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nbtv wrote:Of all the mechanical TV systems the one that intrigued me the most was the Scophony TV system. 400 lines and 24 inch screen, not bad for 1938, in fact not bad for now.
I was toying with the idea of making a small system based on the twin mirror drum system used in the Scophony, but limiting the screen size to say 6 x 8 cms with 60 lines. The purpose would not be to copy all the optics Etc of the original but use the main concept of 2 mirror drums to make a compact televisor.
A laser diode pointer could be used as the light source and avoid the lenses, as this would not need focusing if one accept a spot size of around 1mm this would give a 6 x 8 cm display for 60 lines.
First problem would be the high speed line scanner - desperately looking for a polygon mirror to do this, but nothing yet, they use these in laser printers and copiers, but most have the motor embedded on the PCB. The motor could be a hard disk motor, these run up to 15000 RPM and are synchronous, and I have many faulty hard discs.
[/quote]Any info for any parts going cheap (laser diodes, polygon mirrors Etc) would be most welcome
nbtv wrote:Harry,
Thanks for the info and the links - very useful and plenty of food for thought. I have managed to source the polygon mirrors. The ones I found are 12 sided at a very reasonable $5 each, so I ordered four of these, to have spares as well (they are only 7mm thick, so they are only suitable for the line scan). If anybody is interested the link is:
http://opticaldesignsoftware.net/prod034.htm
The frame scan mirrors I think I will have to make, as ideally I would want this 12 sided also but much thicker
nbtv wrote:Well phase 1 of the project has started - polygon mirrors have been ordered and I have now stripped down 3 HDD motors, so now I have to wait for the mirrors to come.
I have checked on the RPM of HDD motors and the standard speeds for HDD appear to be 5000, 7200, 10000, and 15000 RPM, but most, especially the slighter older ones are 7200 RPM
I don't know if the speed is limited by the motor or driver or both but I will be designing a motor driver, so should soon find out.
RPM required with a 12 sided polygon mirror would be
32 lines 12.5 frames/sec = 2000 RPM
60 lines 20 frames/sec = 6000 RPM
120 lines 25 frames/sec = 15000 RPM
Any circuits for a high performance motor driver for HDD motors would be most welcome
Gregory wrote:I have been looking further on the web into HDD motor drivers and from info available it seems to get these motors running to a high speed most use a PWM driver which monitors the back EMF to know exactly where the rotor position is.
Don't now if this is necessary but I have ordered and added to the shopping list a couple of cheap ready made drivers with PWM control to see if this can spin the motor to at least 6000 RPM.
Initially the line scan motor will be with manual speed control but at some stage it will probably be necessary to make the motor driver, as it will have to synchronise the motor to the line sync, and with ready made drivers, this may be difficult.
Also I have ordered a cheap stepper motor driver {$5} for the frame line motor. This should be ideal for driving the motor as with 3 amp rating and micro-stepping, it should provide smooth rotation, even at low revs, as this would give (200 x 16) 3200 virtual steps per revolution
Gregory wrote:Hi Harry,
Thanks for the link and a very interesting project on the camera and must have been a lot of hard work. Did you find the oscillating mirror for the frame worked well, and produced a sawtooth type movement.
Back to the line scan driver - also found that a TDA5140A Ic can be used to drive an HDD motor with very few external components.
At the moment i'm over in the UK for 14 days but hopefully when back should have all the parts come through and get going with the line scan mirror and driver. Hoping to get the mirror spinning as stable as possible so the sync signal required to lock will be minimal.
Gregory wrote:Looking for a polygon mirror for the frame scan similar to the photo below - if anyone can help or has one to sell please contact me.
Alternatively if anyone has any experience making one with accuracy - any info would be of great help, Thanks
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