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Author Topic: External Power supply doesn't work  (Read 6555 times)
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I recently got the latest Arduino Uno in the Solarbotics (oomlout.com) Experimenter's Kit for Arduino.
I have good batteries in the external power supply, but my arduino only turns on and runs the sketches when connected via USB.
Am I missing something?
Why don't the sketches run on external power supply?
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fuzzball27 >>-->

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I have good batteries in the external power supply, but my arduino only turns on and runs the sketches when connected via USB.
Am I missing something?

What value voltage does your 'batteries' put out? The external power connector requires around 8vdc minimum to power an arduino.

Lefty
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The DC jack needs atleast 7v to put out 5v out.
Test the 5v line when it is hooked to external power.
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It should also work with 6V on DC jack according to MC33269 datasheet.
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It should also work with 6V on DC jack according to MC33269 datasheet.

There is more to the issue then just the drop out spec for the MC33269. There is a series polarity protection diode that will drop some voltage and the auto voltage switching logic via voltage divider and op-amp comparator use a fixed reference to determine when to switch from usb power to external power. I would always recommend 8vdc as the minimum external voltage to apply to the external connector.

Lefty
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Looks like that kit uses a 9 volt battery clip to barrel connector.  If you have a meter you can ohm out the connector to make sure there isn't a broken wire or check the voltage and make sure the polarity of the barrel connector wasn't wired backwards, it needs to be center tip positive.
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A small 9vdc battery is a poor choice to power an Arduino, especially if your trying to drive leds or other external devices. The current capacity of those batteries is very small and it's voltage will sag low due to it's high internal resistance. Plus they are very expensive batteries when considering the low mah rating they have.

Lefty
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Thanks for the help,
I used my handy-dandy multimeter and narrowed the problem down to poor connections in the external power supply.
It's funny how some problems are so freakishly simple.
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