DIY Scanning Disk TV

[old_tv_nut]

Are all the pulses full amplitude and clipping at the max voltage now? That is the first important thing.

The 4046 contains more than one phase detector, connected to different output pins. The one used in all the club schematics is edge-triggered (I think positive-going edges, but I forget), so it doesn't care about the pulse width. However, it may not like pulses that rise too slowly, so plenty of signal amplitude and clipping or else a Schmidt trigger to make sure it rises quickly is the second important thing. The other nice thing about this phase detector is that it is also a frequency detector, so if the disk speed is too high or low, it will be forced back toward the correct value.

The other more common types of phase detector (including the unused ones in the 4046) are sensitive to pulse width and might like to have a 50% duty cycle on both input pulses, depending on the design. They also have only a weak frequency-offset response, so the speed has to be within a certain "pull-in" range to start with.

Can you post a picture of the oscilloscope trace of your optical pulses?

[yagosaga]

The development of color on the Nipkow disk made some progress, see:

http://www.nbtv.wyenet.co.uk/hot.htm

and

http://www.copycoder.com/phpbb2/viewtopic.php?p=126#126

(Mickey Mouse on the Nipkow disk in color.)

My own mechanical TV set is disassembled now. With a little help from my friends it will get a new and professional looking wooden house.

[mbates14]

im still havin the problem where the whites are washed out, and darks are way too dark, you cant see them.


Im wondering if its because I used lm741 with single supply voltage. Dunno.

Anyway, that picture of the kids face you have on your site, looks like a ghost head. thats how bad it is.

[old_tv_nut]

Can you post the diagram of your video output circuit including the LEDs? If the whites are bright enough but clipped, you probably have too little resistance in the FET source circuit and/or too many LEDs in series in the drain circuit. (???) If you could measure the voltage swing at source and drain with a scopoe, that would help diagnose it.

[mbates14]

im only using 3 in parallel, but one bleedoff resistor.

the signal does not look clipped on the scope. But at the point where its not clipped, I can barely see it. Im using 15,000mcd leds.


But when I turn it up to start to really see it, it begins to clip, and can see it clearly on teh scope. But, when I lower it out of clipping, the scope cant trigger it.