Unexplained reboot while un flight

[interestingfellow]

So not cool!

F22 scratch build dtfb/stick plane, orangerx switchable dsm/walkera module, opentx 2940, turnigy 9x, spektrum 6xxx rx.

I crashed my f22 and had to retrim the plane. While trimming out ailerons (mode2) my 9x just...rebooted. i only got to press the trim switch 2 or 3x and bam, reboot. Plane was crashed on the ground, so tried the aileron trim button again, and again, 2-3 presses and it rebooted AGAIN. Now I can't reproduce the issue...


Does anyone know wth happened?

This tx combo has never given me an issue like this.

[Kilrah]

Well known design issue on the 9x.

viewtopic.php?f=95&t=3594

[bob195558]

As you read (viewtopic.php?f=95&t=3594), when get to 9x Radio Rebooting Problem Horizontal Trims Digital Ground Fix,
shows a way to fix the rebooting problem: (viewtopic.php?f=95&t=3594&start=120#p69475).

Bob B.

[interestingfellow]

Thanks! I had no frickin idea that was an issue. I was brand new to 8ch+ tx's when I got the 9x, and didn't find any major issues like this (obviously, I missed this one!) when researching before buying.

So, I have to cut the ground trace for the horizontal trim buttons, and reconnect them to the ground trace for the virtical trims? I'm going to continue reading; I want to know understand *why this happens.

Also, I appreciate your assistance and patience with me when I posted earlier. I was posting from my phone, in a rush, concerned as hell, and had to get back to work.

Thanks, y'all!

[MikeB]

With the original MEGA64 processor this didn't show up, only when the MEGA128 is fitted does it become noticable.

I think the threads referred to above explain reasons why this can happen.
Basically, the horizontal trims use the analog ground instead of the digital ground, and when you switch a trim, a capacitor wired across the switch (also a poor design) discharges through a small indcutor and causes an electrical spike that can cause the reboot.

Mike.

[interestingfellow]

I haven't traced it out on the schema or in my tx, yet, but rather than cutting traces and soldering jumper wires, wouldn't it be easier to just remove horizontal trim gnd wire from the plug that goes to the mobo, and piggyback that to the digital ground wire? Or are there other components tied into that horizontal trim ground that this would effect?

[MikeB]

The (analog) ground connection to the horizontal trim board is also used as the ground for the gimbal pots, so you must not move it to digital ground or the gimbal will most likely jitter.

Mike.

[interestingfellow]

ahhh, that totally makes sense! (as it pertains to just switching a single ground wire around)

[interestingfellow]

...How is this issue fixed in the AR9X board?

Or is the AR9X chip less picky about digital vs analog ground, and it doesn't matter?

[MikeB]

The big difference is the AR9X runs from 3.3V, so when you press a trim switch, the capacitor only discharges from 3.3V to 0V instead of 5V to 0V. This is a lot less energy, so any spikes are much reduced. In addition the digital and analog ground signals are common.

Mike.