MUTR-kit circuit diagram

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Postby AncientBrit » Thu Feb 12, 2009 3:04 am

Thanks Steve, Klaas, very useful practical information.

Regards,


Graham
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Postby Ralph » Thu Feb 12, 2009 3:37 am

Graham,

As Klaas noted, the sole purpose of the diode is to protect the FET from the usual inductive "spikes". Without an external resistive load the braking effect is nil. I was quite amazed, given the low inertial load of the disc, how long it takes the system to spin down after power is removed!

With respect to the motor drive, there are almost certainly other engineering solutions, but my focus has been on the utter simplicity of the MUTR variations on other people's circuits. A recurring theme on this forum has been the need for a simple electronics package, suitable for novices, that will run a mechanical televisor with a satisfactory level of performance. Thus was born the idea of a simple, single circuit board solution. The engineering changes I am making are trivial:

(1) All operating voltages are regulated and all bias levels are referenced to a regulated 5V bus.

(2) The LM324N will be operated off a regulated 12V supply instead of the 6V used in the MUTR version. The 324 is a rugged little package, but the op-amps are a bit sluggish at that voltage in single-ended service. There is no potential for limited bandwidth at 12V!

I am also experimenting with a variable phase-delay that would let one "zero-out" any phase errors due to the placement of the chopper graphic or the optical sensors. There is room on the board for this function, I just don't know if is worth the effort.

Ralph
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Postby AncientBrit » Thu Feb 12, 2009 5:05 am

Ralph,

I understand your concerns about keeping it simple.

The pix phasing control would be a useful addition but it might be "overkill" given the elegant simplicity of the current setup.

(And Klaas has offered a solution, glue on a replacement strobe in a slightly rotated position)

Thanks for your feedback. Keep us informed of your progress.


Kind regards,


Graham
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Postby DrZarkov » Sun Feb 15, 2009 7:30 pm

Does anybody know what kind of opto-coupler is used in the MUTR-kit? I looked at www.conrad.de, but only found the "classic" way with the combination of separate phototransistor/IR LED or that sloted opto-switch you find at the club sales (BTW very much more expensive at Conrad). Are there suitable ways of replacing it?
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Postby Klaas Robers » Sun Feb 15, 2009 8:48 pm

I never had seen it before. It looks like a separate LED and phototransistor with a black sleeve over it. However in the UK very remarkable components are available.

But I am not enthousiastic about it as the sensitivity is strongly dependant on the distance of the disc. When it is not really flat and wobbles the sensitivity is constantly changing. This is a disadvantage for the synchronisation.
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Discs supplied in error recently

Postby acl » Mon Feb 16, 2009 1:37 am

Please note: Due to an error with a small batch of CDroms; some customers may find their CD to be in the wrong format. Please contact us for a free replacement.
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Postby Ralph » Mon Feb 16, 2009 2:59 am

The one I am using is a Fairchild QRD1114, which is widely available and quite inexpensive. You can download the data sheet:

http://www.engr.ucsb.edu/~mdnip/me170c/ ... RD1114.pdf

Works well at sensing distances between 3 and 6mm so will accomodate a "wobbly" disc.

There are some very nice integrated reflective sensors available, complete with internal schmidt triggers to provide clean TTL output and long-distance sensing capability.. The problem with these units tends to be their frequency response. Many will only reach 100 Hz! To generate a clean trigger from our 400 Hz sync, one needs a much faster response. Hence the use of basic phototransistor outputs with external circuits to boost and sharpen the response.

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Postby Klaas Robers » Mon Feb 16, 2009 5:34 am

Chris,

I got a wrong format CD and I would like to have a better disc, a normal audio-type of CD. However I managed to get the video off the CD-ROM files and rearranged them such that they form now an uninterrupted NBTVideo stream, seamless over the borders of the tracks. I read that this was not the case in the original CD-disc. Are you interrested in it, then I can send you a disc with all the files on there to produce uninterrupted CD's.
I did not know that You are part of the MUTR-bussiness.

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Postby AncientBrit » Mon Feb 16, 2009 6:34 pm

I took delivery of the MUTR kit last week and spent an hour assembling it. I have to say I am very impressed with the quality of the whole kit.
It worked first time, the accuracy of the hole punching in the disc is spot on, no overlaps visible on the pix.

A few alterations, and additions I carried out:

I used white Tippex to fill the engraved line on the front panel.

I moved the lens as far forward as possible on the spacers separating the two panels.

I moved the LED further backward by adding 15mm spacers to reduce the hot-spot and to give a wider coverage.

I've flattened the disc as much as possible and positioned it so that it's about 3mm from the opto pickup.

I also removed the gearwheel and placed it on the other face of the disc so you push the disc onto the face rather than separating it.

I mounted the battery box so that the removable lid faced outward making battery changing slightly easier, you need to make sure the switch clears the panel and the bottom of the battery box does not come below the lower edge of the legs.

I note that the diffuser provided seems to produce speculars, I might try an alternative.

Line lock is available over much of the pot travel but the centre position is out by 1/2 line.
Frame lock is not consistent, sometimes it's out by a line depending on run up.

On the whole a very good kit and introduction to NBTV.

Regards,

Graham
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Postby Klaas Robers » Tue Feb 17, 2009 11:51 pm

Graham, how have you flattened the disc?

I have the same misallignment over half a line. So I got the pdf of the stroboscopic disc. I can print that and glue it on top of the existing sync-disc.

For an experiment connect your oscilloscope at the terminals of the motor. When correctly synchronised you will see a 12,5 Hz sine wave. When wrongly synchronise you see a pulse in the sine wave.

I should do experiments with a resistor in series with the motor, as Pete Smith recommends. Now I have a resistor of 12 ohms in parallel with the motor and that improoves the synchronisation already. But still I have 3 sync possibilities: correct, one line too early, one line too late.
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Postby Klaas Robers » Wed Feb 18, 2009 4:02 am

Graham, how have you flattened the disc?

I have the same misallignment over half a line. So MUTR sent me the pdf of the stroboscopic disc. I can print that and glue it on top of the existing sync-disc, of course with some rotational offset.

For an experiment connect your oscilloscope at the terminals of the motor. When correctly synchronised you will see a 12,5 Hz sine wave. When wrongly synchronised you see a pulse in the sine wave.

I should still do experiments with a resistor in series with the motor, as Pete Smith recommends. Now I have a resistor of 12 ohms in parallel with the motor and that improoves the synchronisation already. But still I have 3 sync possibilities: correct, one line too early, one line too late.
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Postby Jim Wood » Wed Feb 18, 2009 12:28 pm

Well, I'm "totally stoked," as the local surfers say; I got my MUTR kit in the post today... all intact and by far the best value of anything I've purchased in a long time. Can't wait to get it going, and thanks all for the tips!
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Postby AncientBrit » Wed Feb 18, 2009 6:38 pm

Klaas, I straightened the disc as best I could by bending it in the opposite direction!

As you say the motor servo is good but can lock in one of three
positions, +1 line, correct, -1 line.

I'm thinking about an add on circuit that detects the frame out of phase and gives a "kick" to move it to the correct phase.

But I'm still very impressed with the design and implementation.

And at least MUTR acknowledge the design is by club members,


Regards,


Graham
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Postby gary » Wed Feb 18, 2009 7:25 pm

My understanding that it was the nature of this circuit to be one line out (Newsletters Vol 32 2 and 3).

After about a year my disk became so badly warped that I decided to try to heat the disk up using a hot air gun (don't try this at home unless your disk is already pretty unusable) and then sandwiching the disk between heavy layers of melamine. This worked OK at first but within hours the disk resumed it's warped shape as if it has shape memory.

It would be nice if a batch of very thin stainless steel disks of the right size for the MUTR could be ordered by the association and offered for sale.
gary
 

Postby AncientBrit » Wed Feb 18, 2009 11:33 pm

re flattening the disc.

You could try glueing/double-sided taping a thicker piece of card to the existing disc.
Of course the diameter has to be less than the inner most hole.
Might improve things a bit. I'll try that out later.

Regards

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