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Author Topic: Apply External Vin Power Backwards on Arduino Mega 2560 R3  (Read 1118 times)
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The title of my topic says it all.

I was desperately testing different codes for my mobile robot, all of a sudden I hooked up the wires from my 7.4V  @ 1Ah LiPo battery in the Vin and GND pins backwards and then my board crashed  smiley-eek. I didn't look up at the wires polarity properly cause I had been doing that for days but s**** happens. smiley-red

Fortunately I could use it again, powered it via USB cable, but given the circumstances I'll need an external power source. The thing is that I don't know what component has been damaged; thought it could be the voltage regulator, but if anyone could give me an advice on this, I'll truly appreciate it.

And even more if there is a way of fix it, even though it sounds pretty difficult.

Thanks in advance
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Rodolfo Aguilar

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If the board presently works using USB power but does not work using Vin power because of your reverse polarity 'brain fart', then the two likely components to change is the voltage regulator and the 47ufd cap on the input to the regulator.
See schematic, upper left section.

In the future you might consider wiring your external voltage source to a DC power plug and just connect it via the DC power connector on the board, that would have protected you from reverse polarity as it has a series polarity protection diode.

Lefty

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Thanks for your time.

Do you mean these...



???

Regards
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Rodolfo Aguilar

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https://www.dropbox.com/s/w80uupelq1m968l/voltageregncap.jpg?m
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Rodolfo Aguilar

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Correct regulator but not correct cap. It would be a larger 47ufd electrolyic cap near by, called PC-1 on the schematic.

http://arduino.cc/en/uploads/Main/arduino-mega2560_R3-schematic.pdf

Lefty
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Thanks again,

This one...

https://www.dropbox.com/s/fxf7sy8mvlho0z0/47uFdcap.jpg?m

Right? Sorry I shoulda noticed thats a cap before.

Cheers
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Rodolfo Aguilar

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Thanks again,

This one...

https://www.dropbox.com/s/fxf7sy8mvlho0z0/47uFdcap.jpg?m

Right? Sorry I shoulda noticed thats a cap before.

Cheers

Most likely seems to be the one.

Lefty
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The voltage regulator should be at 3.3V or 5V? I already replaced for one at 3.3V. And its not working yet with my battery... I'll apreciate your response.

Thanks
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Rodolfo Aguilar

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The voltage regulator should be at 3.3V or 5V? I already replaced for one at 3.3V. And its not working yet with my battery... I'll apreciate your response.

Thanks

The 5V one, and it feeds the input to the 3.3v one, so the 3.3v one can't work if the 5v regulator is bad.

Lefty
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Like I told you in the last post I replaced the original NCP1117 voltage regulator for a generic one. I thought the problem was the output voltage that seemed to be at 3.3V but turns out there's a wide voltage range that works for.

The problem was that the one I replaced it for has a different pin configuration and that was the reason it didn't work at the first try.

Today I got a new voltage regulator with the same pin config than the original, replaced it and No, it's not working yet. smiley-cry

So I don't know whatelse can I do? I think I'm out of ideas.

Regards
« Last Edit: March 04, 2013, 07:05:13 pm by rodolf0 » Logged

Rodolfo Aguilar

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Anyone could give me a hand on this?

Please!!! I'll really appreciate it

Cheers
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Rodolfo Aguilar

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What is the part number of the replacement part, what is the voltage at both it's input and output? does it still operate from the USB cable?...
IN OTHER WORDS, WHAT CHANGED? WE CAN'T READ MINDS AND MY CRYSTAL BALL IS BROKEN...
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Here is the datasheet of the replacement part...

https://www.dropbox.com/s/4cwzfn4evx2c4u8/ds1117.pdf?m

Haven't checked the voltage at the input and output yet, Im out of town this weekend,

And Yes, its still operating from the USB cable.

Nothing seems to have changed by replacing the voltage regulator

Thanks for your time
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Rodolfo Aguilar

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Anyone could give me a hand on this?

Please!!! I'll really appreciate it Cheers

I've externally powered my aduino just using a standard 7805 regulator chip connected to +5v pin and ground. Not sure how this would play with the USB power source connected at the same time.
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Consider the daffodil. And while you're doing that, I'll be over here, looking through your stuff.   smiley-cool

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