# [sdiy] Understanding Analog Computer Schematics?

Donald Tillman don at till.com
Wed Feb 25 07:32:10 CET 2009

```   > From: Aaron Lanterman <lanterma at ece.gatech.edu>
> Date: Tue, 24 Feb 2009 12:07:44 -0500
>
> Hmmm... Actually shouldn't the response be a quadratic and not a
> sinusoid?
>
> > harrybissell at wowway.com wrote:
> >> A resonant filter triggered with a pulse, followed by an absolute
> >> value circuit. Vary the Gain, the Resonance, and the Frequency ???

Um, this is an important point here...  The analog computer program is
not a resonant filter through an rectifier.  The idea is not to copy
the appearance of a bouncing ball, the idea is to derive the
differential equations, implement them on the analog computer, and be
impressed that the result looks much like a real boucing ball.

The analog computer program runs a parameter voltage (gravity) through
an integrator (velocity) and a second integrator (position), with some
feedback (damping).  So it's not an exponentially decaying sine, it's
a quadratic, or at least a quadratic when the damping is set to zero.

(That point being made, yeah sure, then they add the absolute value
circuit, the 90-degree high frequency sine, and the ball-squash-diode
for the visual effect.)

I found the manual and schemetic for the Heath Analog Computer here:

http://ed-thelen.org/comp-hist/vs-heathkit-ec-1-analog-computer.html

A bouncing ball program is included at the end of the manual.  But,
looking at it, I don't believe that program is correct.  Additionally
there are a couple simplifications you can do so that you can include
both the quadrature ball outline oscillator and the bouncing ball
program together in the 9 opamps.

-- Don

--
Don Tillman
Palo Alto, California
don at till.com
http://www.till.com
```