by Ralph » Tue Apr 02, 2013 2:13 pm
The original goal of this particular project was to construct a Nipkow televisor (my first, if you ignore the trivial task of assembling a MUTR "kit") that would provide a realistic appreciation of the trials, tribulations, and occasional triumphs of those late 20's and early 30's experimenters building basic equipment with manual speed control. There is no doubt that, with the addition of the simple "string braking" system, an enthusiast could have watched and enjoyed the relatively short programming intervals of the period. Note that I said an "enthusiast"! To get spouse and family to pay attention would have required a high-end televisor with the ability to lock the display automatically.
The final steps to operational status with this project involved some simple modifications:
(1) The previous post reviewed the solution to the "diffuser problem", achieved by providing adequate space between the LED's and the diffuser material.
(2) Increasing the light intensity was a simple matter of the black set bias control of Klaas's one transistor LED driver. I had set the potentiometer to the excitation point of the LED's while observing the LED cluster directly. In fact, the proper way to do it is with the diffuser in place and the the disc running. If the black level is set that way, there is a lot more light available with normal video drive.
(3) With a bit of experience, the simple string braking system for framing and phasing is so effective that it is possible to take longer exposures, providing better photographs of the display. The image below shows an earlier image of my friend Bugs Bunny (A) - great focus, but with mottling as a result of the diffuser issue and barely adequate light for the single-frame photograph - 1/12.5th of a second. (B) shows the current situation with the new diffuser arrangement, a brighter image as a result of the bias change, and a 1/2.5-sec. multi-frame exposure (an even 5-frames).
Although the unit is now operational, the inside of the light-box is far from elegant, with PC-board pieces from two earlier iterations lashed together in a distressingly informal way! By the end of this week what will probably be the last contribution to this thread will be a new integrated pcb for which I will provide documentation and board-layout data.
Ralph
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