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Topic: Continuity between 3.3v and gnd (Read 379 times) previous topic - next topic

slobban

Hello there, I'm afraid that a fried my DUE :P, not fun....
I have built a my own shield from this prototyping board http://www.nkcelectronics.com/MEGAshield-KIT-for-Arduino-MEGA-2560-R3-and-Arduino-DUE_p_309.html.
When I was done with my shield a measured continuity between ground and 3.3volt, ground and 5v and between the vcc and gnd "rails" and there was no continuity what so ever. I also double checked that 3.3volt was to be used on the shield, the protoshield has a jumper which let you choose between 3.3 or 5v. All looked fine so I hooked it in my DUE and turned on the power, and nothing happens, I unplug the power source and measures continuity once more, and now suddenly I got continuity between 3.3v and gnd, but not between 5v and gnd, I then remove my shield fromthe DUE and measures continuity once more and all looks fine, then I measure the continuity on my DUE and now I got continuity between 3.3v and gnd, but not 5v and gnd, so  for some reason my "all looks fine" shield has fried up my DUE.

Should add that I used a power source of 12volts hooked into the power jack on the DUE.

So can anyone confirm that my DUE is fried, and can anyone give me some hints of what I should look after on my shield, cause something is wrong with it, but not the continuity?

MarkT

There is a switching regulator on the Due so there is an inductor between 5V and 3V3 which
may complicate measurements (although I think the standard buck topology means it will
be isolated when powered down.

Using continuity mode on a multimeter (beeping mode) is not reliable, since decoupling
caps on the board take a while to charge - use resistance measurement mode and allow
a few seconds for readings to stabilise.
[ I won't respond to messages, use the forum please ]

slobban

Hmm, so you mean that you should measure resistance between 3.3 and GND when it's powered up?

Actually I found whats wrong and I'm pretty sure that the tiny DUE is fried... The shield I linked in my earlier post holds a specified area for the i2c interface, that meas one row of is connected to SCL, one to SDA, one to the ground rail and the last one to the power rail. I didn't knew this (the traces wasn't that obvious and I didn't measure explicitly this), and I soldered a fuse holder to one of the holes connected to the power rail, the fuse holder was used for income power to the arduino, which is 12v. SO this mean that I drove 12v into my arduino backwards via the 3.3v pin. So I'm quite sure that it's fried.

Well, well a stupid, and not cheap lesson has been learned.

MarkT

Quote
Hmm, so you mean that you should measure resistance between 3.3 and GND when it's powered up?


Asbolutely not, that could blow up your multimeter.

I said use resistance measurement mode, let the reading stabilise.  Be aware that
switching regulators may be an issue since rails can be joined by an inductor which
will show up as 0 ohms at DC.
[ I won't respond to messages, use the forum please ]

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