[vcf-midatlantic] EAI TR20 analog computer exhibit

Dave Wade dave.g4ugm at gmail.com
Fri Nov 18 12:02:25 EST 2016

> -----Original Message-----
> From: vcf-midatlantic [mailto:vcf-midatlantic-
> bounces at lists.vintagecomputerfederation.org] On Behalf Of Herb Johnson
> via vcf-midatlantic
> Sent: 18 November 2016 15:53
> To: vcf-midatlantic <vcf-midatlantic at lists.vintagecomputerfederation.org>
> Cc: Herb Johnson <hjohnson at retrotechnology.info>
> Subject: [vcf-midatlantic] EAI TR20 analog computer exhibit
> SVCatITC [Bill Inderrieden] posted:
>  >> I need analog math problems to be submitted, so that when the  >> TR20
> is restored, we'll have simulations to run on the computer.
>  >> I'll make a list of what computational modules we have so you  >> know
> what to work with, i.e.  integrators, DFG's, summers, etc.
>  >> The plan is to have an XY  recorder and XY scope for results output.
> Bill and all: I've taken the liberty to post  a reply under a proper
subject line
> that's relevant to the thread. Not "digest question blah blah" which is
> irrelevant and will be impractical to search back for in the future. I
> encourage people who post, to use relevant subject lines, but this is up
> the Moderator to enforce, (except when he doesn't).
> Bill, I worked with EIA analog computers long ago, and I'm an old
> engineer. So it's good to see this EIA TR20 will be restored and
> demonstrated. But very few people in the VCFed list, have any experience
> with analog computing or with differential equations. Fewer visitors will
> know this stuff.
> The classic demo of these sorts of systems, is some kind of "bouncing
> display. Everyone has seen a ball bounce, so it's familiar. There ought to
> enough integrators to make a damped oscillator. Since you want a chart
> recorder output, the frequencies will be sub-audio.
> But you might allow for a speed-up at audio rates, so an oscilloscope and
> speaker can demonstrate operation, without requiring the chart recorder
> and using up paper and ink - all points of failure, weeks and months
>   If it were my choice, I'd go "audio" so it's easier for the docents to
> demonstrate the unit and avoid problems with chart recorders.
> That's my considerations. Something simple, familiar, and convenient to
> demonstrate when you aren't there. The amazing thing will be that it
> and has been preserved. We can run real programs, another day.
> Herb Johnson
> --
> Herbert R. Johnson,  New Jersey USA
> http://www.retrotechnology.com OR .net

I really like the car suspension problem, so typically you have a tyre which
you model as a spring, a wheel which is a Mass, and the actual suspension
which is a spring and damper. 

Then you can have parameter pots which control the parameters of the model,
springiness of spring and tyre, resistance of damper, speed of car over a

Actually, I think a problem which displays on a scope, and runs repeatedly,
so that you can see that the problem parameters can be optimized quickly.

This kind of shows why Analog Computers remained in use for so long after
the problems could be simulated on digital computers.


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