Testing Copter 4.2.0 rc1 - Pre-Arm: Relay[1] Pin 55 Invalid

I loaded up 4.2.0 rc1 to test fly tomorrow morning on my EDU-450.

Mission Planner reports a pre-arm error Relay[1] Pin 55 Invalid.

I use this relay to activate the shutter on my Naked GoPro Hero-8.

I tried activating the GoPro shutter, and indeed, it failed.

I re-installed 4.1.5 and the problem went away.

I re-installed 4.2.0 rc1 just to be sure I didn’t do something wrong - but the problem returned.

I don’t know if it has anything to do with this, but about 6 months ago we had some discussion about the relays booting in “high” momentarily - and that this was under control of the bootloader - so there was no easy solution.

I don’t know if there were any parameter changes with 4.2.0 - is it OK to fly on 4.1.5, or would it be safer to wait until 4.2.0 is fixed?

The Wiki is up to date with this:

Good deal. If I missed it in the release notes, I apologize.

It is a good thing. The BRD_PWM_COUNT parameter that’s been retired generated a lot of forum posts :grinning:

I’ll study up. I’m anxious to try the new and improved capabilities. I did find it in the release notes on the first beta. My bad. I’ll study them all again.

Any idea if this change fixes the issue of the relays going “high” momentarily on boot up?

That’s a good question. I saw some posts about that a month or so ago but don’t recall the end result. It was a bootloader issue as I recall.


I just read the wiki about GPIO.

At first read it looks like my old parameters would still work. Pins 55 and 54 were relays, and I used 55 for my camera shutter.

I’ll have to take a closer look at my parameters with the wiki again.

A lot of people use pin 55 for camera shutters. I expect a lot of people will have to deal with this change.

No. That’s a boot loader issue and remains as before.

Dave - reference my post this morning - the wiki describes the use of brd_pwm_count - and it appears this parameter no longer exists - as you noted.

The GPIO wiki will be great source of confusion until this is resolved.

ADDENDUM - Looking over the wiki again, it begins with a NOTE and a WARNING box. But all the previous text still exists. This is where the mention of brd_pwm_count exists.

Its unclear if the entirety of the text below the NOTE and WARNING box should be ignored if using 4.2.0, or if one must decipher it in light of the NOTE and WARNING box.

I’ve mentioned this in my other post about this. Maybe I’ll be the only one who gets confused about this and needs a little hand holding.

1 Like

See here:

Yes, we’ve definitely got an issue with the BRD_PWM_COUNT change. Certainly at least the documentation needs updating but maybe we should also change the SERVOx_FUNCTION to -1 for some of the upper channels by default. This issue is on the 4.2 issues list.