Lumen light will be off when the motor run

I used Ardusub firmware v3.4 and connect light to rc9. when i changed the pwm value through joystick,the light will be brighter or dimmer normally.
But when i operated the propellers, the light will be off. once i did not operate the propeller, the light will be on normally.
I also connected the light to Arduino and set pwm value to 1700, when i operate the propeller, there is no effect.
I think when i operate the propeller , the pwm value of rc9 will be affected.


Can you please take a picture of your electronics, and a picture of the back of the Pixhawk, where the motors and lights are plugged in?

Hi @qdxiatao,

Can you also please tell us which frame version you are using? Did you download the firmware for vectored, bluerov, vectored-6dof?


i use PX4-vectored v3.4 downloaded from
motor 1-6 are connected to channel 1-6.
camera servo is connected to channel 8
light is connected to channel 9

@qdxiatao - Okay. Can you send a screenshot of the lights setup page in QGC? I’d like to make sure they’re configured for the right channel.

If i use arduino to receive pwm value from pixhawk and then control led, it is normal. the pwm value output from aruidno is normal when i operate propeller.
pixhawk is powered by ESC
very strange!

#include <Servo.h>
int buttonPin = 13; //read pixhawk pwm value from ch9
byte servoPin = 9;
Servo servo;

void setup() {
servo.writeMicroseconds(1100); // send “off” signal to Lumen light

void loop() {
int pwmValue = pulseIn(buttonPin, HIGH);

I have just confirmed with an oscilloscope that servo Pin 9 is operating as it should in this configuration on ArduSub 3.4, whether or not the motors are armed.

How are you powering the light? Are you sure that that green wire is spliced well?

Why aren’t you using Main servo output 7? If you use that pin, you can see the pwm value on the pin under SERVO_OUTPUT_RAW in the mavlink inspector.

Another note is that we recommend using QGC 3.1 with ArduSub 3.4, you might want to try that.


If you are still having the problem, please save your parameters by clicking the ‘Tools’ menu in the parameters tab of QGC, and send them here.

Hi @qdxiatao,

How are you powering the system right now? If you are using a low voltage battery or a low-current power supply, it’s possible that the voltage is dropping below the usable point for the lights, which is about 8v.