NerdKits - electronics education for a digital generation

You are not logged in. [log in]

NEW: Learning electronics? Ask your questions on the new Electronics Questions & Answers site hosted by CircuitLab.

Support Forum » led array test

January 16, 2010
by jastermerrel
jastermerrel's Avatar

Hi everyone,

I have constructed the led array. Upon running the test program The first 6 "anode" leds go dim as the row is lit up. So, once the whole row is lit, column 1,3 ,5 ,7, 9, and 11 will be dim but still lit. The rest "second half" of the array is fine.

Any ideas? thanks

January 20, 2010
by hevans
(NerdKits Staff)

hevans's Avatar

Hi jastermerrel,

That is indeed an odd issue, at least not one I have seen come up before. Columns 0-5 are the 6 columns that are driven by the PCx bank of pins. This could offer a clue as to what is going wrong. Are you sure you got the power connections right to right side of the chip? These are the connections to pin 22, 21, and 20 of the MCU. Miss-wiring those power connections can cause the chip to still run, but some of the power things on that bank of pins to be funky. Hope that gets you closer to finding the problem. Let us know if you make any progress.

Humberto

January 22, 2010
by Farmer
Farmer's Avatar

I want to say.... Check for shorts. I have a single LED column that refuses to light. While probing the LED leads with a "hot" wire I inadvertently taped a row wire. I noticed this short caused a "dimming" affect on the LED's in that row. You seem to be describing the same barely lit situation I noticed.

Best of luck to you

The Farmer

January 22, 2010
by jastermerrel
jastermerrel's Avatar

As Homer Simpson would say..."DOH!"

Thanks Humberto you hit the nail on the head. I had moved everything from one breadboard to another and just missed that...I guess I was too excited about getting everything wired up and sniffing too much rosin core :) The fact that everything appeared to work (except the dimming effect) threw me off.

Thanks again!

Post a Reply

Please log in to post a reply.

Did you know that a microcontroller can measure an RC time constant? Learn more...