Smoke Pump Hardware Programming


I am currently trying operate a Sullivan Skywriter smoke pump using either the servo or the relay aux pins on a Pixhawk PX4. The smoke pump’s power is coming from the drone’s battery and the manufacturer of the pump has outlined that it can be activated by a “switched channel” or “can be operated like a servo”.
I am currently using: A Pixhawk PX4, Mission Planner and a “Divention DEVO F12E” as my controller.

So far, I have attempted to plug the pump into port AUX 6 of the px4,
Then went into mission planner and set:

Config/Tuning -> Standard Params -> First Relay Pin (RELAY_PIN), I selected “Pixhawk AUXOUT6” from the drop down menu.
Under Extended Tuning, next to Ch7 Opt, I selected “Relay On/Off” from the drop down menu.

This should be varying the voltage on AUX 6 from 0-3.3v when channel 7 is being switched back and forth… however THIS IS NOT WORKING. I have confirmed by testing AUX port 6 with a multi-meter and the voltage on pin 6 does not change at all when channel 7 is flipped back and forth on my controller.

Just wondering if anyone can provide some advice here, this is my first drone build and would appreciate any input.
Is it possible to have a switch on my remote mapped to the relay command on the Pixhawk? Or should I be trying to operate the pump as a servo? All that I want to do is flip the pump On/Off via the remote while in flight.

Thank you

Graeme, just looked very quickly at the instructions, but seems (and you confirm in your post) that the pump is expecting a standard PWM signal, not a DC voltage, so configuring for a relay won’t work. You should be able instead to hook it up directly (radio connection cable) to your receiver and program the channel on your transmitter to any available switch.

If you want to hook it up to Pixhawk instead of the radio receiver you could simply use RC pass thru on an upper channel. Or you could use channel 7-9 options with, say, camera trigger (in extended turning on Mission Planner), and configuring as with a servo as in here :

Hi Olivier,

Thanks for the information. I was successful at programming some of the Aux Ports on my transmitter to send PWM to some unused ports on my receiver. Appreciate your input here.