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From: jans@tekchips.TEK.COM (Jan Steinman)
Newsgroups: sci.electronics
Subject: Re: TTL Questions
Message-ID: <1469@tekchips.TEK.COM>
Date: Fri, 17-Jul-87 13:53:09 EDT
Article-I.D.: tekchips.1469
Posted: Fri Jul 17 13:53:09 1987
Date-Received: Sat, 18-Jul-87 18:27:47 EDT
Organization: Tektronix Inc., Beaverton, Or.
Lines: 25

<<<1.  What's the easiest way to go about interfacing a TTL output (from, say, 
a standard S or LS AND gate) to a relay, for controlling anything from 
automobile (12VDC)...>>>

My favorite is TIP120 (?) which is a power darlington.  With just one or two mA 
base current, it will drive 8 (?) or so amps.  Who needs a relay?  Just ground 
the emitter, hook you load between the source and the collector, and drive the 
base through about 4.7k.  You can parallel them for more current if you put an 
anti-current-hog resistor between emitter and ground.  About .1 ohm should do 
-- I simply put 10A fuses in each emitter, which seems to add a suitable 
resistance.

 <<<...to house (120VAC) environments?>>>

Use a MOC2010 (?, available from RS) triac-opto-iso driving either another 
triac of the proper rating, or a relay.  There's an ap note on the back of the 
blister-pack.

<<<2.  I've... seen that a no connection to inputs, such as a simple AND or OR 
gate, drives the input high.  Is this guaranteed true?>>>

I'm afraid I don't understand this at all!

:::::: Software Productivity Technologies    ---    Smalltalk   Project ::::::
:::::: Jan Steinman N7JDB	Box 500, MS 50-470	(w)503/627-5881 ::::::
:::::: jans@tekcrl.TEK.COM	Beaverton, OR 97077	(h)503/657-7703 ::::::