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Topic: Output broken? (Read 2192 times) previous topic - next topic

ixde

Hello,


I just wanted to start a new project and noticed that somehow, Pin 12 of my Arduino UNO (rev 3) seems to output only very low current.
So, i took my multimeter and was able to measure only .142 mA, at every other output, i was able to measure around 33 mA.
Is it a hardware issue or maybe even software-wise?

AWOL

Tell us more.
Like, how did you measure output current? (It may not have been broken before, but if you got the method wrong, it may well be now)

ixde

I measured it directly at the output jacks (between pin and ground).

All pins are about 30mA, Pin 12 just gives me ~140µA

AWOL

Quote
I measured it directly at the output jacks (between pin and ground).

How?

CrossRoads

Is the chip warm to the touch? That's usually a good sign the pin is damaged.
You do have pinMode set to Output, yes?
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

ixde

#5
May 30, 2013, 09:01 pm Last Edit: May 30, 2013, 09:04 pm by ixde Reason: 1

Quote
I measured it directly at the output jacks (between pin and ground).

How?


Multimeter (Range: 200mA, set to dc of course) -> Test prod #1 to Pin 12, Test prod #2 to GND. Before i took my multimeter, i also tested it using a LED and see if it lights up, it just lights up a bit.

Quote
Is the chip warm to the touch? That's usually a good sign the pin is damaged.
You do have pinMode set to Output, yes?


Its not warm.
Yep, set to output.

CrossRoads

What is the current going thru? Just the meter?
If so, you probably smoked the pin. The meter has a very low resistance shunt inside to act as a series element, and a voltage measurement is taken across it to calculate the current.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

AWOL

So, you shorted the output to ground via your multimeter?
(Can you see where I'm going with this?)

ixde

Hah, seems to be my fault then (I thought it would be okay to do so).

But even before i used my multimeter, i used a LED and it didnt really light up but only slightly.

CrossRoads

LED with no current limit resistor? Would have similar effect.  Poof!
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

dc42

It sounds to me that the transistor that drives the pin high is blown, but the pullup resistor is still working. The transistor that drives the pin low may be working too.
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

ixde

Okay, thank you then. I really have to be more cautious on that ;)

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