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Author Topic: Zero Ampere on Digital outs..  (Read 443 times)
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I think I may have trashed my Mega2560

(total newbie, so Im hoping I measured correctly)
I can measure voltage on my digitial out pins, but no ampere.
I also have an uno and a simple (blink) sketch running on both gives me on the
  UNO 4.8-5v 10 ma/amp (not sure what is correct amp /10a or ma...)
and on the
  MEGA 4.8-5v 0 ma/amp..

There is not enough power to power a led or anything..

Is there a way to double check this?

Thx.. smiley-red
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Be sure to measure correctly:

Amperes are measured through some resistor with a DMM(Digital MultiMeter)

+5V (pin HIGH) ---- DMM  ---- [ 10 K ] --- GND.

should read:  I = U/R => 5 /10.000 = 0.5mA
The DMM has virtually no resistance.

if you do
+5V (pin HIGH) ---- DMM  ---- GND.

the DMM will shortcut the system and thats not good.

As Arduino can deliver 50mA per pin if I recall correctly the resistance of the device(s) connected should be at least 100 ohm .



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Rob Tillaart

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1) PIN(on High) -- 10K Resistor -- +wire (multimeter) -wire -- GND
or
2) PIN(on High) -- 10K Resistor -- GND
                         |                       |
                          ---- + DMM - ----
Just to be sure..
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sorry I meant..
PIN(on High) --  +wire (multimeter) -wire -- 10K Resistor -- GND

dont seem to be getting a reading whatever..

It may be wrong but when I connect my DMM to directly from pin to ground I get a reading on my UNO and not on my MEGA
connecting an led works with the UNO and not with the MEGA although I can read volts with both..
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Do the UNO and MEGA use the same power supply or do the have their own? try to swap?

Is your MEGA capable of doing this simple sketch?
Code:
void setup()
{
  Serial.begin(115200);  // or 9600
  Serial.print("Hello world");
}
void loop(){}

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Rob Tillaart

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Yep I have tried USB & 7.5v Extern
sketches work fine.. get a serial response from both, the MEGA just simply does not seem to have enough power to light up  the a simple led..

I may have shortened the mega somehow If i connect directly from a 5v to GND I get a reading and the led works, however if from a pin on HIGH to GND I get a reading from 5v (4.8-4.9) but it does not power an led..

Is my understanding correct that I can read voltage but there is no amperage to power something..

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Problem found ... had a short on the back of the board (using screw mounts) and I think my incapability of measuring amperage
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