Flying Spot Scanner Construction Journal

A build of a 32 line flying spot scanner.

Moderators: Steve Anderson, Dave Moll, Andrew Davie

Postby Lawnboy » Thu Apr 04, 2013 8:19 am

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....


Yes, Steve I do plan on replacing the lamp with an ultra bight led eventually, but I would like to get it working with the original incandescent lamp first. Call me a purist :D.

BTW Steve I like your new avatar (magic eye tubes for those reading this in the future.)
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Postby Steve Anderson » Thu Apr 04, 2013 4:51 pm

Lawnboy wrote:BTW Steve I like your new avatar (magic eye tubes for those reading this in the future.)

Here's the original. It was meant for a NBTVA newsletter article that I never got around to finishing, hence the "Photo 1" title.

Steve A.
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Postby Lawnboy » Sun Apr 14, 2013 3:57 pm

I spent quite a bit of time this week working on the scanner. It now has a base, and stilts for the projector. The disc has also been painted and mounted on its VCR head drum hub. I was lucky to avoid having to turn the hub down on a lathe by popping off the drum and reversing it, exposing some threaded holes on the underside. I am concerned with how to drive the disc. I bought the 0.5mm stainless steel version, so it is a bit heavier than the aluminum discs I usually work with. I’ve never had good luck driving larger discs and could only get my last one to run using more than one motor. Has anyone used the larger motor from the club yet?

The power supply is the next step. I have an 18v laptop switching p/s to power the circuits and motor. I’m also looking into getting the 34v at 1.5 amps for the 50w led that will eventually replace the incandescent lamp. Is there a voltage regulator that can handle that or should I go for a ready built power supply?
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The glue is just holding up the disc mount. Haven't screwed it down yet.
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Postby Steve Anderson » Sun Apr 14, 2013 6:04 pm

Lawnboy wrote:I’m also looking into getting the 34v at 1.5 amps for the 50w led that will eventually replace the incandescent lamp. Is there a voltage regulator that can handle that or should I go for a ready built power supply?


A LM317 will just about handle that but I would suggest an external series pass transistor to do the bulk of the work. Depending on the raw DC voltage into this will dictate the size of the heatsink you may need...I'll do a little research...

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Postby Harry Dalek » Mon Apr 15, 2013 12:22 am

I used the lm317 s big brother the lm350 3A 1.5 to 33 volts adjustable for my mirror drums flat car fan motor worked very well didn't even get warm as i recall and just hook it up as like its little brother.
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Postby Lawnboy » Mon Apr 15, 2013 8:40 am

Harry- I thought about using a LM317 or LM350 but if I use a transformer and filter caps the voltage is likely to go higher than 37 volts with no load.

Actually I just looked online and they do sell the 50W leds along with the driver for it, and its still pretty cheap. It looks like a switch type p/s. That may be the way to go since I haven't had much luck finding a reasonably sized and priced transformer. Do switching supplies cope well with PWM modulation?
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Postby Steve Anderson » Mon Apr 15, 2013 12:43 pm

Lawnboy wrote:...Do switching supplies cope well with PWM modulation?

Shouldn't be a problem as long as the load is within the supply's rating plus a bit of filtering (a reasonable sized capacitor, but not huge).

On the subject of the LM317/350 etc...it's only the input to output differential that sets the limit. The maximum across the device is (say) 37V, but the actual output voltage can be anything. I use a LM317 in my audio pre-amp, input volts is nominally 350V, output is 330V...obviously it's tube/valve...

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Postby Steve Anderson » Mon Apr 15, 2013 1:13 pm

Lawnboy wrote:...since I haven't had much luck finding a reasonably sized and priced transformer...

Don't forget you can always use two lower voltage transformers in series. Two 18V trannies will be a nominal 36V, x 1.414 = about 51V, somewhat more off-load.

Or a 12V and 18V in series, 30V x 1.414 = approx. 43V.

Make sure you get the phasing correct though...

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Postby Lawnboy » Tue Apr 16, 2013 2:26 pm

Screwed down the disc mount today and did a test run of the projector and disc, then hit my first major snag. I failed to remember that the lens reverses the apparent orientation of the disc, so the curvature of the lines is reversed. I will have to backtrack and do some rebuilding. The toughest part will be to modify the projector again, since I will have to replace what I had cut out for the disc on that side, then cut out that same area on the other side. Or I could cut the other side off as well and make a new set of mounts for the front half of the projector. I will decide tomorrow.

Also here's another pic with the disc in place. It's starting to look like a real scanner now.

Update: What I will probably do is add a mirror in front of the objective lens to reflect the raster 45 degrees. That will fix the raster orientation and if it has an adjustable mount (like a motorcycle mirror) it will also help with focusing.
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Postby Harry Dalek » Wed Apr 17, 2013 12:44 pm

Lawnboy wrote:Screwed down the disc mount today and did a test run of the projector and disc, then hit my first major snag. I failed to remember that the lens reverses the apparent orientation of the disc, so the curvature of the lines is reversed. I will have to backtrack and do some rebuilding. The toughest part will be to modify the projector again, since I will have to replace what I had cut out for the disc on that side, then cut out that same area on the other side. Or I could cut the other side off as well and make a new set of mounts for the front half of the projector. I will decide tomorrow.


It might be an idea to try and reverse the motor direction and swap the disk around back to front ? it would save a lot of work i think i had this problem as well and you can invert the video if need be via your electronics if thats a problem in time ..
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Postby Lawnboy » Thu Apr 18, 2013 7:33 am

Harry the problem isn't the scanning direction of the spot, its the curvature of the lines. The projected raster is curved as if you were viewing it from the left side of the disc, not the right. It would still work but there would be excessive curvature on the final image. Actually I'm growing to like the idea of the mirror, since it will be easier to aim the beam, rather than shoving books underneath the machine to raise or lower it.
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Postby Harry Dalek » Thu Apr 18, 2013 10:40 am

Lawnboy wrote:Harry the problem isn't the scanning direction of the spot, its the curvature of the lines. The projected raster is curved as if you were viewing it from the left side of the disc, not the right. It would still work but there would be excessive curvature on the final image. Actually I'm growing to like the idea of the mirror, since it will be easier to aim the beam, rather than shoving books underneath the machine to raise or lower it.


I used a video camera lens i don't recall this problem all FPS used projectors so any one else have this problem ?
Still sounds like you have worked it out good luck i am enjoying viewing the build.
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Postby Lawnboy » Thu Apr 25, 2013 9:38 pm

Nothing new with the build yet. I had a busy week and probably won't get to back to working on the scanner until next weekend. I am starting to think about the electronics though. I would like to use the same photodiode in the sync opto fork to trigger both the motor control circuit and the sync inserter. Would that be possible? The sync inserter is in Vol 35 No. 1 and the motor circuit is in Vol 34 No. 1.
I also ordered the 50w led and power supply. I won’t be in until next month since it is coming directly from China. I was thinking, since the led is a “cool white” (in other words, borderline blue), would the club's dome sensor in the head amp be able to pick it up when the scanner is used in flying spot mode? I know there is very little red in the spectrum and probably almost no IR, so this may limit its usefulness as both a scanner and a monitor unless I use a PMT. I remember that Steve A mentioned somewhere about using a blue sensitive version of a BPW34 but I don't know if that will have enough surface area to compete with the dome sensor, unless I use an array of them if that is even possible.
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Postby Harry Dalek » Thu Apr 25, 2013 11:20 pm

Hi if you are trying to do what Troy is and where i was that sync pulse needs adjusting see Troys posting the Gary filter 555 timer monostable circuit between the lm311 and PLL works like a dream .
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Postby Steve Anderson » Fri Apr 26, 2013 4:19 pm

Lawnboy wrote:...I remember that Steve A mentioned somewhere about using a blue sensitive version of a BPW34 but I don't know if that will have enough surface area to compete with the dome sensor, unless I use an array of them if that is even possible.

Careful!! Blue-enhanced, maybe, but at the expense of the other longer wavelengths...in other words they have dumbed-down the sensitivity to red/green/IR etc...you simply can't defy quantum physics.

Yes, you can use several BPW34s at the same time. Simply put them in parallel, apply bias and off you go. Upside is that you get double the sensor current each time you double the number of sensors whereas the non-coherent noise only goes up by 3db per doubling...

Chris, Clint and others have done a lot in this area of weak light detection...

http://www.modulatedlight.org/

Returning to the 'dome sensor'....this is an unknown device which somehow was unearthed by the club. But little is known about it. I did try to find a matching part from a supplier as the Club Shop was running low on these. The last thing I heard was that tests were underway...that was about a year ago...

I think...but I'm not certain, the attached was what I suggested...Farnell stock number 1219006, £3.90++ (one-off).

Steve A.
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