Mini version of Scophony - its do-able

Forum for discussion of narrow-bandwidth mechanical television

Moderators: Dave Moll, Andrew Davie, Steve Anderson

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.
User avatar
Harry Dalek
"Fester! Don't do that to 'Thing'"
 
Posts: 4491
Joined: Fri Sep 26, 2008 4:58 pm
Location: Australia

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)

Image
Gregory
Research Scientist
 
Posts: 49
Joined: Wed Feb 10, 2016 5:06 pm
Location: Nicosia, CYPRUS

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 .
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.
User avatar
Harry Dalek
"Fester! Don't do that to 'Thing'"
 
Posts: 4491
Joined: Fri Sep 26, 2008 4:58 pm
Location: Australia

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?
Gregory
Research Scientist
 
Posts: 49
Joined: Wed Feb 10, 2016 5:06 pm
Location: Nicosia, CYPRUS

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.
User avatar
Harry Dalek
"Fester! Don't do that to 'Thing'"
 
Posts: 4491
Joined: Fri Sep 26, 2008 4:58 pm
Location: Australia

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.
Gregory
Research Scientist
 
Posts: 49
Joined: Wed Feb 10, 2016 5:06 pm
Location: Nicosia, CYPRUS

Previous

Return to Mechanical NBTV

Who is online

Users browsing this forum: No registered users and 20 guests