Mini version of Scophony - its do-able

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Re: Mini version of Scophony - its do-able

Postby Harry Dalek » Fri May 13, 2016 3:13 pm

HI there what i did is i used a u shaped opto switch placed so the edges of the line mirror brake the light is a lot easier and gives an excellent pulse ,the mirrors so so well designed there is no mistake between pulses when the light is broken .

On the mirror camera try my own circuit using a 555 bistable switch as the PLL replacement that worked so well Gary was surprised it was mechanical sync.

I have never tried the HD as a powered motor on one of these things but i have many times used it to rotate a mirror drum or disc ,i used a pulley system using a dc motor to do the grunt work !

I have to review your posts as to how you a using the PLL ...you need a good clock 4066 crystal controlled ? A circuit is on the forum ,so you want a no drifting 400hz clock what i do is use a opto switch feed that sinewave pulse into a comparator LM311 i use and then the square wave mechanical sync pulses into one side of 555 bistable inputs and the crystal or good RC 400hz osc pulse to the other ,the bistable switch switches the transistor that controls the motor ...i use a LM317 on the positive of the motor as they are all different and need different voltage so the transistor pulses can control the motor to much or to little voltage here your motor will not control its speed....if you use a RC clock you can adjust it and see the motor slow down or speed up ....Its an not easy thing to control a motor its an art !
Don't give up its hard but possible ....to start you need to used your mirrors corners as the mechanical timing ...no matter how close you think you have made a hand made thing to get the pulses off there will be mistakes your pulses will be different so oscillating .
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 May 13, 2016 7:36 pm

Hi Harry,

Thanks for the info and yes I will try using the edge of the mirror to get the pulses, the simpler the better, and I can do the same for the frame sensor.
If you can please can you send me the bi-stable circuit you used instead of the PLL, sounds very interesting.

With the hard disk motor unfortunately, it is very difficult to control the speed up and down quickly as it has an extremely low torque although it has unbelievable top speeds. With DC motors and stepper motors you have lots of torque which makes it easy to control. As the 7.5 degree stepper motors are very cheap, that is the way I will go as they provide precise speed providing your clock frequency is stable.

The only thing with the steppers, they must have low resistance/inductance windings in order to have the high stepping rates needed. The one I have measures 5.8 Ohms and that works fine past 5000 RPM with 24v for the driver, but I noticed on the web there are some with only 2.5 ohms, they should fly.
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Re: Mini version of Scophony - its do-able

Postby Harry Dalek » Fri May 13, 2016 8:59 pm

Gregory wrote:Hi Harry,

Thanks for the info and yes I will try using the edge of the mirror to get the pulses, the simpler the better, and I can do the same for the frame sensor.
If you can please can you send me the bi-stable circuit you used instead of the PLL, sounds very interesting.


Hi Gregory
It was not my originally idea Steve and Gary mentioned once it would pretty much do the same thing as a PLL bit easier to understand no one has really worked out the operation of the 4046 works but so does a 555 timer bistable for motor control i use a bistable i tried it and it worked .

With the hard disk motor unfortunately, it is very difficult to control the speed up and down quickly as it has an extremely low torque although it has unbelievable top speeds. With DC motors and stepper motors you have lots of torque which makes it easy to control. As the 7.5 degree stepper motors are very cheap, that is the way I will go as they provide precise speed providing your clock frequency is stable.


I have used stepper motors for the line motor via again a pulley system slow to get up to speed and do clog stop if you push them to fast and you have to start them from the slow speed again ...i think for nbtv speeds a dc motor is quicker and easier......fine and better for SSTV line speeds but ...
I understand your problem with the HD motor if you can get a thin vcr tape machine rubber band to fit and move your HD shaft it would be a very easy fix to connect that and to a dc motor to drive it ....it is best to direct drive i would say but its hard to connect some thing with out alignment and stopping wobble and such so using a HD as the thing to rotate something such as your mirror is a good idea ! its easier to make that rotate via another motor ...more messy but in ways less of a headache .

The only thing with the steppers, they must have low resistance/inductance windings in order to have the high stepping rates needed. The one I have measures 5.8 Ohms and that works fine past 5000 RPM with 24v for the driver, but I noticed on the web there are some with only 2.5 ohms, they should fly.
[/quote]

Great idea for the frame mirror but from what i have tried i would rather use a old DC any day for NBTV line speeds unless you use a big pulley wheel then you can run the stepper slow and and make your mirror HD shaft rotate fast .

Heres one of my motor control circuits forget about A and B parts of the circuit but i suppose the B would control your frame motor as i was trying this to vibrate a relay with a mirror it would run a motor instead ....reason i used a RC oscillator instead of the crystal oscillator ....the crystal would give you better line control ...but i had the problem i wanted that 4060 to give me both as i recall thats the reason i went with a RC version .....i would put in a lm317 for the polygon or your dc motor if you try it you can adjust the motor more to get itin range to be controlled via the transistor switching ...it was pot luck 12 volts was fine for mine /
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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 » Sat May 14, 2016 3:16 pm

Harry, will definitely try the bistable for sync, I like the idea, its simpler in operation. Should be able to do a test on the line scan and sync with the new motor first part of next week, as I need to make a new flange for the stepper motor first. If this doesn't work than I will go for a DC motor, but I think it will.
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Re: Mini version of Scophony - its do-able

Postby Harry Dalek » Sat May 14, 2016 5:49 pm

Gregory wrote:Harry, will definitely try the bistable for sync, I like the idea, its simpler in operation. Should be able to do a test on the line scan and sync with the new motor first part of next week, as I need to make a new flange for the stepper motor first. If this doesn't work than I will go for a DC motor, but I think it will.



HI Gregory
I am not sure how many people have ever tried it but i have been happy with it ,things that do effect the result is if using a pulley system the rubber band tension should not be to tight so reason i had the little motor movable for adjusting this .
viewtopic.php?f=1&t=1435&hilit=bistable

If i could of i would rather direct drive but some times you have to make do with the junk you are using and make it work or try .

I have tried steppers as i said should be fine for 32 line any more you will need pulley wheel i got up to 60 line with the slit drum monitor ,
might be worth a look same sort of idea .

viewtopic.php?f=1&t=1486&hilit=new+drum+monitor

viewtopic.php?f=1&t=1517&hilit=drum+monitor

I did start off with the idea with this one to use steppers for both drums i ended up replacing the line one with a dc motor

Unfortunately the line drum dvd disc case was i found out a little prone to vibration wobble more so at the higher speeds i wanted a disaster if you have a look at the last pictures .

Changing things is the way it gos with these things Gregory some times things work out others (most of the time not) for me but its fun trying ,yes see how you go with the stepper motor .
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 » Wed May 18, 2016 7:12 pm

After a lot of playing about , success at last with the line scan motor. The original hard disk motor was replaced with a Matsumi 7.5 degrees stepper motor, after making a flange to accept the 3 mm spindle of the motor, and the polygon mirror.

Initial tests with the stepper driver, it was possible to squeeze a maximum of 3000 RPM at 24 V dc with the mirror mounted, which was not acceptable, as torque was low and slightly more speed was needed. I then looked at the small PCB on the motor used for connecting and noticed the 4 windings were connected as 2 pairs in series. In order to reduce the resistance and the inductance of the 2 pairs of windings, I modified this to put them in parallel, thus reducing the resistance from 5.6 ohms to 1.4 ohms per winding pair.

The motor now could spin at 3200 RPM with 12 V dc on the stepper drive and at 24 v it spun over 5000 rpm, although at this speed the bearings were more noisy. The noise may be due to the fact this was an old motor stripped from a copier and I noticed the bottom bearing had small play, but at 3200 RPM it ran much smoother.

The final supply will be set to 15-18 V dc for the stepper drives and 12 V dc for the rest of control circuitry, with the 15 V providing ample torque at 3200 rpm which is the maximum speed I will use at the moment.

So for the 3 NBTV standards with the 15 sided mirror we have

32 lines at 12.5 frames per second = 1600 RPM
48 lines at 12.5 frames per second = 2400 RPM
64 lines at 12.5 frames per second = 3200 RPM

The motor was run on 1/16 micro-steps so the pulse rate for 3200 RPM is 48 x 16 x 3200/60 = 40,960 pulses per second.

The other encouraging thing, was that now the stepper motor stops in less than 2 seconds if the clock is stopped, whereas with the hard disk drive motor it would take over a minute to stop, so the motor should be far better to control. Providing I don't hit on any other unforseen problems I should have a stable televisor with sync within a week or so.
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Re: Mini version of Scophony - its do-able

Postby Gregory » Sun May 22, 2016 9:49 pm

Finally the line scan sync is working well. I experimented using a 4046 PLL ic and as an alternative using a bistable for the line sync.
Both worked, but for this televisor it seems the bistable performed better, although phasing has to be done manually.

As it is intended this televisor should be suitable for the following standards

1( NBTV standard 32, 48, and 64 lines at 12.5 frame/sec
2) Baird 32 lines at 12.5 frames/sec
3) 32, 48 lines at 20 frames/sec
4) Other standards to a maximum of 1000 line scans/sec (if possible)

The following controls will be needed to achieve this:

1) Line scan frequency from 300 - 1000 line scans/sec
2) Frame scan frequency from 10 - 30 frames/sec
3) Sync/phase switch
4) Sequence switch (i.e scan LRTB, LRBT, RLTB, RLBT)

Basically after selecting the right sequence the line and frame frequency controls are adjusted to obtain the steadiest picture possible and then the sync/phase switch is turned on to lock the picture.

The only bit on the line scan, at the moment needs re-doing is the sync separator. I intend using the club version of this, which should be far better but unfortunately I cannot get the CA3140 or CA3240 IC locally, so again a little delay here.

Once this is complete I intend designing the first PCB for the line scan with frequency control
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Re: Mini version of Scophony - its do-able

Postby Harry Dalek » Mon May 23, 2016 12:11 am

HI Gregory i made the club circuit with another IC which was not to bad for a sync sep circuit posted below ,i ended up using for the sync sep a AN1358.

Also with higher line speeds with a stepper you really are better off using a pulley system you get a lot more speed at the mirror with less grunt work from the stepper motor...i forgot what i did for the 1meg resistor at the sync sep try a resistor wheel till you get the correct filtered pulse ,i just know it worked with that ic if you have it handy .

viewtopic.php?f=10&t=1982&hilit=sync+sep
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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 Steve Anderson » Fri Jun 17, 2016 1:14 pm

Hi Gregory, I received your e-mail via this forum. The problem with e-mails via the forum is if I 'reply' as you usually would my reply goes to the administrator which he/she has to forward on - not ideal. It's better to use a PM which works as you would expect...you can also add attachments to PMs.

Anyway, I need a little information on the lasers (both powers), the nominal voltage and current when used at 100% brilliance.

Steve A.
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Re: Mini version of Scophony - its do-able

Postby Gregory » Sat Jun 25, 2016 8:25 pm

At last have now finalised the circuits for both the line and frame syncs and motor controls - should be able to upload schematics of these in the next few days. It now remains to design the PCB for this section, to complete.

The only remaining circuit left after this is the laser modulator. I am at the moment using a linear driver for this, which is not bad, but not great. I have also now made progress with a PWM modulator, although performance at the moment is only marginally better than the linear driver

Unfortunately I blew up the last laser diode and am waiting for new ones to arrive, Does anyone know what PWM frequency to use for 60 lines 12.5 frames/sec? I have tried frequencies up to 500khz. Hopefully as soon as the new laser diodes come I will be able to finalise this too.
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Re: Mini version of Scophony - its do-able

Postby Harry Dalek » Sun Jun 26, 2016 4:56 pm

Gregory wrote:At last have now finalised the circuits for both the line and frame syncs and motor controls - should be able to upload schematics of these in the next few days. It now remains to design the PCB for this section, to complete.

The only remaining circuit left after this is the laser modulator. I am at the moment using a linear driver for this, which is not bad, but not great. I have also now made progress with a PWM modulator, although performance at the moment is only marginally better than the linear driver

Unfortunately I blew up the last laser diode and am waiting for new ones to arrive, Does anyone know what PWM frequency to use for 60 lines 12.5 frames/sec? I have tried frequencies up to 500khz. Hopefully as soon as the new laser diodes come I will be able to finalise this too.



I know what its like loosing a laser they are very touchy , best to keep it at its operating voltage no higher and a touch lower would not hurt ,i have always used a LM317 to do the adjusting but as i was told the trimmer is not a good idea if it fails .

Not sure about the correct band width but 500khz seems to high for 60line 32 PWM oscillator is around 40 50 khz so would it be double for 60 or a bit lower round the 100khz range ?

Looking forward to seeing your monitor running ...do you have contrast and brightness control my laser SSTV had some good control over the UV laser but don't think it was great for my NBTV try.... different circuits and all .
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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