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Dennis Feucht

Electromechanical Displays, Part 1: The Nipkow Disk

Dennis Feucht
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rahuly99
rahuly99
11/8/2015 3:54:19 AM
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Re: Electo-Optical-Mechanical display
thanks even iam working on ths electro mechanical displays

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GSKrasle
GSKrasle
10/6/2015 12:17:51 PM
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Artist
Re: Electo-Optical-Mechanical display
There were no microcontrollers in those days, except maybe the first releases of 8080 and 8008, but there's no way I would have had access; the 256 T1-3/4 LEDs just about broke me.

In retrospect, it's obvious that the project was just a display, and should have been buffered from the data source, in that case an 8-bit ADC. But memory was also expensive, and eight 1kx1 SRAMS to hold four "frames" would have been pretty daunting. I guess I was ahead of my time. 

Nowadays, the same POV scheme could still work to multiply the resolution of the available LEDs, but each 'little circle' would have a much larger number of virtual pixel points defined than four. Its operation can be visualized as an array of holes (instead of LEDs) jiggling in front of a high-resolution screen. 'Not really practical, but then is a propeller-clock?

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D Feucht
D Feucht
10/5/2015 8:39:27 PM
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Re: Electo-Optical-Mechanical display
Thanks for sharing your experience with this unusual technology!

Your scheme has some of the characteristics of a Nipkow disk in its nonlinear scan. Perhaps another 8x8 array opposing the first would have balanced the rotation better. (Imbalance or runout is hard on bearings unless they are thrust bearings.) Something this nonlinear might best be driven with a uC.

"Stay tuned" for Part 2, where an improvement or two are offered along the same lines of thought.

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GSKrasle
GSKrasle
10/5/2015 1:45:39 PM
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Artist
Electo-Optical-Mechanical display
As a college freshman, I had an idea for an 'Electo-Optical-Mechanical Display' that I've never seen expressed since. I built an 8x8 array of LEDs (expensive!) attached to a bearing off-center on a spinning disk. The array was not intended to whirl like a propeller-clock, but the LEDs were intended to all simultaneously describe little circles. It was very hard to deal with getting data to it using nothing but LS TTL but it sort-of worked as an oscilloscope when I ran it with four 'frames' π/2 apart. 

The mechanics are a bit complicated: The virtual grid depends on choice of which angles of the little circle to use for 'frames', the size of the circle relative to the LED grid vertical and horizontal periods and the LED grid pattern itself (rectangles [squares?], triangles, ?). Starting with a simple square LED grid is probably not the best choice, but leaves you with a usable project even if the spinny-thing idea has to be abandoned. You end-up with unevenly-spaced rows and columns in the virtual display. I had to use dipswitches to adjust the positive and negative offsets for the π/2 and 3π/2 positions (which fed into 7483 adders). The rotary encoder triggered the ADC to maintain horizontal coherency. A counterweight is absolutely necessary for sanity (yours and your lab-mates'), and at even moderate speeds, this thing was on the verge of flying to pieces. I never figured-out a good way to mount it either; the rubber-bands at the corners didn't completely keep the array 'stable' from rotating/torquing. But it sure was a noisy, shiny attention-getter!

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