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Home Brew Analog Computer System
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GK:

--- Quote from: saturation on December 10, 2012, 03:50:59 pm ---...... analog technique that folks buy these days in pre-made ICs  :-+.
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And digital ones just for fun  ;)

A bunch of prototype analog modules are currently on the back-burner until parts arrive, so I've made a start on the digital section of this "analog-hybrid" computer. Here is what I've called the "Iteration Counter". It's a 4-bit programmable-n counter whose primary purpose will be, receiving its clock input signal form the computers master timing/controller unit, counting problem solving iterations and, patched into an electronic analogue multiplexer network, switching different sets of "initial conditions" and/or constants for each problem solving iteration.
Just for example, suppose you "write" a program to compute and plot the trajectory of a projectile or missile. The problem can be solved/plotted/displayed successively with anything from 2 to 16 different (multiplexed) constants (just for example) for gravity. The completed computer will have four of these counter modules, which can be either daisy-chained for patched independently to perform other functions. 

All of the computers patchable digital logic will use open-collector inverted logic (0=1) with internal resistive pull-ups on all inputs. All I/O is designed to be blow-up proof, such that any I/O can be accidentally patched to a + or - 100V analog output without damage. The Iteration counter has a clock input, a reset input and 20 current-limited open-collector outputs with indicator LED's. There are sixteen decimal outputs (D0-D15) and four BCD outputs.
   
Here is a vid of it running; as shown, n-programming is achieved simply by patching the reset input to the appropriate decimal output. The 4 LED's on the far right are indicators for the BCD outputs. 
 


Schematic is also attached, as well as a more readable form the Triangle Waveform generator schematic, with a couple of errors corrected.

chickenHeadKnob:
@GK: A simple and probably stupid question from a software guy - what drove the design choice of 50V rails?, I can understand split supplies ( balanced ) just not the high voltage.
GK:
Actually the analog modules run regulated supply rails of +/- 110V, with an operating output swing of +/-100V. In analog computer speak, that makes this a "100V computer" - 100V = 1 computing "unit". Back in the day most solid state analog computers were 10V computers, with the analog (op-amp) stages running on +/-15V rails. However the Rolls Royce machines from Systron Donner were 100V computers.
The reason for this is that it is much easier to maintain a high degree of accuracy when the voltage is ramped up. Consider an integrator stage (the heart of an analog computer) based on a jfet-input op-amp. It might have an input offset voltage of 10mV. 10mV is 10 times less error in a 100V computer than it is in a 10V computer. Also, "function generator" modules such as my sine/cosine module that rely on diode break-point / piecewise waveform shapers are much easier to make accurate in a 100V design than in a 10V design, as variations in diode voltage drops and transistor Vbe's are much less significant.

A 100V computer is also 10 times cooler than a 10V computer.


Jay_Diddy_B:
Hi GK,

You might like this high voltage op-amp

Link: http://www.linear.com/product/LTC6090#overview

Jay_diddy_B
GK:

--- Quote from: Jay_Diddy_B on December 22, 2012, 02:35:54 pm ---Hi GK,

You might like this high voltage op-amp

Link: http://www.linear.com/product/LTC6090#overview

Jay_diddy_B

--- End quote ---


Unfortunately it only does +/-70V !

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Finally got the design of this solid state sine/cosine resolver completed. Might get the board dropped into the etch tank tomorrow if all this damn Christmas crap doesn't get into the way.

 
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