Narrow-Bandwidth Television Association

A quick update: I just finished making a slide mechanism for fine-tuning the location of the opto fork for accurate placement of the sync pulse. The weather is starting to get really nice here and I’m finding it hard to find time for the scanner with all the yard work and the wonderful temperatures outside. Harry, could you please point me to that post with the 555 monostable?

ooh that looks very nice well done.

Re the 555 - I may have given Harry that circuit (Harry can you confirm that?) - but that was using what Harry had at hand at the time - if you are just trying to wave shape the encoder pulse then a Schmitt trigger is a better option as shown here:

http://www.taswegian.com/NBTV/forum/fil ... ol_206.jpg

Hi the 555 monostable is the..... encode-sync-motor.jpg in Troys post
http://www.taswegian.com/NBTV/forum/vie ... &start=150

Its Garys filter on that monostable the 2 10ks and 10nf you need to use along with it .

I put a led on the output of pin 3 good indicator .

I know i ran that part of the circuit off 5 volts .

Just to clarify though - that modification to the 555 circuit was to allow sub 50% mark-space ratio - again that was required because that was what Harry had at hand - there are better and simpler ways of doing it, but it works.

Thanks guys. Here are my thoughts on the sync system. I wanted to use a 4060 with the missing sync pulse as in Peter’s color bar generator, (or some other way of getting a missing sync pulse) then use a 555 monostable triggered by the 4060 to create the sync pulses of the proper width to feed to Peter’s universal clamp and sync inserter, negating the need for the second phototransistor on the opto fork. This way as long as the disc is properly synced up everything should be where its supposed to be. I don’t know if the sync holes on the disc are the correct size for triggering the sync pulse, but I guess it doesn’t matter much as long as they are in the right spot in the line. I also want to run an led off of the 555 to act as a timing strobe to ensure the disc is not a line or two off. I will paint a reflective marker on the back of the disc.

Or, I could try using the same phototrans for both the speed controller and the sync inserter (if that’s possible) and ditch the 4060 missing sync system.

Or, I could skip everything altogether and just feed the output of the 4060 or whatnot to the monitor’s speed controller. Gary, would your software be able to read a square wave sync pulse on the sound channel?

Thanks Harry- I knew it was in there somewhere! I will catch up on that thread when I have a few minutes.

No TBP doesn't handle sync on right channel (unless the video is there too) except for some esoteric colour formats. BUT, if your signal is xtal locked (400Hz) then you don't need the sync at all for TBP to display a picture - simply use the line and frame controls to frame the picture and it will stay temporally locked to the xtal frequency.

Again I would just like to point out that the 555 trick Harry has used was just because that was what he had at hand - if starting from scratch it would be a better idea to use, say, CD4528BC monostable as Klaas used in his sync separator - no shenanigans then needed.

This weekend I wasted most of my NBTV time trying to decide if I should overhaul my plan for the electronics. I was leaning towards an idea I had a few years ago that involved putting most of the electronics in a separate controller/NBTV video mixer. The controller would have a sync generator, accept and mix the signal from the photocell head amp(s) and insert the sync pulse. The aim of that project was to use the controller in conjunction with a mirror drum scanner (yet to be built) and a disc-based scanner like this one to simulate Baird’s studio at the BBC in 1935. He could fade between his caption scanner, the multiple photocells from the studio mirror drum and also fade to white.
However I decided to keep the electronics in the scanner for now, and eventually move them to a separate controller unit. What made things complicated was that the scanner I am building now (and very likely the laser-based mirror drum that is yet to be built) will also be able to act as a monitor as well, so the controller would have to have provisions to feed video as well as receive it. Add in the possibility of RGB color on either scanner and the headache of gamma correction in both directions and it wasn’t worth starting to build something that is really a project in itself.

One thing I did complete was the Triple Waveform Generator that had been sitting in a box unfinished for about 2 years. I wanted to see if I could pull the sync pulse from it to drive the motor controller, but it was in the form of a “black burst”, and I need a clean 32-1 positive-going sync pulse to take the place of the opto fork on the sync inserter. I will use the sync from the color bar generator instead. The next step is working a bit more on the cabinet.

The 50W led arrived this weekend! It’s a lot bigger than I thought, and the active area is almost twice the filament size in the lamp. I gave it a test run, and it is indeed very bright. It puts ordinary luxeons to shame. I happen to have a heat sink that fits perfectly inside the lamp housing, and already mounted the led to it and tried it in the projector. It’s not as bright as the original lamp, but should be adequate for a picture of at least a few square inches. I only ran it long enough to snap a few pics until I can get the fan wired in. Should be fun trying to modulate it!

I also replaced the base board with a stronger, thicker piece of plywood. The original base was slightly warped and I didn’t want to fool around with it later.

I also found an adjustable motorcycle mirror to steer the beam. I ordered a first-surface mirror to replace what’s left of the original mirror, and will have that cut to size soon.

Great progress Lawnboy.

Pity about the 'dead cat'.
Should have shielded the Luxeon.

I jest of course.

I'm following this thread with interest.

Kind regards,

Graham

Woh man...That LED is a MONSTER!

Graham- Yes, I figured someone would get a laugh from my cat Cowboy sleeping amongst the mess that is my apartment right now.

I’ve already determined that the heat sink I had for the led is not going to cut it, so luckily I had another heat sink of the same style with larger fins that I cut down to size. It brings the led a little closer to the lens and out of the plane of the original filament, but that shouldn't matter much.

Well after more than 6 months of inactivity on this project (and NBTV in general) I am finally back on it, hopefully to completion this time. I have actually been working on it every now and then for the last month or so and got a lot done on it since my last update. The case has been put together, the motor mounted and the motor control circuit built and tested. The next step is wiring up the switches and hoping it works as well in reality as it does on paper. I should have that done by the end of the weekend if everything goes to plan. I will post pictures as soon as the sun comes up again.

Success! I spent a good few hours wiring the whole thing up and it actually worked on the first try! I am not used to that. Here are a few pictures of the device in its new case.
The switches are (from left to right), main power (upper fan on), motor, and lamp (projector fan on). The fourth hole will switch between the incandescent lamp and the LED, but that will come later.
The shaft below that is a 2P6T, which routes the signals from the triple waveform generator to the sync separator and motor controller and also allows for an external video/timing signal from the RCA jack to drive the circuitry.
I have also added a simple timing LED to show when the disc is in sync because it is hard to hear the motor over the fans. Right now it is connected to the output of the sync separator so it flashes at every sync pulse, but I would like to eventually get it to flash once per frame at the missing sync for proper framing, but that sounds like it could be difficult without additional complex circuitry.
Note: The image of the raster was taken without the mirror or the disc mask in place.

Hi lawnboy i was just wondering how this was going and you have posted !
Looks very workable ,have you worked on the light detection side ...big solar cells work well.\
To test move the cell array to and from the reflected scanned area ,i found it like DXing with light at close distances signal fading in the snow with distance yours might be easier using more light than my one led luxeon .
Best to use large shapes letters for your test card Gary was sure right pointing me in this direction .

It's been a bit of a frustrating week. I started making the disc mask to replace the one I was using for testing purposes (just a piece of cardboard with a square hole in it), and noticed that something was a little off. Turns out that the disc is about a quarter of an inch too far in so the raster is not in the center of the projector gate. Earlier in the project I replaced the base with a thicker, more sturdy piece of wood and transferred the measurements and screw holes over directly, but apparently something went wrong. The projector was designed to take full-size slides so the gate is large enough to handle the miscalculation without shading any of the holes, but the raster comes out of the lens a bit crooked and misses part of the mirror. I will try to reposition it this weekend.