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 Gregory » Tue Feb 09, 2021 5:00 am

Andrew Davie wrote:In 3D printing, it is common to have the print surface (a plane) adjusted by 4 screws in the corners. This always bothered me; a plane is *defined* by three points, and it is about these that the plane pivots when they are adjusted. So, I get the same sort of vibe seeing 4-screws in a mirror adjustment. I understand why so, but still bugs the purist in me! Keep up the good work; am watching your construction with interest.

I agree with you Andrew, a 3 screw adjustment, although maybe not quite as rigid is better and I did notice when adjusting the mirrors on the original line frame 8 sided mirror, that if I was not careful the mirror surface could be easily warped, as acrylic does flex slightly. On the next try I will use a 3 screw adjustment instead and see what happens.
Gregory
Misunderstood Genius
 
Posts: 80
Joined: Wed Feb 10, 2016 5:06 pm
Location: Nicosia, CYPRUS

Re: Mini version of Scophony - its do-able

Postby smeezekitty » Tue Feb 09, 2021 8:16 am

Andrew Davie wrote:In 3D printing, it is common to have the print surface (a plane) adjusted by 4 screws in the corners. This always bothered me; a plane is *defined* by three points, and it is about these that the plane pivots when they are adjusted. So, I get the same sort of vibe seeing 4-screws in a mirror adjustment. I understand why so, but still bugs the purist in me! Keep up the good work; am watching your construction with interest.

One of my 3d printers has 3 screws to adjust build surface. I have to say it is _way_ easier to adjust it correctly with 4. 3 points define a plane but that doesn't mean it is the easiest to work with in practice.
smeezekitty
Just nod and pretend you understand me
 
Posts: 206
Joined: Fri Jan 29, 2010 11:42 am
Location: USA

Re: Mini version of Scophony - its do-able

Postby Gregory » Tue Feb 09, 2021 9:51 am

Andrew Davie wrote:Regarding micro-stepping in steppers this, too, has been something I've run across in 3D printing. The discussion there was the claim that layer height (the vertical stepping) should be a multiple of 0.04 mm. The argument ties down to avoiding micro-stepping the motor because it is inaccurate. The fundamentals are that the stepper driver is (depending on the brand) somewhat inaccurate at holding a motor at a micro-step position, and this translates to inaccuracies in layer height. While true enough, my analysis back in the day was that the actual error was too small to make any perceptible difference.

But in any case, interesting to see the same sort of thing being discussed in such disparate endeavours. Just be aware there is some positional error in microstepping, and this can vary between motors/brands. I could probably dig up the analysis/evaluation if really needed.

The Hackaday video is very informative. Hopefully the momentum of the mirror assembly and motor may assist in smoothing out inaccuracies of the micro-stepping. For the future, the 1.9 degree stepper motor would probably be a better option than the 7.5 degree motor I'm using for the line scan, as it would already have quite a high accuracy, even without the micro-stepping.
Gregory
Misunderstood Genius
 
Posts: 80
Joined: Wed Feb 10, 2016 5:06 pm
Location: Nicosia, CYPRUS

Re: Mini version of Scophony - its do-able

Postby Gregory » Tue Feb 16, 2021 5:12 am

The missing pulse restorer and frame separator are nearing completion and I should start testing soon.

However the line scanner with the 7.5 degree stepper motor together and 15 sided mirror troubles me somewhat as it will not only require a 2 stage multiplier, but will also require some way of phasing the mirror position with the incoming sync signal. This will need, at the least an opto sensor on the mirror together with the necessary electronics to achieve correct phasing.

One possible alternative solution would be to couple the motor to the mirror via a timing belt to provide a speed ratio of 15:48
As the mirror has 15 sides and the stepper motor has 48 full steps per revolution, with this ratio then 1 full step would equal 1 line scan, and thus the stepper motor could be driven directly from the line sync pulse.

Although this would theoretically mean lower output torque, because the stepper motor is operating at about a third of the original speed, the torque from the motor would be far higher and substantially compensate for this.

If this works the lines scan signal could drive directly the stepper motor and no phasing or Opto-sensor would be required, apart from setting up the initial angle position of the mirror to coincide with the start of the line scan. However the stepper motor would still need to be slowly accelerated to near the required speed, before syncing

So decisions, decisions, I have just ordered on eBay the timing pulleys, belts and idler pulleys required, and if it works (A BIG IF) this would simplify things substantially, for the line scan.

Any feedback or thoughts would be welcome, as I'm not sure if this will work.

The frame scan would still have to be done using the multiplier, as the speed would be too slow for smooth operation using full steps mode.
Gregory
Misunderstood Genius
 
Posts: 80
Joined: Wed Feb 10, 2016 5:06 pm
Location: Nicosia, CYPRUS

Re: Mini version of Scophony - its do-able

Postby Harry Dalek » Tue Feb 16, 2021 12:44 pm

Gregory wrote:
However the line scanner with the 7.5 degree stepper motor together and 15 sided mirror troubles me somewhat as it will not only require a 2 stage multiplier, but will also require some way of phasing the mirror position with the incoming sync signal. This will need, at the least an opto sensor on the mirror together with the necessary electronics to achieve correct phasing.


viewtopic.php?f=1&t=1795&hilit=mirror+camera

View this page this is how i did it and it worked very well using an opto switch !
Attachments
P1060669-crop.JPG
P1060669-crop.JPG (185.06 KiB) Viewed 2122 times
P1060678.JPG
P1060678.JPG (333.79 KiB) Viewed 2122 times
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: 4780
Joined: Fri Sep 26, 2008 4:58 pm
Location: Australia

Re: Mini version of Scophony - its do-able

Postby Gregory » Sun Feb 21, 2021 3:21 am

The missing pulse restorer is now fully working giving a continuous sync pulse, although there were some errors on the original schematic previously posted. I have now revised the schematic in the previous post as also shown below:

missing pulse restorer 3.jpg
missing pulse restorer 3.jpg (28.81 KiB) Viewed 2054 times

The restorer has been tested and setup for 30 lines (375 hz) and 60 lines (750hz). Other line/frequency resolutions can easily be added, with only one 22k preset required for each additional line/frequency resolution. The frame line resolutions has been kept at 12.5 hz which seems to be standard for most NBTV formats.

sync separator and missing pulse restorer.jpg
sync separator and missing pulse restorer.jpg (95.95 KiB) Viewed 2052 times

Oscilosope traces for the missing pulse restorer
The top trace is at the output of the first 4098 and the bottom trace is at the output of the restorer

30 LINES 375 HZ RESOLUTION

MPR1.JPG
MPR1.JPG (82.16 KiB) Viewed 2054 times

60 LINES 750 HZ RESOLUTION

MPR2.JPG
MPR2.JPG (74.69 KiB) Viewed 2054 times

The next stage is to connect and power up the line scan stepper drive and see how the line scan stepper motor reacts at 375hz and 750hz frequencies using a signal generator, and if all is well, try to run the stepper motors directly from the sync pulse signal.
Gregory
Misunderstood Genius
 
Posts: 80
Joined: Wed Feb 10, 2016 5:06 pm
Location: Nicosia, CYPRUS

Re: Mini version of Scophony - its do-able

Postby Harry Dalek » Sun Feb 21, 2021 8:24 am

Gregory what at the part values in the circuit ,a good circuit always comes in useful to us experimenting.
Good luck on the steppers !
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: 4780
Joined: Fri Sep 26, 2008 4:58 pm
Location: Australia

Re: Mini version of Scophony - its do-able

Postby Gregory » Sun Feb 21, 2021 10:06 pm

Harry Dalek wrote:Gregory what at the part values in the circuit ,a good circuit always comes in useful to us experimenting.
Good luck on the steppers !

Harry, Values for the restorer are as below. You can change the values of the RC combination, as long as the time constant remains the same. I used these values as I have loads of these, especially the 22k presets.

C3,C1 33n
C2 470n
D2,D1 1n4148
R1,R2 22k VAR
R4,R3 22k
R6,R5 47k
SW1 SW ROTARY 2P-6W
U1,U2 4098

The reason I did not include values, is that the frame line separator needs to be finished yet. I am hoping to get the frame pulse in a different way, by using an exclusive or gate. If this works, the frame separator can be used with any line scan frequency/frame rate combination, without any additional switching.
Last edited by Gregory on Wed Feb 24, 2021 8:29 am, edited 1 time in total.
Gregory
Misunderstood Genius
 
Posts: 80
Joined: Wed Feb 10, 2016 5:06 pm
Location: Nicosia, CYPRUS

Re: Mini version of Scophony - its do-able

Postby Harry Dalek » Mon Feb 22, 2021 3:56 pm

Gregory wrote:Harry, Values for the restorer are as below. You can change the values of the RC combination, as long as the time constant remains the same. I used these values as I have loads of these, especially the 22k presets.

C3,C1 33n
C2 470n
D2,D1 1n4148
R1,R2 22k VAR
R4,R3 22k
R6,R5 47k
SW1 SW ROTARY 2P-6W
U1,U2 4098

The reason I did not include values, is that the frame line separator needs to be finished yet. I am hoping to get the frame pulse in a different way, by using an exclusive or gate. If this works, the frame separator will work for any line scan frequency (using the missing pulse) and so the separator can be used with any line scan frequency/frame rate combination, without any additional switching.


No problems Gregory thanks for posting what's made so far ,i had a similar problem with my crt monitor using Steve's circuit it will now frame from 23 line to over 100 lines .. Keep going it will be nice to see it displaying in sync .
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: 4780
Joined: Fri Sep 26, 2008 4:58 pm
Location: Australia

Re: Mini version of Scophony - its do-able

Postby Gregory » Wed Feb 24, 2021 9:39 am

Just tested the frame line sync separator on 30 and 60 line resolution and all works fine. I have combined all the separate schematics into one, as below.
The pre- amp and line scan separator are copies of the Klass pre- amp and the NBTV sync separator. I have added to this the missing pulse restorer and frame line separator I built.

2020_sync restorer2_schematic .jpg

The complete separator has the following options/features

Connector outputs
1) Line scan sync output (with no missing pulse)
2) Line scan sync output (with the missing pulse)
3) Video output with restored DC level
4) Frame scan sync output with no phase delay. Operates with any lines scan frequency from 300hz to 800hz (6 switchable pre-set selections)

Front panel Controls
1) Amplifier gain
2) Frequency selection switch

Connector Inputs
1) 2 way connector for 12v DC
2) 3.5 mm Jack socket for Video input

As the breadboard construction is somewhat fragile next task is to design a proper PCB to replace this. This would also be a useful building block, that can be used on any televisor, and for future projects. When finished I will post all the details including the PCB artwork, components layout and parts list, for anyone that is interested.
Last edited by Gregory on Sun Apr 04, 2021 11:28 pm, edited 1 time in total.
Gregory
Misunderstood Genius
 
Posts: 80
Joined: Wed Feb 10, 2016 5:06 pm
Location: Nicosia, CYPRUS

Re: Mini version of Scophony - its do-able

Postby Harry Dalek » Thu Feb 25, 2021 4:46 pm

All looks great ,good idea to make this usable on a future project plug in i suppose ,thanks for the schematic i like trying different designs i will get around to trying it in the future.
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: 4780
Joined: Fri Sep 26, 2008 4:58 pm
Location: Australia

Re: Mini version of Scophony - its do-able

Postby Gregory » Sat Mar 06, 2021 8:49 am

I have temporarily connected the line scan mirror & motor to a stepper drive and a function generator to test the maximum line scan frequency possible

With 12v dc it was possible to ramp up the stepper motor to a maximum of 1600 full steps per second.
As the stepper motor has 48 full steps per revolution and the mirror has 15 faces the initial line scan frequency = 1600*15/48 hz = 500 hz.

With the intended belt gear multiplication of 3:1 and a 20v dc supply it should be possible to reach 800 hz (i.e. 64 lines at 12.5 frame rate)
As soon as the gears/belts are delivered we will find out.

In the meantime I have completed the design of the sync separator/pulse restorer PCB and etched and drilled the prototype as below:

separator_pcb.jpg
separator_pcb.jpg (117.95 KiB) Viewed 1852 times
Gregory
Misunderstood Genius
 
Posts: 80
Joined: Wed Feb 10, 2016 5:06 pm
Location: Nicosia, CYPRUS

Re: Mini version of Scophony - its do-able

Postby Andrew Davie » Wed Mar 10, 2021 4:38 am

smeezekitty wrote:
Andrew Davie wrote:In 3D printing, it is common to have the print surface (a plane) adjusted by 4 screws in the corners. This always bothered me; a plane is *defined* by three points, and it is about these that the plane pivots when they are adjusted. So, I get the same sort of vibe seeing 4-screws in a mirror adjustment. I understand why so, but still bugs the purist in me! Keep up the good work; am watching your construction with interest.

One of my 3d printers has 3 screws to adjust build surface. I have to say it is _way_ easier to adjust it correctly with 4. 3 points define a plane but that doesn't mean it is the easiest to work with in practice.


Late response, but I suspect your error there is leveling in the corners of the bed.
You should level above the pivot points -- the three screws, in other words, The height at these points does not change when you adjust the others.
User avatar
Andrew Davie
"Gomez!", "Oh Morticia."
 
Posts: 1584
Joined: Wed Jan 24, 2007 4:42 pm
Location: Queensland, Australia

Re: Mini version of Scophony - its do-able

Postby Harry Dalek » Thu Mar 11, 2021 2:38 pm

Beautiful PCB all very professional...much better than i could ever do .
Hope the tests are going well .
Trying a smaller laser you will have to put up with a tiny raster might also be a bit dim but fine for testing till you get something better .
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: 4780
Joined: Fri Sep 26, 2008 4:58 pm
Location: Australia

Re: Mini version of Scophony - its do-able

Postby Gregory » Sun Mar 14, 2021 9:44 am

Sync/restorer PCB should be finished this week, if all goes well.

The timing belts and pulleys have finally arrived so should be able to do the first tests for the line scan motor/mirror. Initially I am hoping to make a temporary base to mount the motor, belts, pulleys and mirror together. Then the scan motor together with the mirror can be tested to see the maximum RPM possible, anything above 3000 RPM at the output would be OK. Initially I will use a 555 timer, as a pulse oscillator with a slow ramp up to the max frequency. If this works, then I can make the final base for the line scan assembly.

belt.jpg
belt.jpg (29.63 KiB) Viewed 1691 times
Gregory
Misunderstood Genius
 
Posts: 80
Joined: Wed Feb 10, 2016 5:06 pm
Location: Nicosia, CYPRUS

PreviousNext

Return to Mechanical NBTV

Who is online

Users browsing this forum: No registered users and 9 guests

cron