Mini version of Scophony - its do-able

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Re: Mini version of Scophony - its do-able

Postby Harry Dalek » Tue Jan 05, 2021 6:03 pm

XP i love but sounds like it doesn't work with FREENBTV :( ,look for Free Tiny Windows 7 iso !
What steppers are you using ? bipolar ,unipolar ..hard to get the the line speed with a stepper be fine for framing mirror drum ,i used a pulley system to get the line speed when i used that idea but gave the idea up using just a DC motor no clogging...never tried the Chinese stepper drivers might be better than my go Keep working on it Watching with interest !
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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Re: Mini version of Scophony - its do-able

Postby Gregory » Fri Jan 08, 2021 7:13 am

What steppers are you using ? bipolar ,unipolar ..hard to get the the line speed with a stepper be fine for framing mirror drum ,i used a pulley system to get the line speed when i used that idea but gave the idea up using just a DC motor no clogging...never tried the Chinese stepper drivers might be better than my go Keep working on it Watching with interest !

Harry
For the frame scan motor it is a nema 22 size 1.8 degree (200 steps per rev). This is bipolar and the drive is set to divide by 8, so this gives 1600 micro steps per rev.

For the line scan motor is is a 7.5 degree (48 steps per rev). Again this is bipolar driven with divide by 8, so this gives 384 micro steps per rev.

The line scan mirror has 15 mirror faces
For 60 lines at 12.5 frames per sec the speed required is 60*12.5/15 =50 rev per sec or 3000 rpm

It was possible to reach this speed using a 20v supply for the drive and wiring up the windings in parallel. Slow ramping up is required and from what I can remember I managed to sync the motor to the signal.

The frame mirror had 8 mirror faces so
For 12.5 frames per sec the speed required is 12.5/8 = 1.5625 rev per sec or 93.75 rpm


The new line scan and frame scan electronics so far (half built)

new line frame BB.jpg
new line frame BB.jpg (42.59 KiB) Viewed 1146 times
Last edited by Gregory on Thu Jan 28, 2021 7:49 pm, edited 1 time in total.
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Re: Mini version of Scophony - its do-able

Postby Harry Dalek » Fri Jan 08, 2021 3:21 pm

Yes i recall that as well having to run the steppers up slowly to the wanted speed or if you did it to quick the motor stalls.
Happy to hear its going well in the build ,you might find you will have to adjust the laser focus for different line rates but on a small projection screen should be fine not so noticeable .
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Re: Mini version of Scophony - its do-able

Postby Gregory » Wed Jan 13, 2021 7:14 am

I have been re-thinking the electronics for driving the frame and line scan stepper motors, but I am not sure.

As steppers motors are synchronous motors, the thought is to drive these directly from the sync signals using the 4046 IC as a frequency multiplier to obtain the correct stepper frequency.

The process would consist of:

1) Initially to obtain the stepper pulses using a 4046 as a free running VCO slowly ramping up to the required speed.

2) To disconnect the output of the first 4046 and replace this with the output of a second 4046 configured to operate as a frequency multiplier of the incoming sync pulse frequency (using a frequency divider), so the output frequency would be an exact multiple frequency of the sync frequency. This should provide a very stable sync as the stepper frequency would be generated directly from the sync pulse frequency and there would not be any need for speed correction, as with a phase comparator.

The only problem is that although would be in sync, the mirror position would not neccessarily be in phase with sync signal. This could be overcome by using the mirror photo diode to initially trigger "process 2" only when the sync pulse and photo diode pulse coincide which would be at the start of the mirror scan.

Does this sound feasible?
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Re: Mini version of Scophony - its do-able

Postby Harry Dalek » Wed Jan 13, 2021 8:17 pm

Gregory wrote:I have been re-thinking the electronics for driving the frame and line scan stepper motors, but I am not sure.


Always good a rethink ,my projects at times never end as i envisioned and you never know unless you try .

A
s steppers motors are synchronous motors, the thought is to drive these directly from the sync signals using the 4046 IC as a frequency multiplier to obtain the correct stepper frequency.


Yes if you can sync the 4046 as a multiplier is a great idea as you mention below drive the line stepper up slowly those steppers are fussy at higher speeds .

The process would consist of:

1) Initially to obtain the stepper pulses using a 4046 as a free running VCO slowly ramping up to the required speed.

2) To disconnect the output of the first 4046 and replace this with the output of a second 4046 configured to operate as a frequency multiplier of the incoming sync pulse frequency (using a frequency divider), so the output frequency would be an exact multiple frequency of the sync frequency. This should provide a very stable sync as the stepper frequency would be generated directly from the sync pulse frequency and there would not be any need for speed correction, as with a phase comparator.


Interesting love to see how it go's sounds all possible

T
he only problem is that although would be in sync, the mirror position would not neccessarily be in phase with sync signal. This could be overcome by using the mirror photo diode to initially trigger "process 2" only when the sync pulse and photo diode pulse coincide which would be at the start of the mirror scan.


I used the corners of the polygon mirror as the start of the line via a opto switch it worked very well as feed back to a DC motor via a 4046 ,you really do need some form of feed back .

Does this sound feasible?


Hell yes give it go all that will happen is you will know either way i would say its worth a try ,if it works great this is the sort of hobby you have to be willing to fail to learn all you can do is try your best idea ..i will learn seeing how this go's.....all very interesting .
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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Re: Mini version of Scophony - its do-able

Postby Gregory » Sun Jan 17, 2021 8:40 am

Ok I'm going to give it a go. The main reason is that the sync loop would be totally electronic, that is the sync pulse output would control the 4046 VCO with the output going to a frequency divider, the output of which would be compared with the sync pulse. The stepper motor is only required to translate the VCO pulses to steps, so hopefully the sync should be very stable.

And here is the first problem, the sync signal for NBTV has a missing sync pulse which is used to obtain the frame pulse. For the line scan this missing sync pulse must be re-inserted as otherwise the stepper motor would not have the correct no of steps.

The only way I can think of is to delay the sync pulse by exactly one pulse duration and then add this output to the original sync pulse output, but this would mean this would be specific for one line resolution only. Ideally it would be nice to have something that would work for any line resolution between 30 and 64 lines.

If anybody has any ideas this would be most welcome.

I have an old Mac air laptop with VM ware on it, and checked the maximum frequency I can output, with audacity software. The sound card can output around 44 kHz with 96000 sample rate, so this may be OK for 60 lines.

First job is to build a sync separator with the line scan sync pulse output (without the missing pulse) and the frame scan sync pulse output. The Klass sync separator is ideal, except I need to sort out the problem with the missing pulse.
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Re: Mini version of Scophony - its do-able

Postby Steve Anderson » Sun Jan 17, 2021 2:47 pm

Here's what I did some years ago, eleven actually! These are the files I sent on to Jeremy to lay out for the newsletter format.

This has a narrower acceptance range and is centred around a 400Hz line-rate, but it may give you an idea or two...don't miss the .doc file at the end...

Steve A.

Fig 1.bmp


Fig 2.bmp


Fig 3A Colour.gif
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Fig 4A Colour.gif
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Fig 5A Colour.gif
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Fig 6.jpg
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Missing Pulse 4A.doc
(29.5 KiB) Downloaded 61 times
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Re: Mini version of Scophony - its do-able

Postby Gregory » Mon Jan 18, 2021 1:17 am

Many thanks Steve, plenty of good ideas, couple of questions

1) Does the pic need programming or as is ?

2) Is the purpose of the clamping pulse to fix the DC reference level or does it serve some other purpose?
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Re: Mini version of Scophony - its do-able

Postby Steve Anderson » Mon Jan 18, 2021 12:07 pm

Many thanks Steve, plenty of good ideas, couple of questions

1) Does the pic need programming or as is ? Yes, it will need programming, when you buy them from a supplier they're blank...or should be!

2) Is the purpose of the clamping pulse to fix the DC reference level or does it serve some other purpose? Quite correct, it's for setting a reference level/voltage.

The code would probably need an 'adjustment' to suit your line/frame rates if different to the usual NBTVA standards...and/or a different number of lines...

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Re: Mini version of Scophony - its do-able

Postby Gregory » Wed Jan 20, 2021 8:22 am

To start with I will build the line sync separator as below. This is basically the NBTV sync separator described in the handbook, with the addition of a pre-amplifier on the input to allow sufficient gain for all input levels.

sync separator 2.jpg
sync separator 2.jpg (22.87 KiB) Viewed 1169 times

Once this is up and running, the next job is the frame sync separator, and a way of recovering the missing line pulse.

Hopefully it would be good to have this work for :

1) 32 lines, 400 hz, 12.5 frames/sec
2) 60 lines, 750 hz, 12.5 frames/sec
Last edited by Gregory on Thu Jan 28, 2021 7:45 pm, edited 2 times in total.
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Re: Mini version of Scophony - its do-able

Postby Steve Anderson » Wed Jan 20, 2021 1:36 pm

Well the 'Eureka MkI' as before does all that, less the 60-line/750Hz/12.5fps. If you need more input gain (how much?) that can be included as a couple of minor changes, the existing circuit has a gain if between 1 and 3 (VR101). No need to build any of the circuit above.

To add 60/750/12.5 would probably require a change of micro to a 14-pin device (a PIC16F688 or PIC16F684, with extra pin(s) to select which standard) but the vast majority of the rest would be unchanged...and a fairly simple update to the code.

The only additional thing I would need to know is the nominal width of the line-sync pulses at 750Hz.

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Re: Mini version of Scophony - its do-able

Postby smeezekitty » Wed Jan 20, 2021 2:27 pm

Steve Anderson wrote:Well the 'Eureka MkI' as before does all that, less the 60-line/750Hz/12.5fps. If you need more input gain (how much?) that can be included as a couple of minor changes, the existing circuit has a gain if between 1 and 3 (VR101). No need to build any of the circuit above.

To add 60/750/12.5 would probably require a change of micro to a 14-pin device (a PIC16F688 or PIC16F684, with extra pin(s) to select which standard) but the vast majority of the rest would be unchanged...and a fairly simple update to the code.

The only additional thing I would need to know is the nominal width of the line-sync pulses at 750Hz.

Steve A.

Detecting the line rate and sync pulse width is certainly doable though.
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Re: Mini version of Scophony - its do-able

Postby Steve Anderson » Wed Jan 20, 2021 2:40 pm

smeezekitty wrote:Detecting the line rate and sync pulse width is certainly doable though.

That it is! However, I considered sources (mainly discs) spinning up and down may cause a 'jump' in modes. Plus with the now additional spare pins on the micro more than just two standards could be accommodated. This may, or may not cause the auto-detect to become confused. There's only one way to find out!

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Re: Mini version of Scophony - its do-able

Postby Gregory » Sun Jan 24, 2021 10:15 am

I am now half way through building the sync separator - unfortunately not too much time to spare the last week, hopefully should finish this the coming week.

Also thinking ahead about the missing pulse problem, as Steve pointed out detecting this produces a delay which is too late, so it requires to know in advance where to place the pulse.

The solution of using a PIC is an excellent solution, but perhaps I can cheat using a cmos 4001 IC (if it works) although
this would have the disadvantage that it would not automatically adjust to the 32 or 60 line, but there would be a switch to manually select this. If necessary further formats could be accomodated with additional switching and minimal extra components.

The way I thought is that if for each line scan pulse we produce a delayed pulse signal, which would be the same pulse width as the original line scan pulse but delayed by exactly one line scan interval. This delayed signal and the original line scan signal would go to the two inputs of an OR gate or equivalent circuit, and the output should produce a line can signal with no missing pulse.
Last edited by Gregory on Thu Jan 28, 2021 7:44 pm, edited 1 time in total.
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Re: Mini version of Scophony - its do-able

Postby Harry Dalek » Sun Jan 24, 2021 12:19 pm

Hi Gregory i could do it with one half of a 4528 funny enough i was just looking at the circuit again to draw it up i can show you a scope image if you look later .
Here i used it on passive modulation idea for a old oscilloscope
viewtopic.php?f=15&t=2641&hilit=passive+modulation

ON the page i can see i was looking at using Steve's circuit as well but went with a simpler idea i was experimenting ...( i was also looking at using framing missing pulse for FSC thats the 3rd little board switching the video via a 4066 and 4017 set to count to 3 r g b ) Steve's circuit would work too and good to very happy with 32 48 line and 60 takes a little to fall back into frame when a loop video is used at higher line rate when video repeats mine as well didn't really need adjusting i used it up to 120 line low band width video ,there it gave a slow roll drift videos on that page Vampira lady .

So there's lots of ways to do it just up to you if you want to use your own idea or copy .
i will post up a scope image below
Attachments
P1070620.JPG
P1070624.JPG
P1070622.JPG
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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