Put your favorite flasher under environmental control

The original Versatile PIC Flasher (Dec '02) Christmas Star decoration was well received, perhaps because it contained much variety. It was controlled by a PIC16F84A microcontroller, of which eight pins were used as pulse width modulated (PWM) outputs. These constantly shifted in phase to each other, so generating a random effect on the various light emitting diodes. The five dual-in-line (d.i.l.) switches provided a choice of different speeds and modulation depths.

Following the original publication, Quasar Electronics introduced a kit for it in which they replaced the transistor output stages with a single i.c. (ULN2803) containing eight Darlington drivers. These drivers support a higher collector voltage, enabling even more l.e.d.s to be chained, and the use of the ULN2803 reduced the design to a very compact form.

It subsequently occurred to the author that speed and modulation choices do not necessarily have to be set by switches. Why not make the display externally controllable? It could even be made responsive to the environment! For example, noise level could control the speed – the noisier the faster. Perhaps temperature could control the modulation; when it is cold the Star, or other form of display, could be hardly changing, but as the temperature increased it could become more active. And how about a proximity sensor to send the Star into its “shimmer” mode?

Of course, as an instrument of measurement, resolution is limited to two digital bits, those controlling speed and modulation, but the fun factor is the real point of this project. It would be possible to talk to your Star, and get a response, or tell the temperature, or for it to burst out flashing if someone passes nearby!