Control relay from Radio

Hello every one:
I am using a arduplane version v 3…3.0 with mission planer 1.28 I am trying to controll the relay pins from my pixhawk I could control them during the mission using do_set_relay command ,but I need to control them using the radio ,i couldn’t find way to do that the radio can only control till channel while the relay start from channel 11 any suggestion.

I have a 16 channel radio/receiver and I can set either channel 8 or channel 9 which is my Gear or Ruder switch. This is set to turn on port 54 on the Pixhawk which is attached to a MOS FET to turn on LEDs.


On the Pixhawk it is labeled as Aux Out 5 and is connected to the bottom pin for signal.


dear iseries
thank you for ur reply .
I couldn’t find a parameter “ch9_opt” how can i set it ???
i am using the SPKT/DSM port using 9 channel reciver , I can control from the radio from channel 5 to channel 9 .

i can control ch 9 “AUX 1” from radio when its set as a servo “BRD_PWM_COUNT =2” while when set BRD_PWM_COUNT =0 it must be changed to relay but it doesn’t, either its not a servo any more. can u help me controlling ch 11 using gear switch or AUX2 or any other switch ???
best regards

In Mission Planner on the Config/Tuning screen select Advanced Params. Check the Advanced Menu View.

Select the Full Parameter List

It should be in the list there.

Using passthrough is not the same as relay option. RC9_FUNCTION=1
This will not work with relay option and needs to stay at 0.


Dear mike
thanks for ur reply ,i am using arduplane v3.3.0 and mission planner v 1.3.28 ,i couldn’t find the parameter “CH9-OPT” in the full parameter list .
when defining a pin us a relay i use RCx_function = 0 ,when using us a servo i use it in pass through mode .more over i have been trying all combination ,in these parameters (BRD_PWM_COUNT,RCx_function,relayx)
parameter ch9_opt could solve the problem ,but its not in my full parameter list .

Sorry I was looking at the Copter parameters. Doesn’t look like there’s an option for plane to do that even in 3.3 where there was additional options added for 9, 10, 11, and 12.

Previous version allowed Channels 7 and 8 to do that in copter.


You could get a cheap PWM controlled relay e.g. from Hobbyking.

Dear StefanG
I know i could use a PWM controlled relay ,but why if there is a relay in the pixhawk ,since you are admin ,does this mean that there is no way to control the built in relay through the radio ???
best regards . :question: :unamused:

No, that means that I am administrating the forums and the server :slight_smile:.

There is no relay IN the Pixhawk! The Pixhawk can CONTROL an external relay through output pins but if you do that, you should still have an external driver circuit for safety reasons, to prevent a spike back into the Pixhawk from the relay coil and if you anyways use some kind of external circuit, you can as well use a PWM controlled relay :slight_smile:. You can then use DO_SET_SERVO in your mission to control that.

I think the issue here is there is no relay option in the Plane version of the flight controller. I would hope that in a future version they would add this option as it is there in copter.