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Home Brew Analog Computer System

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GK:
Ever since stumbling across the awesome stuff on show at this website:

http://www.analogmuseum.org/english/


...... I've been working like a man possessed to design and build my own solid state hybrid digital/analog computer to modestly put virtually all of those extinct commercial offerings to shame (complexity, size, precision, etc).

I've just completed the preliminary design of the Sine/Cosine Function module. The completed computer will be equipped with 8 of these modules. On the Patch Panel it is simply two-port black box which spits out either (depending on the mode setting) the Sin or Cosine of the applied input voltage (Ein), multiplied by a scaling factor (K) of 100. It has (for an analog circuit) a very high degree of accuracy and stability).

Transfer function equations and limits are given in the text on the schematic *.pdf. I'm just sharing the little circuit because I'm rather chuffed with it. Log/Antilog, dividing, squaring, square rooting is all easy-peasy stuff. The sin/cosine function module however is one I've been scratching my head over the most. Once I figured out how to practically implement the necessary slope inversion (at the 90 degree and 270 degree points for sine) with a high degree precision, the cat was in the bag.

Unlike in the current simulation file, the final circuit will have a power hybrid discrete HV op-amp with a short circuit proof output stage and a +/- 10mA drive capability. The input impedance is 1M, shunted with 20pF or so.

The attached charts show the transfer characteristic in sine and cosine mode, with a full scale Ein ( 0 to 360 degrees).
 

poptones:
That's very cool. I'd love to see a detailed writeup about the theory and operation.

SeanB:
I used to have a box of mechanical sine/cosine resolvers and hundreds of other styles of synchros and resolvers, they were parts of anb autopilot. We were cannibalising them for spares to fix moving map displays and other synchro indicators

GK:
Those must have been interesting devices.

Don’t have time for a explanatory write up right now, except that the circuitry based on the LT1097 op-amps in the left hand half of the schematic forms a “function generator” (in analog computer speek) that produces a dual (polarity) slope, asymptotic approximation (with break points at 90 degrees and 270 degrees) of either a sine or cosine function from the applied, uni-polar input voltage which represents phase angle. A bipolar, multi break-point curve-shaper then does the rest.

I’ve started refining the circuit, to begin the transition from LTspice to Protel. Firstly, I had to get rid of that huge series string of LT1634 voltage references to bias the break-points of the curve shaper. That is NOT very economical; and especially so when one intends to build 8 of the things. I’ve decided to use a separate pair of dedicated supply rails of +/- 50V, exclusively for biasing the break-point shapers of all sine/cosine modules instead. The intermediate break-points between +/- 50V are now provided by a 0.1% tollerance resistor ladder/divider.

Much cheaper and even more accurate as the +/-50V can be accurately trimmed for “perfect” symmetry. The regulator will be a hybrid op-amp/discrete deign based on the LT1097 precision op-amp for the error amplifier, deriving the +/-50V form the separately regulated +/-105V rails.

I’ve also added another pair of break-points to the curve shaper to improve the accuracy of the curve fit around the +/- peaks.

Attached is the revised preliminary schematic, along with a plot showing how well (for now) the break-point shaper approximates an ideal sine curve, by plotting it against a perfect/ideal sinewave source.

alanb:
I don’t know if anyone else remembers but a long time ago ( late 1960’s I think) Practical Electronics published a series of articles on the construction of a simple analogue computer. It was very basic but was a good introduction to analogue computing. It kept me occupied for many months and was where most of my pocket money was spent during the period.

If anyone still has a copy of the articles they would be great to see again.

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