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Topic: Zero Ampere on Digital outs.. (Read 568 times) previous topic - next topic

garyd

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:

robtillaart

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 .



Rob Tillaart

Nederlandse sectie - http://arduino.cc/forum/index.php/board,77.0.html -
(Please do not PM for private consultancy)

garyd

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

garyd

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..

robtillaart


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: [Select]

void setup()
{
  Serial.begin(115200);  // or 9600
  Serial.print("Hello world");
}
void loop(){}


Rob Tillaart

Nederlandse sectie - http://arduino.cc/forum/index.php/board,77.0.html -
(Please do not PM for private consultancy)

garyd

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..


garyd

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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