Relay not functioning as expected with Kakute H743 Wing

[tec2user (Andrew Carlson)]

I am trying to use a relay to communicate with a raspberry pi, and I was trying to get a constant 3.3v when the relay is triggered and 0v when the relay is disabled. I believe that I have all of the relay configured properly because when i press the switch I get an output just not as expected.

This is my Relay pin configuration this is tied to PWM 8 or GPIO57 I have also tried using IOT1 (83) with the same output.

This is the RC input configured to relay 1

This is the output I get when connecting the oscilloscope this is when the relay pin is pulled low

This is the output I get when connecting the oscilloscope this is when the relay pin is pulled High

This is the servo configuration.

SERVO_FUNCTION: -1
RELAY1_PIN: 57
RC7_OPTION: 28

when the relay goes high it sends a 3.3v spike and not a constant 3.3v output and when the relay goes low it sends -3.3v instead of staying at 0v is this the indented behavior? if so what kind of relay can I used to get a constant 3.3v when the pin is pulled high and 0v when the pin is pulled low, or is there a different way that I can configure ardupilot so that I get the same behavior?

[dkemxr (Dave)]

Ch 7&8 share a Timer group, try 9.

[jreise-d (Joerg)]

You have set oscilloscope input to AC, set it to DC and then you can see the correct 0v and 3.3v.

I have tested your relay config on my matek h743wlite and it works correctly. Timer group is not important in this case. I have tested servos on output 7 and 9, and the relay on output 8, it works. Output 7-10 are on the same timer group.

[dkemxr (Dave)]

Surprised to see that. But, if it works…

[jreise-d (Joerg)]

I thought my Matek h743wlite and Kakute H743 have the same timer groups, but they have different. Sorry, my mistake. But it works, pwm and GPIO on the same timer group is not a problem.

[tec2user (Andrew Carlson)]

@jreise-d you where correct the scope was set to the wrong coupling and the relay was functioning as expected.

M7 and M8 are on the same timer according to the holybro documentation, but they are on different channels and this doesn’t seem to affect the relay pin at all.