Hein (fub) wrote,

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Quick 'project'

I found the schematic for an electronic die online, based on a PIC 16F628A. Basically, the program keeps counting from 1 to 6, and 'slows down' when the user presses a button. The seven LEDs were all direct-dive.

That is a pretty neat idea for a kit (Velleman has a kit with two dice): it's easy to explain what it does, it can be 'used', and may be a neat novelty.

But obviously, something as low-tech as direct-drive LEDs is out of the question for the fun and innovative kits I will offer! Look at it, the Velleman kit uses three ICs and eight transistors! I have to do better, which is why I will be using Charlieplexing.
The 12F675 has 6 IO pins. Take one pin for the pushbutton, which leaves 5 pins. Five pins is enough to Charlieplex 20 LEDs, which is more than enough to drive the 14 LEDs needed for two dice! Drasically fewer components (1 IC, 6 resistors, 14 LEDs, 1 button), smaller PCB footprint... All in all, a better kit.

So tonight, I built a small Charlieplexing circuit. (I needed a break from site-building anyway...) Nothing drastic, just a proof of concept. And I got it to work. Now I understand the circuit and the software needed to drive it -- so now I feel confident in using the technique in my own projects.
Tags: electronics project, webshop

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