Tuesday, November 29, 2005

Arcade Electronics

So where do you go when you need a DB25 IDC connector right away? Arcade Electronics, which is just north of Springfield. Lots of good electronics, reasonable prices, no shipping if you just show up and buy it.

I stopped by Scott Hutchison's studio last night. We are evaluating whether we like the behavior of Look better with active IR sensors or passive IR (PIR)sensors. The jury is still out.

PIR sensors for home security systems generally operate like a relay. If there is "no intruder," they are either "normally open" circuit or "normally closed" circuit.

I'm always scared of blowing out PC parallel ports, so instead of using potentially hazardous voltage pull-ups and pull-downs to detect whether relays are open or closed, I hook the relay between a parallel port output and an input. I then drive the output up and down a few times. If the input pin follows the output pin every time, you know the relay is closed. Otherwise, it is open.

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