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| Home Brew Analog Computer System |
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| GK:
--- Quote from: GK on July 17, 2013, 02:52:09 am --- --- Quote from: Jebnor on July 17, 2013, 02:14:04 am ---2) drill with a small hole (2mm) or with a center Drill that can be purchased at any machine tools shop. --- End quote --- You mean: ? Used them many times in the tailstock on the lathe but never in a drill press. Instead of using one to drill a small diameter pilot hole (the larger twist drill will still walk to a degree), how about using a larger diameter one to drill the hole in its entirety? --- End quote --- Here is how the panel drilling has worked out using a 5/16 center drill for the 4mm banana sockets. 120 holes drilled so far, a couple of thousand more to go.......... If one looks really closely some wonkyness can be perceived in the hole positions, but it's about as good as I think I should expect for a manual drill-press job. These are the front/patch panels for the computers 30 integrators. The drilling template(s) are generated in Protel, printed and then sticky taped to the blank panels. After that it's just a tedious process of center punching and then drilling. Panels are 3mm thick, 19" relay rack by Hammond. |
| GK:
--- Quote ---Quote from: GK on November 26, 2013, 07:10:44 PM The harmonic generator will simply consist of a 5-stage binary ripple counter to produce the fundamental and harmonic frequency components. The sine fundamental and harmonic functions are produced by filtering the squarewaves with simple resistance-tuned multiple-feedback bandpass filters and the -cosine terms for each sine function are produced by simple resistance-tuned all-pass filters acting as unity gain 90 degree phase shifters. Not stuffing around with crusty inductors or trimmer capacitors here. Unlike in the 1958 design paper with its "shock-excited" resonant circuits, oscillation will be continuous with the gating and sequencing pulses/control signals derived appropriately from the harmonic generator clock source and ripple counters. --- End quote --- Well that was a bit of an oversimplification. To generate the fundamental (20 kHz) and the 2nd through to the 5th harmonic reference frequencies something a little more complicated than a 5-stage ripple counter was of course required due to the non-integer division. Here is the circuit I knocked up on breadboard this afternoon to do the job, out of parts I had at hand. The fundamental and the 2nd, 4th and 5th harmonics are all derived from an 8MHz master clock by digital division. The fundamental, 2nd and 4th harmonic are generated by three stages of ripple counting while the 5th harmonic comes from a separate free-running divider (IC2) locked into synchronization by the 20kHz fundamental waveform. The trickiest part was the 3rd harmonic (60kHz), which cannot be derived from the 8MHz master clock by integer division (8M/60k = 133.33). It is no good generating the 3rd harmonic from a separate master clock (say 6MHz) as it then won't be phase coherent with the fundamental. The 3rd harmonic is generated by a PLL acting as a x3 multiplier, using the fundamental as a reference. All generated signals have the necessary locked-in phase relationships, as all harmonics have a coincident negative going transition with the fundamental. Now I just have to knock up the tuned MFB filters that will turn the squarewaves into sinewaves (while maintaining the phase relationships), and the all-pass filters to produce the cosine reference terms. Then it will be onto assembling the Fourier character ROM..... and then the multiplexing, addressable screen location memory and deflection logic............... Put my Type 551's "dual beams" to good use............... |
| GK:
I'm doing the final machine work to the front panels now (integrators panels only), but before I can complete the job and start assembling the individual 19" cases I have to figure out a convenient way to electrically connect (when mounted in the rack) each front panel to the other. Back in the good old days analog computers were made with big, heavy power supplies with heavy, low impedance bus bars for the ground distribution as powering racks of various analog modules from common rails inevitably meant that the signal ground and power ground return was essentially one. Big heavy bus bars for the ground with low resistance were therefore mandatory to keep interference/interaction between the modules to a minimum. I've worked around this problem by instead incorporating a separate power supply into each rack case, to power the (standardised ten) analog modules in that same case only. Each front panel will have a single star grounding point to which all the module grounds and the PSU ground terminate. Power supply ground return currents are therefore kept inside the case and no power supply ground return currents share the signal ground termination between rack cases. This means that the entire front (patch) panel acts as a low impedance signal ground plane (and to a lesser extent the equipment cases and the actual relay rack(s) itself. However I don't think that I can rely upon the mounting hardware holding each chassis into the relay rack to behave as a solid earth connection between the panel and the rack itself, thus ensuring that all (grounded) chassis panels are electrically connected together. After all the panels are painted, as is the rack, and the mounting bolts screw into (otherwise loosely fitted) cage nuts. At the moment I am considering fitting a 4mm nutsert (press fitted captive nuts) into each of the four corners of each panel, so that each chassis panel (after fitting to the rack) can be linked to the ones directly above and below it with a total of four short (a couple of cm) earth braids having a lug at each end. That will work but its probably not the most elegant solution. I am open to alternative suggestions. The design also needs to remain modular and not all chassis panels will be 3U. |
| GK:
--- Quote from: GK on November 26, 2013, 08:10:44 am ---Now I just have to knock up the tuned MFB filters that will turn the squarewaves into sinewaves (while maintaining the phase relationships), and the all-pass filters to produce the cosine reference terms. Then it will be onto assembling the Fourier character ROM..... and then the multiplexing, addressable screen location memory and deflection logic............... --- End quote --- First part done. Here are reference signals sin wt, sin 2wt, sin 3wt, sin 4wt and sin 5wt, as produced from the squarewaves by the MFB filters And here is -cos wt, -cos 2wt, -cos 3wt, -cos 4wt and -cos 5wt, as produced from the sine terms by the all-pass filters. The breadboard so far: The circuit (repeat 5 times): |
| notsob:
For your 4mm shorting - perhaps use these shorting bars - http://au.element14.com/pomona/4115/shorting-bar-for-binding-posts/dp/1538396 or this is available but I would use a bolted on link - http://www.newark.com/pomona/5145/double-banana-plug-shorting-bar/dp/94F940 |
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