Electronics > Projects, Designs, and Technical Stuff
Home Brew Analog Computer System
AlfBaz:
Hi GK great thread, I also follow your work with great interest.
On the subject of front panels, have you considered laser cutting services? I was just looking and found quite a few that were reasonable, especially if you can get away with plastic. If shielding is an issue it may still be more viable to simply line the inside of a plastic panel with foil. Given that they can not only cut holes of whatever shape but may also be able to do 2 tone legend engraving
Just a thought
GK:
--- Quote from: woodchips on July 21, 2013, 10:23:25 pm ---Just seen this post on tekscopes about capacitor probems etc.
http://www.maximintegrated.com/app-notes/index.mvp/id/5663
--- End quote ---
Dunno if anyone is going to get stroppy over copyright on these old texts, but here is a bit on capacitor leakage and dielectric absorption from Computer Handbook Huskey & Korn, and Electronic Analog and Hybrid Computers, Korn & Korn. Numerous other ancient texts cover the same ground too.
I'm sorry to say it but Bob Pease was a little late to the party on this one.
GK:
--- Quote from: AlfBaz on July 22, 2013, 02:12:41 am ---Hi GK great thread, I also follow your work with great interest.
On the subject of front panels, have you considered laser cutting services? I was just looking and found quite a few that were reasonable, especially if you can get away with plastic. If shielding is an issue it may still be more viable to simply line the inside of a plastic panel with foil. Given that they can not only cut holes of whatever shape but may also be able to do 2 tone legend engraving
Just a thought
--- End quote ---
Thanks, but I'm not sure that plastic would be strong enough; especially so to support the weight of each "modular" chassis. Another thing is that the entire composite rack system front panel serves as a ground plane for my signal ground.
GK:
--- Quote from: GK on July 07, 2013, 02:40:28 pm ---Well, finally, here is the Lorenz Attractor in 3-D projection with variable angles of rotation (the 3-D projection unit in action). I have to say that I am quite happy with the way the synthesized sine/cosine potentiometers worked out with the 8-bit digital pots and the sine/cosine look up table. The 1 degree step resolution and 8-bit accuracy gives a fluid variation in display that is, for all sakes and purposes, totally analog as far as I as the operator can discern. In all honesty the Lorenz Attractor probably isn't the best 3-D "object" to demonstrate the operation of the projection unit, as it is a bit complex and an interpretation of the display isn't intuitively obvious as it is with simpler shapes and objects, such as the assorted springs I posted screen photos of a few posts previously.
Here is a simplified schematic of the initial, prototype projection unit. It is based on the basic 3-D projection principle outlined in chapter 9 (Multi-Dimensional Displays) of Analog Computing At Ultra High Speed, D M.MacKay, M E. Fischer.
--- End quote ---
I have made a significant improvement to the above described 3D projection unit. The unit as shown above is only capable of rotating the projection on both the X and Y axes over the range of 0 to 90 degrees. This is quite adequate an adjustable range for graphs and shapes in isometric projection, which are typically shown at a "perspective" of 45 degrees. However I figured that it would be a lot cooler if the projection unit could in fact spin the projected display on either axis the full 360 degrees.
The reason the design detailed above is limited to 0-to-90 degree range is that the digital pots connected as potential dividers (to implement the necessary sine and cosine multiplications) can only effectively multiply in two quadrants (the positive ones) as the range of multiplication of the applied input signal is limited to the range of 0 to 1. Now while 2 quadrants of operation for either a sine or cosine function on its own represents a 180 degree range of rotation, the range is in fact limited 90 degrees when a sine/cosine complement is generated as only a 90 degrees of variation is achievable before one function hits its limit at the point of transition into an off-limits negative quadrant.
However I figured out a simple way to achieve the full 4-quadrant range of operation with each digital pot, thus eliminating the above described restriction and permitting a full 360 degree range of variable rotation on each axis. It's quite simple really. I just followed each of the 8 digital pots implementing the sine and cosine multiplication functions with an individual "amplifier" having a gain of either 1 or -1, depending on the state of a logic control input. The range of multiplication is thus extended from 1 to 0, to 1 to -1, simply by asserting the logic control line to switch the amplifier from a gain of 1 to -1 whenever operation in the negative quadrants are required.
Here is a video of the resultant prototype in action. At the moment the angles of rotation are not manually variable/settable as they were previously as I haven't gotten that far with the code yet. I just wrote a test subroutine to linearly and continuously rotate the projected display on each axis the full 0-to-360 degrees at a fixed and steady rate (one axis rotating twice as fast at the other). Once again the "object" being displayed is the Rössler Attractor:
Cool, huh? ;D
Odysseus:
Damn right it's cool.
Give us a heads up when you try attacking the N-body problem. :-+
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