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Home Brew Analog Computer System
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GK:
Hey, no worries. There are a few pages to get through now  :)
GK:
Well, this evening I "wrote" and ran my very first program on the thus far completed hardware. I was about to strip the 1st iteration of the main board of the computers master control unit of it components as I have since improved the design and will be re-building it, but before doing that I patched it to one of my completed integrator chassis' and ran a simple physics problem. Here it (the master control unit card) is, patched to the integrator chassis:



You can't do a lot of simulation with just a panel of integrators, but one well known physics problem that can be solved is the falling body problem. It only required two integrators:



Here is a rather crappy video of the program being run. The simulation solves y and the computer is operating the the repetitive mode. The horizontal axis is t and the vertical axis is y. The control unit furnishes the re-trace blanking signal and the horizontal sweep of t (the independent variable) for the oscilloscope.

Note that this isn't a plot of the bodies trajectory but the distance that it has fallen during time t. To make the program a little more exciting I added a negative initial condition value for y, instead of starting at zero velocity. The I.C. value is negative, so the very start of the solution is a plot of distance climbed, rather than fallen.

I started recording the simulation with the constant for gravity (g) at zero, so the initial solution for y is just a linear ascent straight up into outer space. However as I manually wind the constant for gravity up from zero, the ascent is eventually overcome and the body begins to fall at an accelerating rate.



Incidentally, here is what the finished master control unit will look like when finished. I am working on this chassis now, with a degree of priority, because with the completed master control unit handy I'll be able to actually start running some serious programs as I slowly complete each successive chassis of analogue computational units. 

GK:

--- Quote from: GK on June 13, 2013, 12:56:08 pm ---...................Also got my front panel for the display unit from Front Panel Express. Things are slowly progressing.........

--- End quote ---


Can't believe that almost 3 years has passed. I've had the front panel taking up shelf space since and the CRT has been sitting on a towel on the floor just waiting to be accidentally tripped or knocked over. It's finally time to get this thing finished and mounted into the computer systems relay rack, out of the way.

I ended up getting a little more adventurous with the design. I originally had a low-voltage, high current current-sense feedback amplifier for driving what was originally the horizontal coil of the CRTs yoke, and a high-voltage current-sense feedback amplifier for driving what was originally the vertical deflection coil.

The H coil has 2mH inductance and the V coil was comprised of two individual windings of 70mH each which were originally connected in series for 140mH. I had connected them in parallel for a much more manageable 35mH. Well it doesn't need to be said that the comparative bandwidth of the 35mH channel was crap. The small signal bandwidth was only 5kHz, while I had eventually gotten the 2mH axis close to 100kHz.

Well today I fixed that problem. Here is the disassembled yoke still retaining the 2mH (horizontal) deflection coil in the inside:




Here is the new vertical coil after I re-wound it. Each ferrite core half was originally wound with several hundred turns of thin copper wire to give the original 70mH per winding. Now there is 52 turns of much heavier enameled copper wire returning only 325uH per winding.



The yoke re-fitted to the CRT. I am still using the donor televisions old motherboard to supply the operating supply voltages for the CRT. Haven't progressed with this project to the extent of designing my own switched-mode supply yet.   



Here is the system up and running (my "Sprott Systems" analog computer [case M] providing the deflection signals). The current-sense feedback deflection coil driver amplifiers are those thingos sitting in front of the CRT. The originally high-voltage one has now been heavily modified to run on the same low-voltage power supply rails as the other amplifier. Performance is now awesome and more than adequate for repetitive analog computer stuff. Small-signal bandwidths for both X and Y deflection channels are currently in the order of 100 kHz, full-power (or rather full-scale deflection) bandwidths several kHz (current deliverable to the deflection coils is slew-rate limited by the maximum voltage that the linear amplifiers can swing).



This weekend I'll get the case fabrication completed.
T3sl4co1l:
Curious: any interest/ideas about a constant-intensity display?  That is, intensity ~proportional to d(x, y)/dt?

Tim
GK:
Don't think so.
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