Friday, 6 April 2012

WeenyPOV on Scalextric car

Mikepea at BuildBrighton is building a Scalextric setup with a difference! One of the many features we're thinking about is a POV display on the roof of a car which will plot out a graphic image as the car moved round the track. The first test was to see if the concept would work (basically are the cars fast enough to get a decent POV effect?). To try this out I made a quick little POV circuit on a 1" square of flexible copper clad. There is a PIC16F688 directly driving 10 green LEDs and there is no trigger or synch on it (it just runs continuously)

For the first try we opened up a car and took our power from the +5V and GND pads of the programming header on the Digital Scalextric controller board inside the car. This seemed to power the POV board fine but the car itself would not work. Unfortunately it still didn't work when the POV was removed... oh crap! not sure exactly what happened there, but Mike was very good about it and offered another car...

Worried about frying another car, we took a different approach this time and added our own voltage regulator and smoothing caps, taking power directly from the diodes that rectify the AC being picked up from the track. We only had a big 7805 regulator to work with, but actually it looks pretty cool stuck to the hood with a couple of caps. Very 1970's hot rod.

More importantly it worked.. that is until one time the car rolled and the POV circuit on the roof seems to have got a zap directly from the 12VAC on the track and the PIC died, leaving all 10 LEDs jammed on. Insulation is obviously something to consider for the next time!

So was the concept proved? it seemed to work pretty well - especially on long exposure photos. I had it displaying some particularly peurile text, but it would probably work better with small graphical images...