Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!csd4.milw.wisc.edu!cs.utexas.edu!rutgers!att!icus!limbic!gil
From: gil@limbic.UUCP (Gil Kloepfer Jr.)
Newsgroups: sci.electronics
Subject: Re: TTL to 1500 watts - query
Summary: Oh no...a programmer with a screwdriver?!
Message-ID: <505@limbic.UUCP>
Date: 7 Jun 89 15:31:31 GMT
References: <1164@garcon.cso.uiuc.edu>
Reply-To: gil@limbic.UUCP (Gil Kloepfer Jr.)
Distribution: usa
Organization: ICUS Software Systems, Islip, NY
Lines: 29

In article <1164@garcon.cso.uiuc.edu> kline@tuna.cso.uiuc.edu (Charley Kline) writes:
>in the part that's going to have to take the delicate little TTL
>signal from my shift register and use it to turn on and off a
>1500-watt lighting instrument.  A mechanical relay is right out
[...]
>there's this thing called a triac which is essentially two SCR's
>in parallel and facing opposite directions. I figure this is what
>I want to use (but please correct me if I'm wrong). The problem
>is that I have no idea how to connect this thing.

A good (and my favorite way) to hook high voltage stuff to a low voltage
circuit, like TTL, without the potiential of frying my TTL circuit is
to isolate the two circuits using what is called an "opto isolator".
This is a chip with a LED and phototransistor placed back-to-back.
You hook the LED to the TTL circuit (via a current-limiting resistor,
of course :-) and use the transistor on the other side to send a signal
to some high current/voltage passive device.  I'm not sure exactly how
this would be connected in your application, but I definitely wouldn't
hook TTL directly to a semiconductor which is connected to house current
(except in a switching supply...or something like that...).

>Charley Kline, University of Illinois Computing Services
>kline@tuna.cso.uiuc.edu
>{uunet,seismo,pur-ee,convex}!uiucdcs!uiucuxc!kline

-----
| Gil Kloepfer, Jr.
| ICUS Software Systems/Bowne Management Systems (depending on where I am)
| {icus,lilink}!limbic!gil   or    gil@icus.islp.ny.us