Re: comparator with two analog switches

"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.
I found out the hard way a long time ago that TL082 would not work as a comparator.
Whether TL3474 will, I do not know.
If the purpose of the second op amp is just an inverter then depending on the required speed a single transistor might do the job
fine.
A more detailed schematic is needed, showing supply rail connections to the devices.

Maybe the Schmitt-Triggers are critical for some reason...?
(Hysteresis?) I wonder if maybe I might have damaged the switches, so
that might be it, but I can't afford to order more right now.
>
--
Christopher Howard