Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!uunet!sco!deanr
From: deanr@sco.COM (Dean Reece)
Newsgroups: sci.electronics
Subject: Opto-Isolator Advice Needed
Keywords: Opto-Isolator CMOS TTL
Message-ID: <5020@scolex.sco.COM>
Date: 1 Mar 90 02:02:17 GMT
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Reply-To: deanr@sco.com (Dean Reece)
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Organization: The Santa Cruz Operation, Inc.
Lines: 32


I'm building a circuit to control various functions on my audio/video
equipment by computer.  I realize that isolating my circuitry from the
existing A/V stuff is a really good idea, so I need some advice on the
use of opto-isolators.

The basic requirements are low power/low (electrical) noise switching.
The input side is to be driven be either 74LSxx or 74HCxx (I haven't
decided yet).  The output side is going to simulate a keypress on
the equipment, which is a standard momentary N.O. switch which completes
a path to ground when pressed.  Speed is not really a requirement, so
anything in the 1 ms (milli-sec) range is plenty.  As for logic levels,
the 74 series part I'm using to drive the opto-isolators is an 8 bit
addressable latch (7f[HC|LS]259) which can be cleared to all Lows; so
a low input to the isolator should result in a key-released condition
(not grounded).  The controls being tickled are themselves inputs to
CMOS controller chips, so 15 volts or so is all thats being dealt with,
though it would be nice to have a large margin (say 60 volts).

So... I'm asking for your favorite Opto-Isolator circuits to do the
above.  If you've got a known solution or a good reference, please
let me know (via email - I can summarize).  I would prefer to keep
the range of devices being used down to the easily available & low
cost ones available from Jameco, All electronics, Digi-Key ...

Such as: 4N25, 4N26, 4N27, 4N28, 4N32, 4N33, 4N35, TIL-116, TIL-154

Thanx in advance
 ______________________________________________________________________
| Dean Reece     Member Technical Staff |"The flames are all long gone |
| The Santa Cruz Operation 408/458-1422 | but the pain lingers on"     |
|___________deanr@sco.com_______________|___________________Pink_Floyd_|