

Home Electrical Device Control How-to (2003) - brudgers
http://tldp.org/HOWTO/html_single/Home-Electrical-Control/#INTRODUCTION

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analog31
That brings back memories. I used the parallel printer ports of two MS-DOS
computers to run my graduate thesis experiment.

I remember a little program called "aacircuits" for drawing those ASCII-art
schematics, still useful for sticking a schematic fragment into a comment
block in a program.

But I also remember almost burning the lab down. What is almost always lacking
from descriptions of projects to control _things_ with PCs is any
consideration of safety, including what happens when electronic components or
software fail. For instance a failure mode of relays -- mechanical and solid
state -- is to get stuck in the ON position, leading to a run-away system.

I think that some sort of introduction to fail-safe design should be part of
basic education.

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mcmancini
I seem to recall one could damage a computer easily by interfacing through the
parallel port without isolating correctly... Doesn't look like this guide
covers the pitfalls.

~~~
Gracana
There's a current limiting resistor and a back-emf protection diode across the
relay coil, that's nothing fancy but it ought to be enough.

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mschuster91
Ew. This guide is missing _any_ information about isolation and safety
requirements :(

