non changing value of -99 on the screen , regardless of the transmitter being on or off.

I checked the actual output of the rssi by connecting a servo to the no 7 channel and the servo moves when the rssi changes, so I know channel 7 is outputting a proper pwm signal representing the rssi.

Is there something else you did in MP to effectively get the pixhawk to "see " the rssi ?

On MP, I tried setting the RSSI pin parameter to " pixhawk" (103) ,nothing. Tried typing in A7 for analog pin 7,nothing. Tried the other "A" numbers in the drop down box, but no changes.

I am 5 plus hours into this and completely baffled. Your help would be GREATLY appreciated !!


Just had the same issue - APM 2.5.2 and MinimOSD - looks like on CH7 the RSSI is not working in MimimOSD, on CH8 it works though. EZUHF, PPM Muxed, RSSI on CH8. Only problem now is that its reversed ...


There a couple of "gotcha's" in the setup.  

1) this works with 2.4r727... not the earlier releases

2) despite the ability to select different channels the minim OSD software only works with channel 8.  (I think this is where your problem is)

3) I feed the PPM sum stream to the pixhawk, not individual channels.  I suspect it will still work with individual channels but my setups are all via a sum stream... 

There is nothing you need to do in mission planner to make this work.

I suggest setting the ezuhf signal quality to channel 8 and you will be good to go (other than calibrating it.)

A couple other suggestions...  I prefer signal quality to RSSI because it is possible to have really strong signal strength but poor signal quality... this happens when you have things like the camera putting out noise on the 433MHz band.

To find zero and 100% set the minimosd to raw first and write down the numbers that appear when you switch the transmitter on and off... this will give you the figures to calibrate full and null signal... then go back into minim OSD put those figures in and remove the raw number switch... 

Sorry for the frustration on this, but it can be made to work

Thank you for the quick response ! I will try changing to channel 8 , and hopefully get some results ...thx again.

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