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Topic: Wrong voltage (Read 889 times) previous topic - next topic

bill516

Jan 10, 2013, 01:53 pm Last Edit: Jan 10, 2013, 02:09 pm by bill516 Reason: 1
I like a total dork manged to put 12v down the 5v out line on my pro mini, and let some smoke out.  Now the question is, is it fixable, I know its not really worth fixing as they are quite cheap items anyway but I do like to have a go.  So what is likely to have gone phffft, I assume the 5v reg will not be very well but will anything else have gone.

Thanks for the input, Bill

Just tried the loop back test and nothing came back,  I think my pro mini is toasted

johnwasser

First thing to do is look for the components that look burned.  You can try replacing those components and hope all the damaged pieces have obvious damage.
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Krodal

Remove the voltage regulator and apply +5V to the +5V pin.
If the ATmega doesn't work, throw the board away.

The voltage regulator might be the first thing that will be broken.
Some capacitors might have been smoked. But if they don't shortcut, you don't have to remove them.
Some ATmega and ATtiny chips have survived higher voltages like very shortly 8V or so, but 12V is probably too high.

James C4S

Keep in mind that if you replace the failed component now, that does not mean others are fine.  Damaged components don't always fail at the time of damage.  Later on down the road you might be troubleshooting a problem caused months before.
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bill516

Removed the 5v reg and no change.  Is there any way to check the crystal? I only have a logic probe and a multimeter, and a big hammer.  I've got other pro minis but they are in use in other projects and a mega 2560 that I pulled from a project that is on hold.

smeezekitty

Most likely the atmega is fried at 12v if it was connected for anything more than a few mS (at best). The absolute maximum ratings on the device is 6 or 6.5v IIRC.
Avoid throwing electronics out as you or someone else might need them for parts or use.
Solid state rectifiers are the only REAL rectifiers.
Resistors for LEDS!

bill516

Well it looks like the most technical of tools I have the big hammer.  Thanks for the tips and hints, next time I'll be more careful

cr0sh


I like a total dork manged to put 12v down the 5v out line on my pro mini, and let some smoke out.


When you did this - was the power on the line?

I ask this, because what should have happened was:

1. All power is off and disconnected from the Arduino (and circuit, as needed).
2. You turn on your power supply, and adjust it for proper voltage(s) and current output.
3. You turn off your power supply.
4. You hook up your circuit to your Arduino.
5. You hook up the wires for power to your Arduino (and circuit, as needed).
6. You double check everything: Verify that all wires are in the right place, nothing isn't touching where it shouldn't, etc.
7. You triple check everything: Again - verify your connections. Are the power wires for the correct voltage hooked up properly?
8. You cross your fingers...and apply power.

Ultimately, steps 2, 6 and 7 should save you from making such a mistake. It isn't foolproof, but it is certainly better than having live power wires of unknown voltages dangling around. You should never hook up a live power source to a circuit; you should instead hook it up, then -turn it on- (after verifying connections). You should also avoid "probing around" in a live circuit with your fingers or with a test meter/tool. If you must probe with a test meter, use only a single probe (with the other probe connected to whatever other test point or ground point is needed for the testing). Keep your other hand away from the circuit (this is called the "one hand in pocket" rule).

Now - you may think all of this is overkill - after all, it's not like you'll hurt yourself with 5-12 volts DC, right? In general - no. But get into the habit now - because you might find yourself "playing around" with higher voltage circuits in the future - and in some cases, you won't generally get a second chance if you screw up on them...
I will not respond to Arduino help PM's from random forum users; if you have such a question, start a new topic thread.

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