Designing for cool

I have not posted any little technical tips lately, so here is a tip to make your micro-controller based projects suitable for the cool shelf and not the nerdy shelf.

Just as low voltage micro-controllers appeared that can be run on a 3V power supply which is easily attainable from a couple of AA batteries, so appeared blue and white LEDs at affordable prices, with their inherent forward voltage of more than 3V.

Blue LED tyre light on a car wheel

Cool gadget

Society has now decided that white LEDs are cool, blue LEDs are super cool, and violet LEDs are really mega cool. It has become very easy to visually identify how cool your gadget is by what colour it lights up when you turn it on. Clearly anything that has an orange, yellow, green, or dare I suggest red LED is just old fashioned and nerdy.

Designer clock with red light emitting diode display

Less cool gadget

This has resulted in a design choice with not always the coolest outcome. Your choices are:-

– You can increase the supply voltage by adding an extra couple of AA cells, probably making it a bit heavier, but getting enough voltage for a cool coloured LED.

– You can use an unfashionable coloured LED.

– You can play the green card and not use an indicator at all.

Here is an alternative, a way to run your voltage hungry cool coloured LED from 3V using little more than software and ten pennies worth of components:-

Circuit diagram showing how to connect a blue LED to a three volt microcontroller

How to drive a blue led from a three volt micro-controller

All you need to do is provide an anti-phase square wave output on the two port pins. This can be done as an interrupt routine or as part of a polling routine in software quite easily.

With careful selection of which pins you use you may even be able to use an on board peripheral like a PWM generator or timer to generate the signal.

Careful selection of the capacitor values and adjustment of the mark/space ratio of the output square wave will allow you to adjust the brightness of the LED in software for added kudos to take you up another level on the cool shelf.

Suzie x

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2 Responses to “Designing for cool”

  1. Jenny Alto Says:

    I cut my electronic engineering teeth and received my qualification before blue LEDs were invented and back then I remember being told that they were the Holy Grail and would never happen in our lifetimes.

    I thus will always see them as inestimably cool, no matter how tacky and cheap the applications for them become.

    A voltage doubler is a neat solution.

  2. Suzie Tall Says:

    They said no blue LEDs and no room temperature superconductors. Hopefully my next tip will be on a good use for Yitrium-diddlydum speaker wire!

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