Cutting out sync pulses.

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Postby Klaas Robers » Wed Oct 19, 2011 6:14 am

In practice the 4046 PLL for a Nipkow disc with a missing sync pulse will synchronise one line shifted. I see this in the MUTR televisor and I have seen it in the Peter Smith and Grant Dixon monitors as well. If the phase difference is more than one line the correction pulse is so long that the disc will slip one line in a revolution. But with one line offset the corection pulse is to short.

With correction by hand (gentle braking) it is possible to synchronise properly. The correction wave form is perfect in this case and the disc keeps its synchronisation. But when you let it go from not synchronised situation it will most of the time come to one line offset. This can be seen best on the Grant Dixon test pattern, where left and right should show equal 2 lines width grey scales. If one line is swapped from left to right or reverse you will see that clearly.
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Postby Steve Anderson » Wed Oct 19, 2011 9:00 pm

Some of you may be aware that we've had severe flooding here in Bangkok and many other parts of Thailand, but thankfully we're on higher ground and (thus far) it's had no effect upon us. With that in mind I went to my usual 'electronics souk' today to get some HEF/CD4046 chips having tossed out all my previous stock of HEF/CD chips years ago.

Of the six suppliers I generally use, not one stocks them any more...."No demand" was the usual response...not just the 4046, but the entire 4000-series range...

I do have some antique HC series versions (post HEF-era), I see that Farnell in the UK still stocks the HEF4046 but that will take a bit of time to get here...

I guess it's a product of being 40-year old technology...

Steve A.
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Postby gary » Wed Oct 19, 2011 9:14 pm

Odd isn't it? as this mob:

http://www.futurlec.com.au

who ship from Thailand, stock them. They are a bit slow on delivery when ordering from Oz, but maybe you would get quicker delivery.
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Postby Steve Anderson » Wed Oct 19, 2011 9:49 pm

gary wrote:http://www.futurlec.com.au ...who ship from Thailand...


Not particularly, probably around the same delivery time, a few days. But having said that I've only ordered from them a few times...but one thing I will say, forget any support...no response in any manner to a number of e-mails sent to them...so, make sure you know what you're ordering...if you have a question about one of their products go somewhere else...

As much as I love this country and the people, they are generally brain-dead...which may say something about me...

Steve A.
Last edited by Steve Anderson on Wed Oct 19, 2011 10:08 pm, edited 1 time in total.
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Postby gary » Wed Oct 19, 2011 10:07 pm

Hi Steve,

Panrock wrote:what I would call frame phasing..
Steve O


Indeed, but as we are talking about a cyclical system then phase, or more precisely, phase shift, is an angular quantity.

Panrock wrote:The idea is: now one can turn the thing on and it will run up and lock to line and correct frame phase all at once.


Indeed, the holy grail, that part was clear, but...

Panrock wrote:but I found a mere 10% cut was sufficient to do the job.


... that is not so clear, simply because it seems to me that that would guarantee, if anything, that the framing would be out by 10%, to me that would still need manual intervention. If that is the intention, however, than that's fine, understood.

In addition though, as previously mentioned, I still can't see the need for circuitry to remove sync pulses, unless you envisage using a mechanical camera, as the the two sources of sync pulse stream: the video, and the axis mounted encoder, are both under your control.
gary
 

Postby gary » Wed Oct 19, 2011 10:58 pm

Steve Anderson wrote:Not particularly, probably around the same delivery time, a few days.


A few days! LOL I'm happy with a few weeks - I think my first order from them was in the order of 3 months!

I have communicated with them quite well in the past, I have always, at least received a reply, but if you want to know anything about the item itself, yes forget it, they are just a shipping house really.
gary
 

Postby Panrock » Wed Oct 19, 2011 11:24 pm

gary wrote:
Panrock wrote:but I found a mere 10% cut was sufficient to do the job.


... that is not so clear, simply because it seems to me that that would guarantee, if anything, that the framing would be out by 10%, to me that would still need manual intervention. If that is the intention, however, than that's fine, understood.

That could well be, just as the circuit could lock to 'one line out' when one pulse is missing (as per Klaas' comment further up) - but I don't see why any of this matters.

Wherever the thing is found to actually frame when you first try it, all you are then presented with is a one-off task, namely to set up the position of the sync sensor to whatever position around the 'disc'* results in the picture framing being correct. After that, it should come up right every time.

So any framing differences caused in practice by removing various quantities of pulses are not a problem. As I see it, the only issue is how accurate and repeatable the frame phasing of the 'disc' will prove to be. Personally, I found removing a good chunk of line pulses helped in this regard. No, I don't understand why - but "the proof of the pudding lies in the eating"... :wink:

gary wrote: In addition though, as previously mentioned, I still can't see the need for circuitry to remove sync pulses, unless you envisage using a mechanical camera, as the the two sources of sync pulse stream: the video, and the axis mounted encoder, are both under your control.


Please bear with me - I don't understand the point you are making here . I don't want the sync to be 'under my control' - I want it my mechanical monitor to correctly set this up for itself, both in line and frame, automatically.

Steve O

*or mirror screw or drum...
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