Question on the 4046

[kareno]

Hi Harry,

I used a very simple 7555 circuit for the motor sync in my Kerplunk scanner and it works well. It is simply a flip flop - set by separated sync, cleared by opto sync. I've found that quality of control is much more dependent on the motor and associated mechanics than the electronics. I knew this scanner was going to be easy to control before I built the electronics - on removal of power it came to a halt in a second or two - always a good sign in my experience.

[Harry Dalek]

Hi Harry,

I used a very simple 7555 circuit for the motor sync in my Kerplunk scanner and it works well. It is simply a flip flop - set by separated sync, cleared by opto sync. I've found that quality of control is much more dependent on the motor and associated mechanics than the electronics. I knew this scanner was going to be easy to control before I built the electronics - on removal of power it came to a halt in a second or two - always a good sign in my experience.

High Karen

Thanks fro the schematic its interesting to know what works ,i have never really tried automatic mechanical television sync ,only on scope tv's in the past ...
I sort of went all out on this one ,i have not been able to try it yet after rebuilding the power supply a different way its playing up i think your idea of simple is best tends to be right .

When i again fix my mistake on the power supply i will try the motor control circuit its more a test bed to see what works ...or not

Experience and that advice is pretty welcome ! so i have taken that in i will check the mechanical side of things as well the opto fork from the little i have played with them i found a little fussy for my past circuit reason i put that schmitt trigger in.

Thanks again Karen i will let you know how it gos least i can try yours if i fail ! any case i will try it more than likly in time good to have another circuit handy ,if mine does work i will post it too.

[AncientBrit]

@ Karen,

Does the 7555 S-R circuit suffer from the false frame lock of the 4046 or is it more reliable in locking?

Regards,

Graham

[kareno]

Hi Graham,

I never aim for line AND frame lock in my monitors. I suppose I feel I should struggle as they did in the era but I only expect my controllers to achieve line lock and then get frame lock by hand.

I confess - I don't know how the club circuit gets so close to frame lock!

Actually, the problem of persuading the images to roll to get frame lock without them taking off and losing control completely is something I've been working on. It might get a mention in the next newsletter so I shan't say any more now

[AncientBrit]

@Karen,

Line and frame lock?. I'll look forward to your article.

Interesting that you mention that sync is easier to achieve where the free-wheeling motor slows down quickly.

I've often wondered whether dynamic braking would improve the performance of the servo rather than our usual method of pulsing power on-off and relying on the natural braking effect of the mechanics.

Regards,

Graham

[kareno]

Hi Graham,

Damping is the energy loss component of a second order system and so lossy mechanics have high damping.

An 'H bridge' drive might help in some cases so that active rather than passive breaking is possible.

[Steve Anderson]

I've often wondered whether dynamic braking would improve the performance of the servo...

Likewise. When and if I ever get around to a mechanical monitor that's what I plan to do assuming the use of a conventional brushed DC motor.

Replace the power MOSFET with a small signal version (say a 2N7000), provide it with some form of resistive load to replicate the gain arrangement of the existing motor drive circuit then follow this with a power op-amp. A TDA2040 springs to mind, it's billed as an audio amplifier, but a power op-amp is all it is. Without referring to the datasheet, I'm not sure it's unity-gain stable though.

Failing that, a pair of complimentary trannies, say TIP29/30s or Darlingtons (TIP140/145) plus suitable bias.

A worthwhile experiment that those who have operational mechanical monitors would be to run it up and achieve sync-lock, disconnect one lead of the motor and time how long it takes to come to a complete stop. Repeat the exercise but this time disconnect the motor and short out its winding(s), note the difference (if any).

If there is any difference in the times then the above push-pull drive may be a valid improvement.

Or perhaps others have tried this before?

Steve A.

P.S. I've just checked the TDA2040 datasheet, it isn't stable at unity gain, but that could be got around...

[Harry Dalek]

Hi just reading the posts on Line and frame lock ,i am pretty new to trying to do this on motor monitors but i don't understand what the problem is on a nipkow what rolls ? or does the picture not center its self even with the sync mmmm ..With holtzmans CDM its very interesting in manual ...due to the stepper motor doing the nbtv horizonal its pretty easy to lock on just manual speed control ,With the Vertical drum is close to lock never real can in manual but the times it does adjusting the speed of the stepper motor really only increases or decreases the picture resolution...sort of zooming in and out a bit but i have really only tried this on test cards so don't know yet if it has the same effect on a moving image .

I was thinking perhaps just because the clubs circuit uses a PLL is the reason the picture is framed right .....MAGIC i think like old tv show catweazle and hes surprise and wonder at the telephone the telling bone , by the sounds of it dealing with what gos on in these ic's is the same to us ?



Karen The reason i am going for a more complex circuit is i want it to do the line and frame locking ...The 4528 seems to have been used a bit reading the newsletters for crt type systems scope tvs i just want to pinch the idea for 2 motor drum control .

I just finished putting my power supply back and testing the monitor with it so back to normal ...i did do a a sync lock test with my circuits clock and it locked right away so i see your 555 timer flip flop would have no problem with the line sync ...So i will be testing fault finding what ever next few days .

[Harry Dalek]

Hi i have just been reading this pdf on photo transistors reading fig 3 what do you think ? As that whats used in the club circuit .

[Steve Anderson]

Harry, He's absolutely correct. Note the chip is a 74LS series, these require a considerable (by today's standards) amount of pull-down current. As he rightly points out the resistor would have to be of a low Ohmic value and the photo-transistor would have to supply 5mA of current when conducting if it were 1k. Depending on the photo-transistor used this may require an amount of light that isn't available.

With a CMOS logic chip, 4000 series, 74HC series and so on, these have for all intents and purposes zero input current, so the resistor can easily be decades greater in value and the photo transistor only need supply a handful of micro-amps.

The Club circuit feeds a CMOS 4011, note the high-value pot to set sensitivity.

Why use LS stuff these days? They guzzle power.

Steve A.

[Harry Dalek]

Harry, He's absolutely correct. Note the chip is a 74LS series, these require a considerable (by today's standards) amount of pull-down current. As he rightly points out the resistor would have to be of a low Ohmic value and the photo-transistor would have to supply 5mA of current when conducting if it were 1k. Depending on the photo-transistor used this may require an amount of light that isn't available.

With a CMOS logic chip, 4000 series, 74HC series and so on, these have for all intents and purposes zero input current, so the resistor can easily be decades greater in value and the photo transistor only need supply a handful of micro-amps.

The Club circuit feeds a CMOS 4011, note the high-value pot to set sensitivity.

Why use LS stuff these days? They guzzle power.

Steve A.

Hi i was wondering if this is a problem ,i notice that club posting still does not have the 4011 between the fork and pll ...so does mean this is the reason every one is having trouble getting it to work right ...i having been reading past postings and seeing corrections ...theres a lot of little changes from circuit to circuit for the same idea ...but never really read which one its the best or right way to go..i sort of choose your circuits when i see them as i know they work ,let you know how the lm311 version go's...just playing around with the opto fork at the moment .