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From: john larkin <jl@glen--canyon.com>
Newsgroups: sci.electronics.design
Subject: Re: comparator with two analog switches
Date: Fri, 25 Apr 2025 14:33:55 -0700
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On Fri, 25 Apr 2025 16:16:53 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:

>"Christopher Howard" <christopher@librehacker.com> wrote in message news:87r01gqc76.fsf@librehacker.com...
>> Hi, I am building a little 70's style analog computer, mainly for
>> learning purposes. For the most part I've been able to follow the
>> Grappendorf project schematics, but that project does not include
>> schematics for a comparator. I looked at the Anabrid THAT design
>> schematics, and I was going to make something based off that; however,
>> the Anabrid design uses Schmitt-Trigger inverters, which requires 5V
>> supply, and I was hoping not to have to mess around with 5V, everything
>> else in my system requiring only a +/- 15V. So, I was wondering if I
>> maybe I could get rid of the Schmitt-Trigger inverters from the design
>> and get by with just use op amps instead, like so:
>>
>> http://gem.librehacker.com/gemlog/starlog/img/2025/20250425_comparator.jpg
>>
>> But when I try to build this, I've seen various strange results from the
>> switches, like it getting stuck with seemingly one switch stuck open and
>> one stuck close. I've done various bits of troubleshooting, but haven't
>> got to the bottom of it yet. Is there something fundamentally wrong with
>> the design?
>
>I would avoid using op amps as comparators.


Some work nicely. It's best to try them.

My general gumdrop amp, OPA197, makes a nice RRIO comparator.