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restting the counter
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my first parallel port project
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restting the counter

@ Mon Jun 12 22:29:08 PDT 2006
tagged with electronics

In the basement with Michelle's machine :-p It's so very cute! I want one of my own. One day. Rev B Black Macbook..

This is my week off before ———. Eek! Picked up my last check from ———.. right into the bank and no doubt will be bill fodder. Gurp.

Revisiting my counter circuit. I found how to 'debounce' (mostly) the connection, the 555 (which I already knew) and a capacitor + resistor in parallel connected in series to the trigger switch. The cap absorbs excess 'switches' (as it charges) and the resistor discharges the cap.. or something like that.

So now I needed a reset button to bring the counter back to zero. The 7490 has a pin that when removed from +5v resets the counter. To build a reset switch, I needed either an (a) normally closed momentary-open switch or (b) a NOT gate.

I found a nice TTL NOT circuit here:

  http://www.play-hookey.com/digital/experiments/ttl_inverter.html

Literally, transistor-transistor. I used 2N222As instead of the 2N4124s. Works like a charm. Now all I need is a tilt switch and I'll be ready to move it off the breadboard and onto a PCB. Wh00t!

After I finish this, I think it would be neat to do the same thing again but this time with a PIC or an Amtel tiny micro, just for fun. I would like to use something I can program easily w/o having to spend $$ on a special programmer. The miniPOV kit I have has a parallel port on it, and is programmable thataway, so ... that might be the way to go. I'd also want to find a way to drive multiple 7-segment LEDs with a single chip.. If there was a "two-BCD-in-to-two-7segment-out" chip, that would work for me ...