Alright, I feel I’m getting close to pin-pointing if this a real thing or not…
Here’s a log and screenshot with Buzzer Disabled and LED Low.
The LED Low setting doesn’t seem to be visually any different to high or medium, but anyway I’ll leave it at low.
This indicates there’s no issues with Vcc related to pre-arm, fail-safe or disarmed, with the Buzzer Disabled.
Before I rejoice, I’ll do another flight with Buzzer Enabled to see if the issue returns:
obviously if the buzzer is causing the Vcc variations then at least we know what it is and how to disable the buzzer.
If the problem doesn’t return with the buzzer, then it must have been something else that’s changed…
Alright, what’s going on? I officially don’t get it.
Just did a test flight with Buzzer enabled and LED low, no sign of Vcc variations during pre-arm or fail-safe.
No other wiring or anything changed, firmware and all still the same…
Correction: some time back when removing the Pixfalcon power connector and joining wires directly to the board, I added an external connector (balance plug style) and a 22uF tantalum capacitor at the new connector - possibly this gives the 5vdc (Vcc) enough guts to maintain it’s level while LED and Buzzer are both in use, such as in fail-safe conditions.
Edit: I only added the cap to the new power wiring in the last week or so, there’s still logs in this discussion that display the symptoms even after I had replaced the Pixfalcon power connector (since this post on 22/09/17 Logged voltage varies after failsafe).
Maybe the combination of buzzer enabled and LED high would cause the variations? Maybe another test flight coming up.
So for now I’ll be leaving buzzer enabled and LED on low, since the buzzer is very handy and the LED is essential.
Probably should put this thing to bed! I can no longer correlate the variations in Vcc with repeatable events. Maybe it’s because I removed the Pixfalcon power connector and soldered wires direct to the board and added a capacitor across +5v and 0v. Maybe it’s times of the day or phases of the moon… No other wiring changes though.
Here’s a graph from today that seems to show Vcc variations only AFTER landing from fail-safe, and not during failsafe or before arming like in previous logs (before I did any wiring changes). Battery voltage and current didnt have any unexpected variations. Conditions were windy.
If anyone’s interested enough, I’ll upload the actual log.
If you see variation in Vcc related to Fail-Safe events or while not armed, test with buzzer disabled and LED disabled individually.
If the variations go away, decide how much you need the LED or buzzer.
Even though the variations might not be going low enough to cause a brownout or other issues, it’s probably a sign you’ve got problems with the power connectors, wiring or the power brick/PDB.
I’d suggest any strange variations in Vcc should warrant investigation of your power supply and connectors anyway.
The Pixfalcon has JST-SH connectors (I think) and they’re very tiny, might be a reliability issue there. I’ve pretty much eliminated the variations by soldering power wiring direct to the Pixfalcon board and adding a polarised cap across the supply. Your own remedy may be much simpler than mine depending on your flight controller and connectors.
This pic from earlier in the thread demonstrates the problem, so you don’t have to read all the way through the thread:
