
Building an Analog Computer (1999) - mindcrime
https://www.clear.rice.edu/elec301/Projects99/anlgcomp/
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nickpsecurity
This is more of an analog circuit. Here's some links to analog computers,
specific and general purpose. The computing in empty space concept is
particularly interesting. One of these is very practical with a huge speedup
on numerical computation on the cheap.

Posted links to all here:

[https://www.schneier.com/blog/archives/2015/07/friday_squid_...](https://www.schneier.com/blog/archives/2015/07/friday_squid_bl_488.html#c6701962)

Wikipedia has links to old ones below. The mechanical ones trip me out.

[https://en.wikipedia.org/wiki/Analog_computer](https://en.wikipedia.org/wiki/Analog_computer)

Another little-known use of analog is obfuscating trade secrets in ASIC's. One
hardware engineer that used to post on Schneier's blog told us how most
engineers and tools did digital with little understanding of analog or
especially combinations of the two ("mixed signal"). So, he would put parts of
the critical algorithms in analog with odd tie-ins to the digital side.
Integrating their I.P. with digital tools was still easy but ripping it off
required analog or mixed-signal experts spending a lot of time. A trick worth
remembering.

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flohofwoe
The Vintage Computing Festival in Berlin which ran this weekend had a room
dedicated to analog computers, most of them still working, with instructors,
demo programs and one could even play around with them. A 'program' is
basically a set of wires that connect blocks like oscillators, integrators,
filters, etc... you started with some mathematical formula you wanted to solve
(mostly some integration problem), translated this into a 'block diagram',
built this with wires, and then you could fiddle around at the dials and knobs
and see how the result changed on an oscilloscope. I was told that this was
mainly used to simulate how complex real-world industrial systems like coal
energy plant components would behave under extreme conditions. At least that's
how I understood it all :)

Here are 2 photo I took of Eastern Block analog computers:
[https://twitter.com/flohofwoe/status/650324920862441472](https://twitter.com/flohofwoe/status/650324920862441472)
(the grey one was from 1975, which was really late in the analog era, it was
only used for educating students who had to work with older analog computers).
And more impressions from someone's blog with much better image quality:
[http://blog.awsm.de/post/130463580578/vintage-computer-
festi...](http://blog.awsm.de/post/130463580578/vintage-computer-festival-
berlin-2015-impressions)

Also interesting: the Soviets built analog water computers starting in the
late 1920s which could solve specific problems so fast that digital computers
needed 50 years to do the same thing in comparable time:
[http://www.digitaljournal.com/article/338106](http://www.digitaljournal.com/article/338106)

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yodaoryack
Analog computers are fun, there are even "universal" ones :
[https://en.wikipedia.org/wiki/General_purpose_analog_compute...](https://en.wikipedia.org/wiki/General_purpose_analog_computer)

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Animats
Of course they had noise problems. They were using a solderless breadboard.
Analog computers require shielding, good ground planes, and bypass caps on
power at each IC.

I once had two 555 timers, set up as oscillators, on a solderless breadboard,
and they'd phase-lock just from inductive coupling if they were near the same
frequency. Without bypass caps at each IC, they'd phase-lock even when the
frequencies weren't close, at some ratio like 7:6. When the big power
transistor in a 555 switches, it introduces a transient, which gets into the
input signals. Fun to watch on a scope.

While you can build analog differentiators, they're so noise-sensitive that
they're almost useless. Combined differentiators and low-pass filters can
work, but a pure differentiator tries to track the slope of every tiny noise
event. Analog computing is usually all integrators, summers, and multipliers,
as they did here.

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vmorgulis
I can add the fascinating work of Ivan Sutherland about "clockless computers":

[http://www.cs.virginia.edu/~robins/Computing_Without_Clocks....](http://www.cs.virginia.edu/~robins/Computing_Without_Clocks.pdf)

