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From: dr@skivs.UUCP (David Robins)
Newsgroups: sci.electronics
Subject: Re: Gain control
Message-ID: <2808@skivs.UUCP>
Date: 19 Feb 89 07:35:09 GMT
References: <6950@fluke.COM>
Reply-To: dr@skivs.UUCP (David Robins)
Distribution: na
Organization: Smith-Kettlewell Eye Research Institute, San Francisco, CA
Lines: 11

A simple op-amp gain control is to use an opto-coupled FET, the GE
H11F1 , F2, or F3.  It is fairly linear with respect to current thru
the LED.  The FET output is floating, acting as a variable resistor,
with a voltage rating of about 27 V.  I have used it both in the input
resistance and the feedback resistance in op-amp circuits,  It is much
simpler than using multiplying DAC's or multiplexers.
-- 
David Robins, M.D.  (ophthalmologist / electronics engineer)
The Smith-Kettlewell Institute of Visual Science,  ***  net:  uunet!skivs!dr
2232 Webster St, San Francisco CA 94115            ***  415/561-1705 (voice) 
The opinions expressed herein do not reflect the opinion of the Institute!