Flying Spot Scanner Construction Journal

A build of a 32 line flying spot scanner.

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Flying Spot Scanner Construction Journal

Postby Lawnboy » Mon Apr 01, 2013 12:52 pm

As some of you know from my previous post on leds, I am currently building a 32 line flying spot scanner. So I might as well start a construction thread about it.
Some work has been done already, so here is a brief catch-up description.
I am using an Argus 300 slide projector, which has a 300w lamp and forced-air cooling. The slide mechanism has already been removed and a slot cut out of the side for the disc. I am using the new 15” disc from club sales, as a 12” disc is too small and the 19” disc previously available from the club scans an area bigger than the projector’s slide aperture. The fan blades originally were too big and would have interfered with the disc, so I found a smaller set of blades from an induction motor taken from a reel-to-reel tape recorder. I am also adding a second mains-powered “muffin” fan and a snorkel to help move air out of the box that will be built around it.
The disc will be driven with a belt and pulley arrangement and controlled by the club motor controller. A timebase generator using a 4060 will provide the sync signal. I could have used a 555 timer, but decided that the 4060 circuit from Peter Smith’s Color Bar Generator would have an advantage by already producing the suppressed sync pulse for framing. At this point the video and sync signals will be separate, but the option of combining the two into composite video may be added later using the Universal Sync Inserter in Vol. 35 No. 1.
The video pickup will be completely separate from the scanner, probably mounted in a soup can on a tripod along with a battery. I plan on using the club’s dome sensor and the new head amp circuit.
Attachments
1 Projector.JPG
1 Projector.JPG (100.71 KiB) Viewed 9570 times
2 Projector top.JPG
2 Projector top.JPG (95.16 KiB) Viewed 9570 times
3 Projector bottom.JPG
Projector bottom with the new fan blades.
3 Projector bottom.JPG (96.57 KiB) Viewed 9570 times
4 slide aperture.JPG
The disc scanning area relative to the slide projector mask.
4 slide aperture.JPG (83.18 KiB) Viewed 9570 times
5 Snorkel.JPG
The "snorkel" with the muffin fan.
5 Snorkel.JPG (91.77 KiB) Viewed 9570 times
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Postby Viewmaster » Mon Apr 01, 2013 6:21 pm

I know very little about flying spot scanners as the following might illustrate !
But if you are going to run the proj lamp from the AC mains will that not modulate your light sensor pick up with 60 Hz ? Maybe it's DC anyway??
Just a thought.
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Postby gary » Mon Apr 01, 2013 6:43 pm

Indeed it will Albert, but it's not just FSS that suffer from that - all cameras have that problem if the light reflected from subject is mains derived.

There are ways around it - see Graham's camera schematics for a nifty nulling arrangement.

Personally I just notch filter it out in software.

Ultimately an FSS is useful in that the supply to the lamp can be DC driven - theoretically all you need is a couple of mains rated diodes and a filtering capacitor - alas the (relatively) high current involved would require a pretty hefty (read expensive) filtering capacitor off the top of my head. Has anyone actually tried that? I wonder how the lamp would react to the higher (x1.4 voltage)? Eeeek. Voltage regulation starts to get a bit pricey methinks.
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Postby Viewmaster » Mon Apr 01, 2013 7:05 pm

gary wrote:There are ways around it - see Graham's camera schematics for a nifty nulling arrangement.

.

I haven't seen that nulling.....any link please.

But one might raise and lower the gain from the light sensor in sync with the AC supply as the volts rises and falls?
Raise the gain when the AC voltage is low and lower the gain when at full volts.
Any good?
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Postby gary » Mon Apr 01, 2013 7:36 pm

Viewmaster wrote:I haven't seen that nulling.....any link please.


V24 #1
I think Graham posted it on this site somewhere relatively recently, you could do a search on his posts.

I think also he is in the process of making mods to the arrangement of his camera although I am not sure if that included his nulling arrangement.

Viewmaster wrote: But one might raise and lower the gain from the light sensor in sync with the AC supply as the volts rises and falls?
Raise the gain when the AC voltage is low and lower the gain when at full volts.
Any good?


Well that's is more or less how it works but it is synced to the mains the same way the camera is - via a light sensor - that way the hum has the characteristics of the light source - don't forget for an incandescent lamp it will be twice the frequency of the mains plus include whatever thermal lag there is.
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Postby gary » Mon Apr 01, 2013 7:45 pm

Perfecting an NBTV system is like trying to slam a revolving door...
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Postby Steve Anderson » Mon Apr 01, 2013 8:36 pm

I'm not sure what is being proposed as a photo-sensor here, but whatever it is wouldn't it be be better to spectrally match the light source to the sensor(s).

If using one (or more) PMTs then blue would make sense, if using silicon then IR even better. and you wont see the flickering scan. Of course they all have their trade-offs on skin rendition tones. Something panchromatic would be ideal...ho hum...

Consider more than one sensor as with just a single sensor it will look like a flash photo with sharp and deep shadows...and you get get noise reduction thrown into the bargain. Where the signal doubles in amplitude but the uncorrelated noise only goes up by 3db. You will be battling with noise on this....

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Postby Harry Dalek » Mon Apr 01, 2013 9:51 pm

Good work looks like that projector gets pretty hot !

I found having a large light sensitive surface area to capture the reflected light off an object was far easier for me than a the dome sensor which had hot spots at best with my low light try ,might be fine for the amount of light your using but i still think if you swapped the dome sensor for the a small solar panel it would out do the dome sensor for one of these type cameras as you want a light receiver that receives light reflected back from from an object and received on a large area which is so much easier with a solar panel no extra optics needed at all.

The receiver distance from the object being filmed is a factor to as to how good the received signal is so i would go close as and work your way back to see ...i found it a bit like DXing at close distances !

And it has to be in an electronics free zone no tvs on no fluro lights near by , head amp does not like these at all all just amplified noise .

good luck
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Postby Lawnboy » Tue Apr 02, 2013 5:42 am

That is actually one thing I forgot to mention. I hooked up a BPW34 photodiode to my oscilloscope to see how bad the lamp flicker from the AC current was, and was pleased to find that it was almost nonexistent, especially when compared to a neon nightlight. I’m sure the 60hz AC frequency helps, but I wont know for sure until I get it built.
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Postby Harry Dalek » Tue Apr 02, 2013 4:15 pm

Lawnboy wrote:That is actually one thing I forgot to mention. I hooked up a BPW34 photodiode to my oscilloscope to see how bad the lamp flicker from the AC current was, and was pleased to find that it was almost nonexistent, especially when compared to a neon nightlight. I’m sure the 60hz AC frequency helps, but I wont know for sure until I get it built.



My torch was one that could strobe the effect was via the turning nipkow raster strobe lines depending on the frequency of the strobe i would expect some form of lines showing up but perhaps your old lamp can not oscillate fast enough which would be a good thing you want a clean light with no signal on it ...
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Postby Viewmaster » Tue Apr 02, 2013 6:31 pm

gary wrote:
Viewmaster wrote:I haven't seen that nulling.....any link please.


V24 #1

Well that's is more or less how it works but it is synced to the mains the same way the camera is - via a light sensor - that way the hum has the characteristics of the light source - don't forget for an incandescent lamp it will be twice the frequency of the mains plus include whatever thermal lag there is.


Thanks for that, Gary. I see that Graham's cct takes care of any thermal lag. My idea would not have done this.
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Postby Steve Anderson » Wed Apr 03, 2013 3:21 pm

Please correct me if I'm wrong (very possible) but I thought that this device was also to do double-duty as a NBTV projector too. In which case whatever the internal light-source will be will need to be modulated when in projector mode which precludes anything incandescent or AC powered....

...over to the author to clarify matters...

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Postby gary » Wed Apr 03, 2013 5:43 pm

Oh, didn't you hear Steve? He bought that Kerr Cell off ebay on April 1st.

Seriously I was only replying to Albert's question about running the light source off mains AC (obviously a LED will be off DC possibly rectified of the mains but I am pretty sure that's not what Albert meant). As usual we are a little off topic... ;-)
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Postby AncientBrit » Wed Apr 03, 2013 5:48 pm

Yes I am working on modifying my Nipkow camera, but only around the area of clamping.
At the moment work has stopped because my garage is unheated and temps. here are near freezing.

The hum cancellation remains untouched.

Note the hum cancellation circuit works as a modulator, it's not a simple subtraction of the interfering signal.
If you inspect the video signal the amount of hum is proportional to the amount of light reflected from the subject so a dark object will need less correction than a bright object.

It works well but it's not perfect and needs adjusting if the camera is panned to a new scene.

Regards,

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Postby gary » Wed Apr 03, 2013 5:58 pm

Just as well you mentioned that Graham as I had forgotten that small nuance :roll:
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