Archive for July, 2010

Designing for cool

July 14, 2010

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


Power failure

July 13, 2010

Nowadays we are very reliant on electricity. I don’t feel the need for vast quantities of it, but just a small reliable supply would be nice.

Eleven thousand volt elecricity pole with transformer

Electricity pole

Unfortunately the reliable is not available, we get no choice of how the electricity is supplied, and the monopoly network supplier is not under any pressure to make the supply reliable.

This morning was a good example. Power went off at around 06:00. Not a big deal you might think, everyone is still asleep then. Well I was asleep until neighbour (A)’s alarm sounded.

Alarm bell box fitted on a wall


They have an alarm which sounds when the power fails, which is handy for some I guess. It is nice to know that the battery is working fine and can keep the alarm sounding for an hour or so.

It was not long of course before the power was restored for a short while. This is quickly identified to all in the street because neighbour (B)’s alarm which does not have a battery sounds when power is restored. I am sure that this is a jolly hand feature too. It was not long of course before the power failed again and you guessed it, we were back to the slightly different wail of neighbour (A) again until the battery went flat.

The blackbirds seem to find all this very amusing, because they took the opportunity to adjust their dawn chorus to include both alarms.



It must be really handy for neighbour (A) to know that should the battery go flat the alarm can still be heard for another hour or so until the blackbirds clear off to find some breakfast.

So, apart from being woken up at the crack of dawn with no access to normal methods of entertainment (telly, radio etc.) and no communication methods (telephone, internet) life takes on a rather surreal turn.

I start off by reading the rest of the Radio Times – there is not much on this coming week that anyone needs to worry about. This is followed by reading ‘The Garden’ – not too much to do in the garden in July fortunately, but good news that the worlds smallest water lilly has now been successfully propagated. Fancy having to simulate an African hot spring to make it flower!

Now that is really everything exhausted. Looks like the rain has stopped now, so Mrs. Suzie agreed that we should go out for a walk. That gets rid of a couple of  hours and can be ticked off the exercise budget. I love walking but it is so time consuming for the small return. Swimming can be done a lot quicker!

Out in the road we meet Team EDF in their pick-up trucks.EDF logo

“It is the trees, they are touching the wires and the rain has made the trees wet and shorted out the power”.

So no rain for a couple of months has made the trees nice and insulated, and allowed them to grow through the wires. In a normal world there would be some pressure on EDF to do preventative maintenance with a chain saw and perhaps get them to realise that if they replaced their aerial knitting with something neat and tidy underground we would not have the spectacle of flaming telegraph poles (which is what happened last time it snowed after a dry spell, creosote makes them burn really well when they get going!), dead birds (they sit on a lower wire and bang their heads on an upper one at a different potential) and general unreliability.

So we went for a walk. it is nice to see the flora on the beach. You would think that nothing grows there, but there is sea holly, sea kale, horned poppys,

Horned poppy on the beach

Horned poppy

and three different coloured Valerian as well as some hollyhocks that have escaped from a nearby garden. All nice things we should be able to have in the garden but have not got. Not only do they not need soil – they grow in just sand, but they don’t need any watering either and we live in the driest place in the UK.

Walk over with but still no electricity. A cup of tea is now seriously overdue, so time to move in to the caravan. It is quite a novelty to be boiling the water in a gas kettle, lighting the gas fridge, and then listening to analogue radio while we drink our tea.

Eventually the power is restored and life returns to normal. E-mail, telephone, television and an electric kettle. Strange to just slip seamlessly back into normal life. The postman has been, and my subscription copy of Model Rail is now on the mat, what wonderful timing.

Suzie x