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Rooting around in the fascinating stuff at the bottom of a draw labelled 'Engineering - Junk Miscellaneous'. Delving amongst the delightful...

An Engineer in Wonderland – Led Christmas lights

cc-xmas-led-lights.jpgSee all ‘Engineer In Wonderland’ posts

I was rigging up some Christmas lights and in a fit of enthusiasm thought that flashing would be good.

So I drew out a multivibrator, then wondered what other two transistor circuits would also flash some lights.

Mr Google delivered this rather good site which gives chapter a verse on the subject of two transistor oscillators.

The disappointing part was, it looks like the good old standard circuit best suits my needs, so no exotic new oscillator to play with.

I have 20 parallel red leds, and 20 parallel blue leds, and a source of constant current.

03dec08alicelights.jpgBlue leds have a higher forward voltage so I reckon if I connect the red leds in parallel with the blue leds, but with a transistor in series with the red ones, then turning the transistor on-off will flash the leds red-blue.

If I get around to building it, it will be a PNP multivibrator with one collector load connected not to the negative rail, but to the base of an NPN medium power transistor.

If I don’t find time to build it, I have still learned a lot about multivibrators.

Alice.

Respond below, or to alice@electronicsweekly.com

(Picture – Our LED Christmas lights by rtadlock, under Creative Commons Attribution Licence)

Tags: creative commons, engineer, google, led christmas lights, rigging

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1 Comment

  1. June 30, 2009 22:39

    That’s cool you used my picture in your article. I was wondering why this picture got so much traffic. :) Thanks for the mention at the bottom of the article, and good article.
    Rob

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