Magnetic replacement for the opto fork ?

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Magnetic replacement for the opto fork ?

Postby Harry Dalek » Sat Dec 17, 2011 4:58 pm

Its a bit easier for a drum type monitor but i was thinking about an old episode of The Secret Life Of Machines...where they explain magnetic recording they make a band saw into a primitive audio recorder just using some made up electromagnets .

http://www.youtube.com/watch?v=apt8TgJLXXo

Well the idea on the drum would be to tape or glue audio tape around the drum where the 32 line spacing should be wipe a small magnet over that space or record a pulse via a electromagic i think you can work out the rest ..if you watch that part of the episode it could be used for a opto fork replacement...

Could do it on a nipkow via doing the same cutting a pasting magnetic tape strips or iron filings.

If its easier of harder than a normal opto fork or better or worse just an idea popped in my head .
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Postby DrZarkov » Sat Dec 17, 2011 6:04 pm

It should work, indeed, and you are not the first one with that idea: http://www.earlytelevision.org/fracarro_30_line.html
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Postby Harry Dalek » Sat Dec 17, 2011 6:59 pm

DrZarkov wrote:It should work, indeed, and you are not the first one with that idea: http://www.earlytelevision.org/fracarro_30_line.html


Oh yes i see how hes works has bolts where the holes would be of an opto fork looks like an electro magnet one side and a pick up coil other side so as the bolt passes transmits a pulse to the pick up coil ...well i think it works like that ..

Yes baird had same sort of idea with a tooth wheel doing the same sort of thing i suppose .

My idea i just don't know if its better or not ...much a muchness as they say .
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Postby Steve Anderson » Sat Dec 17, 2011 10:09 pm

On a bicycle-logger I built (how environmentally responsible?) I used a small permanent magnet attached to one wheel and a Hall-effect device to count revolutions and thereby work out distance traveled.

It's a solid-state replacement for a reed-switch but available in logic output versions to replace reed-switches as well as linear versions.

They're not sensitive to ambient light or vibration, ideal on an old bone-shaker...I'm talking about the bike.

Worth investigation, they're fast enough for NBTV disc/drum position sensing whereas a reed-switch probably isn't...and of course don't wear out. Hall-effect devices are very common in DC brushless motors to provide commutation information to the controller. They're used in cheap DC fans for PCs as well as VCR head-drum position sensing so they're plenty fast enough.

Steve A.

P.S. A variation on the above., still magnetic and still with the small magnet on the disc/drum. Use an record/playback head from a old cassette recorder, this should produce a pulse as the magnet swings by. No idea on the signal amplitude though...except probably quite low.
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Postby Harry Dalek » Sun Dec 18, 2011 11:52 am

Steve Anderson wrote:On a bicycle-logger I built (how environmentally responsible?) I used a small permanent magnet attached to one wheel and a Hall-effect device to count revolutions and thereby work out distance traveled.

It's a solid-state replacement for a reed-switch but available in logic output versions to replace reed-switches as well as linear versions.

They're not sensitive to ambient light or vibration, ideal on an old bone-shaker...I'm talking about the bike.

Worth investigation, they're fast enough for NBTV disc/drum position sensing whereas a reed-switch probably isn't...and of course don't wear out. Hall-effect devices are very common in DC brushless motors to provide commutation information to the controller. They're used in cheap DC fans for PCs as well as VCR head-drum position sensing so they're plenty fast enough.

Steve A.

P.S. A variation on the above., still magnetic and still with the small magnet on the disc/drum. Use an record/playback head from a old cassette recorder, this should produce a pulse as the magnet swings by. No idea on the signal amplitude though...except probably quite low.



The hall effect device sounds good have to look if i can find one in the places you say have lots of old vcrs to scrap .

I just found out my motor might just have them attached ,its out of a 80s video disc player the record sized type, hooking my scope up to the extra 2 wires i get a sign wave frequency go's up and down with the motor speed ..

The magnetic tape idea reusing the head off a tape player would be good
could go all out bit of a over kill using a loop in a cassette and keep the player..either get your disc drum motor to work replace the player motor or loop the tape out to the monitor motor some how ...but all that sounds like to much work for me ..simple ideas are always better.
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Postby Steve Anderson » Sun Dec 18, 2011 6:35 pm

Harry, here's a very typical place you'll find them on a VCR head-drum assembly. They're the three square chips located at the bottom right of the PCB in the attached picture. Note they're spaced at 30° intervals.

But you may come across some head-drum assemblies that have none, in that instance the controller uses the back-EMF of the motor for sensing.

Steve A.
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Hall Detector 1.jpg
Hall Detector 1.jpg (64.89 KiB) Viewed 4339 times
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Postby Harry Dalek » Sun Dec 18, 2011 8:22 pm

Steve Anderson wrote:Harry, here's a very typical place you'll find them on a VCR head-drum assembly. They're the three square chips located at the bottom right of the PCB in the attached picture. Note they're spaced at 30° intervals.

But you may come across some head-drum assemblies that have none, in that instance the controller uses the back-EMF of the motor for sensing.

Steve A.


Hi steve you have got me interested in these things !

I just got 5 coming via ebay free postage for 2 dollars or so.

Yes i noticed they use 3 from checking out sites about them...

i should think we only need one as in a opto fork...need a few tiny magnets replacing the holes in a opto fork but mmm

i will pull some stuff apart see if i can find some too as you say its worth a try .
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Postby Steve Anderson » Sun Dec 18, 2011 8:56 pm

harry dalek wrote:...i will pull some stuff apart see if i can find some too as you say its worth a try .


I used one of those three in the photo for the bike-logger. They're a bit fiddly but you can get standard tranny-like packaging as well. These were linear and needed a comparator to follow them to produce logic-level signals. The downside of Hall effect devices is they use around 10mA of current. Not an issue in a NBTV monitor which is usually mains-powered, but took some working around on a battery-powered bike-logger.

A note. If you place a small magnet near the periphery of a disc/drum you'll probably have to balance it out with a similar non-Ferrous mass diametrically opposite, Brass, Aluminium, heavy plastics, even glass.

Steve A.
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Postby Klaas Robers » Sun Dec 18, 2011 10:21 pm

harry dalek wrote:I just found out my motor might just have them attached ,its out of a 80s video disc player the record sized type, hooking my scope up to the extra 2 wires i get a sign wave frequency go's up and down with the motor speed .


I think that is the same Laservision-player motor I use in my monitor. It is a nice motor and the magnetic pick-up gives indeed a nice sinewave from the permanent magnetic ring, a sinewave that can be limited to a square wave. The bad news is: it gives 18 sinewaves per revolution. It took me more than a year to find out how to match the 18 sine waves to the 32 sync pulses. I even thought of remagnetizing the permanent magnetic ring to 32 sinewaves, or if that doesn't work, 16 sine waves.......

At the end I found a way to synchronise the 18 waves to the 32 syncpulses, however it was rather complex and I fear too difficult to describe here.
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Postby DrZarkov » Mon Dec 19, 2011 4:50 am

Maybe it would be easier to make a new disc with 36 apertures...
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Postby Harry Dalek » Mon Dec 19, 2011 7:12 pm

Klaas Robers wrote:
harry dalek wrote:I just found out my motor might just have them attached ,its out of a 80s video disc player the record sized type, hooking my scope up to the extra 2 wires i get a sign wave frequency go's up and down with the motor speed .


I think that is the same Laservision-player motor I use in my monitor. It is a nice motor and the magnetic pick-up gives indeed a nice sinewave from the permanent magnetic ring, a sinewave that can be limited to a square wave. The bad news is: it gives 18 sinewaves per revolution. It took me more than a year to find out how to match the 18 sine waves to the 32 sync pulses. I even thought of remagnetizing the permanent magnetic ring to 32 sinewaves, or if that doesn't work, 16 sine waves.......

At the end I found a way to synchronise the 18 waves to the 32 syncpulses, however it was rather complex and I fear too difficult to describe here.


Hi Klaas

Yes thats what i am using i was expecting the 2 extra wires were for some sort of motor control but never really looked into it till the other day ...Yes gives a nice sine wave where the frequency increases with motor speed...
I was wondering if any one had tried it for nbtv syncing ,i recall on a passed post you had this type of motor but i didn't know you got it working .

Sounds i have no hope if you are had trouble !

BTW do you know the max rpm the motor can do also the top voltage it can be run at ...i'm running at 20 or so ...i'd say this thing can do more than what i am pushing it .

I was thinking of tacking on a small disc to the back as theres another connection to the motor shaft there as well...so i could use that to make a little opto fork disk or magnetic what not ..i was trying my drum slits but they must be to narrow to use for the fork idea ....so looks like i have to rethink this one.
:roll:
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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Postby Klaas Robers » Wed Dec 21, 2011 7:03 am

Harry, this motor is designed to run at 25 rev/sec. with the load of a rather heavy VLP-disc of 30 cm diameter. However I think it may run even faster, 50 rev/sec.

The motor runs 12,5 rev/sec on a voltage of about 5 volts.

The trick I used is that I made the genlockable EPROM picture generator and genlocked that onto the incoming video (sync pulses). Then I programmed a pulse signal in the EPROM having 18 pulses per NBTV frame. Those pulses I used to synchronise the motor on with the 18 pulses per revolution. I used the 4046 for that.

The nice thing is that you can program almost every pulse pattern in the EPROM. So the number of pulses per revolution is relatively unimportant.
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Postby Harry Dalek » Thu Dec 22, 2011 11:39 am

Klaas Robers wrote:Harry, this motor is designed to run at 25 rev/sec. with the load of a rather heavy VLP-disc of 30 cm diameter. However I think it may run even faster, 50 rev/sec.

The motor runs 12,5 rev/sec on a voltage of about 5 volts.

The trick I used is that I made the genlockable EPROM picture generator and genlocked that onto the incoming video (sync pulses). Then I programmed a pulse signal in the EPROM having 18 pulses per NBTV frame. Those pulses I used to synchronise the motor on with the 18 pulses per revolution. I used the 4046 for that.

The nice thing is that you can program almost every pulse pattern in the EPROM. So the number of pulses per revolution is relatively unimportant.


Klaas thats pretty good near on 3000rpm if it can do it ...i know its doing better than 1500 ,i did a google and they say they run at 1500 normally and 1800 depending on pal ntsc ..

I have a few of those never knew why those chips i had had a window till i read about the programing and wiping the memory ...never really played with those ever so something i need to read and learn about ,i was thinking you were using a Shift register or something like that .

What did your motor end up in Klaas ? i have seen you have a mirror screw
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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Postby Klaas Robers » Fri Dec 23, 2011 2:46 am

Harry,

my motor is running an aluminium Nipkow disc monitor. If you look at the Convention photo reports in the Gallery of NBTV.org you may see it. It's a square wooden box monitor, normally closed, but at the Convention also shown open.
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Postby Harry Dalek » Fri Dec 23, 2011 4:20 pm

Klaas Robers wrote:Harry,

my motor is running an aluminium Nipkow disc monitor. If you look at the Convention photo reports in the Gallery of NBTV.org you may see it. It's a square wooden box monitor, normally closed, but at the Convention also shown open.



Hi Klaas

I will have a look ...i think the box part is the hardest thing on a monitor to make ..i don't know if electronics and wood work go together or its hard to have both skills :oops:

Steves idea of using the Hall effect sensor got me interested to try ..i have placed some tiny magnets around my drum testing it and these things give a nice signal .

I was going to use a strip of fridge magnet type rubber and cut out thin strips , the signal pulse it gives is lowwer than the little magnets i am using and only reason i have gone with the tiny magnets is i had them and looks neater ...
I have ran the motor with them and does not seem to cause any problems and the pulses from the hall effect sensor look good .
Attachments
Picture 194.jpg
i am going to try a hall effect sensor for a fork idea ...see little magnets
Picture 194.jpg (118.74 KiB) Viewed 4248 times
ugn3503.pdf
this is the sensor i am trying notice different ways you can use it ...i like the detecting of gears cogs when they are close
(151.34 KiB) Downloaded 139 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.
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