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Completed the Larson Scanner”.  Named after Glen A. Larson, the creator of both Battlestar Galactica (1978) and Knight Rider (1982), it is a simple LED sequencer that mimics the “eye” of the Cylon or the hood scanner on KITT in Knight Rider.

So what’s so special about about a LED sequencer?  A couple of logic gates would do it, a microprocessor isn’t even necessary.  This sequencer accomplished the sequencing of 8 (12 capable) LEDs with a chip with only 6 I/O lines, and only 4 were used.

This feat was made possible by “Charlieplexing” the LEDs, saving I/O pins and not overly increasing complexity.  In using a microcontroller, the pattern and speed can be easily changed.  With two left over I/O pins, other functions can be added.  Mark-II of this circuit will include left scanning, right scanning, and a “sync” signal for multiple pumpkins scanning in unison.

As you can see, the schematic is fairly straight forward.  What is different is the LEDs are not tied back to a common positive or ground.  Each end is connected to a microcontroller pin, back to back, and each pin is brought high or low, turning on the desired LED.  With n pins, it is possible to drive n*n-1 LEDs.  Stated simply, with our 4 pins, we could drive 4*3 = 12 LEDs, however, only 8 were needed.

Development of the code was also rather straightforward.  A PICMicro PIC12F519P was chosen (had them on hand) and the code turned out rather straightforward.  However I chose to “brute force” the scanning routine, there are far more elegant ways of doing it, but there was plenty of room on the PIC.  (SOURCE CODE HERE)

A cheap LED desk lamp was sacrificed for this project…

The clear LEDs were stripped out, the PCB traces cut where necessary, wires added, and red LEDs were put in place.

Finally… a suitable pumpkin was selected

Tools of pumpkiny destruction laid out…

The eye piece was fitted…

And the rest was colored in

And the final product, ready to go on the front porch…

Oh, and the base of the reading lamp was used as the battery holder.  Battery life is about 4 days before the LEDs become noticably dim.  The PIC holds up well under 3 volts.