This is a discussion re the bad Accel, Gyro and Baro values that we're seeing with ArduCopter-3.1. The increase in the SPI bus speed from 500khz to 8Mhz has exposed a hardware problem on some boards. That hardware problem is that the 3.3V regulator has been blown so all sensors are running at 5V instead of the intended 3.3V.
How have these regulators been burnt out?
- Attaching a radio receiver or MinimOSD to the APM while the APM is only powered through the USB (see video below)
- Some clone boards seem to come from the factory with blown regulators. 3DR boards might also come with blown regulators although they do a specific check of the regulator as part of the regular QA process.
- It is not (as far as we know) actually caused by the AC3.1 software itself, it just exposes the problem. You could prove this to yourself by checking the 3.3V regulator (see video above) before and after the upgrade.
How can we fix the regulator?
Option #1: If it's a new board (so that it's less likely you burned it out yourself) you could report the problem to the retailer that sold you the board and ask for an replacement. If it's 3DR it's called an "RMA".
Option #2: if you're handy with a soldering iron you can replace the regulator yourself. On the APM2.5.2 (and higher) boards it's not that difficult. On the APM2.5 it's far more difficult.
For APM2.5.2 : TPS79133DBVR
For APM 2.5: MIC5219-3.3YML TR
How can I stop it from happening again?
Do not connect any devices such as a radio receiver, MinimOSD, GPS, etc while the APM is powered especially while powered only through the USB cable.
Attaching a 100uF capacitor across any of the APM's radio input's 5V and GND pins will stop the regulator from being blown by plugging in a receiver. video here!
There are very few reports of regulators being blown twice and no reports of it ever failing in flight.
Below are some graphs of the types of values that we are seeing on these boards.
Replies
unfortunately this is not solved. Please all, DO NOT TRY THIS SOLUTION YET.
We ARE investigating this very issue at the moment, and will inform you of any findings. There IS an issue with the shifter, but it is the Data lines that are wrong not the Vcc lines
the 3.3v VCC is rated to MAX 4.5v, so connecting this to the VCC 5v as suggested here could lead to an unknown situation.
Please wait for some results from our testing first.
I agree with Philip, its not the Vcc lines to the voltage level translator it's the data lines that are at the wrong level if the eagle file is correct.
http://www.ti.com/lit/ds/symlink/txb0104.pdf
VccA must be at a lower voltage than VccB - which is correct in the eagle layout. If you do the proposed fix as Guaifi posts then you would violate this condition and maybe damage or leave it non functional?
A-side signals are the low voltage signals. B-side signals are the high voltage signals - that's where it is wrong in the layout. The B side (should be hi = 5V) actually is connected the the 3.3V data-flash lines? Unless I am overlooking something?
Keep in mind, this goes back to the beginning of the APM2.5
This fault, has not caused an issue due to the fact that flash can handle the higher voltage.
This will be fixed on the next layout revision, but it is not considered a critical issue.
I would guess if Guaifi still had 5V on the 3.3V supply with the 3.3V regulator removed and cutting the Vcc A & B lines to the level translator chip has helped to get rid of the 5V then maybe his voltage level translator had and internal short/failure?
I would guess having the signal level swapped it only stresses the voltage level translator since Vin on the A port is rated at max 4.6V - don't know how high or stiff the ATMEGA CPU 5V output would be to give it a sweat. Since it is translating a communication line its probably by the nature of the signal safe to ignore besides that shifting level is not working.
YES, you are correct:
I didn't tried yet the dataflash because I couldnt solder the 2 red wires changing 3.3 and 5V so my level shifter is OFF and my dataflash is not working for now.
Also, dataflash never worked (with firmware 2.9b before cutting lines) so it was bad from factory.
But I checked all the rest and that was the problem.
Also, I didnt checked which one (A or B ) side of the level translator is the 3.3 or 5v but sure you are right and data lines are the problem and not the power lines. But, changing all the data lines in that chip is IMPOSSIBLE! SURE!
And about the people who ask me why about others ¿?¿? I don't know, maybe there are diferent batch of PCB. Mine is from HobbyKing, color black. Weeks ago I didn't understand why other people change the regulator and said that it worked but mine not changing or putting one external....
Also I didn't realice that I was flying with version 2.9b and 5V on all sensors (LOL!)
I only want to contribute, there is a problem in my board with the level shifter, I solved mine (except for the dataflash). Try yourselfs.
Maybe, if your problem is having 5V on 3.3v regulator AND your dataflash doens't work this is the solution. For other cases, check.
Sorry about my english (but sure you understand better than my spanish).
Guaifi, I think its a great find!!
Its just not the cause for the general failing 3.3V regulator problem that's discussed here.
Not to mention, that if this was it, 100% of boards would have the problem 100% of the time.
So, I'm not sure about this one. Let's have some other people look at it before declaring anything. This is already spreading like wildfire...
But it could help to explain quite a lot of these voltage issues.
Just for your info, here is the scope trace on the Digital servo
2v per div, 50ms per div
Max voltage over 10 Volts
see my comments above regarding this.
if the servo is on ch9-10-11, then this would go straight back onto the vcc 5volt rail
Out of curiosity what brand servo and BEC do you use?
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