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Support Forum » Voltage on Micro Controller Pins

May 27, 2010
by axiom
axiom's Avatar

Hi all,

I started with my NerdKit a few months ago and all worked great then. I then shelved it for a while because of college. Now, I'm just running the "led_blink" program and the LED blinks, but very very dimly. It worked fine a few months back. I checked the battery, it's still running around 8.6 V. Multimetering the anode and cathode of the LED shows only .5 V across the LED... Any ideas as to what's going on?

Thanks very much for your help!

Rob.

May 27, 2010
by hevans
(NerdKits Staff)

hevans's Avatar

Hi axiom,

My guess is your battery is almost dying. Have you tried checking the battery voltage while the NerdKit is running. Many times a dying battery will still show a pretty high voltage when connected just to the multimeter because it is under very little load. When it is asked to draw the higher currents required by the LED however you should see the voltage drop dramatically.

Humberto

May 28, 2010
by axiom
axiom's Avatar

Thanks for the advice Humberto, but the battery appears fine - while the micro is powered on it's reading 8.45 V. I also tried a different battery but similar issue. Also, there's 4.97 V between the rails so there appears to be a sufficient supply...

I get the feeling I may have damaged the crystal. I tried to bend one of its pins slightly and it made a unhealthy click. Would a faulty crystal explain the LED being dim?

Thanks again for your help.

Rob

May 28, 2010
by hevans
(NerdKits Staff)

hevans's Avatar

Hi axiom,

That is quite odd. Have you tried moving the LED to a different pin? Does it have the same behaviour.

Humberto

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