Is there alternative to Crystal Sync?

[Keith Walters]

I wasn't looking for Keith to insult me or imply I am not capable of eventually creating a phase locked loop. With enough practice and study, I think people can do pretty much anything they want. I just feel like Keith often spends more time telling others what they can't do instead of doing something himself. It's easy to be an armchair naysayer but harder to contribute and do something to show that you yourself are worth your salt.

 

 

I wasn't going to wade in any further into this drivel, but I'm curious; what exactly do you think my background is?

And also what sort of person with an "Engineering Degree" works in an Electronics store?

 

Regarding stepper motors, I actually have one on my workbench right now which is going to power a Home Theatre automatic screen raising and lowering system. Strangely enough, it behaves exactly the way I said it would - 200 biphase clock pulses make it execute exactly one rotation. I have absolutely no idea what you were talking about, and neither do you.

 

"With enough practice and study, I think people can do pretty much anything they want."

Yes, that is exactly, painfully correct; "With enough practice and study, people THINK can do pretty much anything they want..."

 

Like all the imbeciles who think you can get 16 stop DR with a 12-bit ADC, and get abusive when you try to set them straight.

Etc etc.

[Matthew W. Phillips]

I wasn't going to wade in any further into this drivel, but I'm curious; what exactly do you think my background is?

 

I'm sure your background isn't nearly commensurate to your level of arrogance. Then again, I'm sure you'll dispute this.

 

 

And also what sort of person with an "Engineering Degree" works in an Electronics store?

 

He doesn't work in the store, he owns it. He is retired and looks to be even older than you are, Keith (if you can believe that.)

 

Regarding stepper motors, I actually have one on my workbench right now which is going to power a Home Theatre automatic screen raising and lowering system. Strangely enough, it behaves exactly the way I said it would - 200 biphase clock pulses make it execute exactly one rotation. I have absolutely no idea what you were talking about, and neither do you.

 

Yes, I'm aware that 200 * 1.8 degrees = 360 degrees = one rotation. No poop. I don't think you realize what I was saying and it's obvious you don't. I do know what I'm talking about, at least design theorically. Maybe I can help you understand what was in my ind so you can further insult me and entertain yourself. Okay, here goes:

 

What I "originally" had in mind was something like a film projector. You have a motor driving the unit and gears and belts attached to the motor. As you know, you can acheive interesting and variable levels of movement with different assortments of these items. Therefore, if you have a step motor that is n degree steps, you can amplify the relative distance of the step by adding a larger gear. A degree is irrelevant to me in that situation. It's like the Earth...a degree is smaller at the North and South pole but larger at the equator. As such, I can utilize a small axle to have a larger physical rotation. Make sense yet? I may not always explain myself well but I know what I'm talking about. This idea is nothing new.

 

Also, I don;t know where you get the idea that step motors only come in 1.8 degree steps? They are common up to 7.5 and occasionally larger.

 

"With enough practice and study, I think people can do pretty much anything they want."

Yes, that is exactly, painfully correct; "With enough practice and study, people THINK can do pretty much anything they want..."

 

Like all the imbeciles who think you can get 16 stop DR with a 12-bit ADC, and get abusive when you try to set them straight.

 

I know little about electronics NOW but in time I will know a lot, if that is my desire. I knew NOTHING about computer programming when I was 14 and decided I wanted to learn it and have written many programs, from high level Q basic, to mid-level C then C++ programs of varying complexity, to full out ASM modules and bootloaders for small operating systems. Never underestimate the power of the human will when it comes to desire. Every good Cinematographer on this forum started out knowing nothing but had a strong desire to know more.

 

I would be willing to learn from you, Keith, if I thought you had (or willing to share) anything good to offer. But I have seen you on these boards for years behaving the same way to everyone. It's pretty much a joke to people on these forums and other forums that know you. You are the guy who is the windbag that people generally ignore. Sadly, there are individuals like me and even Jim Jannard who give you credulity enough to argue with you.

 

Cheers,

Matthew

[Chris Millar]

I'll wade on in and say that stepper motors run very quietly on the workshop bench but once you mount it your camera the nature of its intermittent action is amplified A LOT though a camera, defeating the purpose somewhat - ok for PIC controlled/programmable 'shutter angle' intervalometers though.

 

I reverse engineered a tobin PLL based Bolex/cyrstal unit once (not fun and near destructive) and built it successfully on a breadboard again - parts prob less than $15...

 

Anyway, even with the wiring diagrams and all the associated part data sheets I gave up trying to actually understand it, part digital/part analog electronics is funky stuff - ODE's and wotnot - you'll learn a lot, but the time investment is large.

 

I studied a BE in mechatronics (mechanical and electronic/electrical combined into a fancy word) for 2.5 years, obviously didn't learn enough related stuff (or I'm a numpty) to nut it out without getting interested in something else and moving on.

 

The frequency that 555's and crystals run on (and combinations thereof) is dependent considerably enough on heat if I recall. Not as spectacularly great as desired once they are held up to the critical nature of many potential applications, they aint the one stop shop that most hobbyist electronics forum users would have them be.

Edited October 6, 2009 by Chris Millar

[John Sprung]

I'll wade on in and say that stepper motors run very quietly on the workshop bench but once you mount it your camera the nature of its intermittent action is amplified A LOT though a camera, defeating the purpose somewhat - ....

 

How much noise steppers make depends a lot on how you drive them. There was a dub stage projector years ago that was all done with steppers -- no geneva intermittent. The pulldown sprocket was driven by a stepper, intermittent at 24 fps, and continuously for high speed forward and reverse, which was considerably quieter than play mode. Its slewing mode was also a lot gentler on the film than the geneva.

 

 

 

-- J.S.

[Chris Millar]

How much noise steppers make depends a lot on how you drive them. There was a dub stage projector years ago that was all done with steppers -- no geneva intermittent. The pulldown sprocket was driven by a stepper, intermittent at 24 fps, and continuously for high speed forward and reverse, which was considerably quieter than play mode. Its slewing mode was also a lot gentler on the film than the geneva.

 

I tried all the methods available to me with my knowledge at the time, half-step, wave, micro-something-or-other etc... I found certain frequencies (speeds) were quieter in different modes - basically when the rate of pulses was such that the stepper motion became continuous, a band of speeds where the momentum of the last step was immediately soaked into the motion of the next step...

 

So I guess yeh sure if you were to design a stepper ground up for an application you could make it, well, perfect ... But as for off the shelf, expect possible coffee grinder sounds - yeh sure, I'm talking Bolex, but boy was it loud, I really thought I had broken something.

 

A projectionist friend showed me a link to a projector based on steppers - maybe the same as you're talking about - Much less oil than a geneva huh :lol:

[Michael Collier]

Your going to have a few issues to deal with Matt, and don't think I am piling on, because if you check my posts I am doing virtually the same thing. I also don't think Keith was out to antagonize you, just point out flaws in a sharp way....in my experience that's what engineers do best. I doubt he was trying to insult you. But here's my (hopefully) constructive criticism with your design so far.

 

First 555 wont do the trick. They stay somewhat stable, but not nearly enough. By your own calculations 36 frames off per mag, and that's under ideal circumstances. As temperature changes, so too will the clock cycle. Though it will stay relatively stable at that new rate, you'd have to trim the timing every time temperature changed.

 

I am not sure why you have such an aversion to crystals. A crystal can cost as little as a dollar, and you can use, as was mentioned, microcontrollers to bring the clock rate down to what you need. Programing a chip to do that would be very simple indeed, and with your programing background it should be easy to either learn the asm language of the chip you plan to use, or to use a C compiler.

 

The problem you will have with steppers is the control. Yes you can add a gear to make the camera advance one frame every step. But conservation of energy tells you that won't be free. If you have a 1.8deg stepper, you need 200 times the torque required to inch the camera to drive it (plus efficiency loss due to the mechanical gearing down). If you have a 7.5deg stepper, you still need 48 times the torque. Finding a stepper with the required power might prove difficult, depending on the action of the camera in question.

 

The next problem is the intermittent start stop cycle of those motors. Every time it advances, all the gears will slap against each other, and when it stops, the play will allow them to hit the other side of the teeth, making 48 distinct pops per second. The volume would be determined by the amount of play, the speed of the motor, and the effort it takes to move one frame. It would be far from silent, and might negate the positives of being somewhat near sync speed, regardless of how silent the motor sounds stand alone on a work bench.

 

.......(tangent I just thought of, given the speed a stepper moves at between steps, wouldn't it be a danger to the film itself? if the stepper moves in milliseconds, the acceleration of the film stock might be too much for it to manage, resulting in the pull down pin breaking or tearing perfs? just a thought)

 

If you move forward, and find a way to resolve the above problems, you should look into upping the frequency to 48hz, and gear the motor to only advance 1/2 frame. If it advanced an entire frame within the time it takes to turn the motor one step, you might find the exposure time is inconsistent and quite short. If you have a signal to open the shutter and another to close and advance, the exposure portion would be more stable. Even better would be to up the frequency 4.8khz and drive a 1.8deg stepper at 24 revs/sec (with a 1:1 drive gearing to the camera's movement) That way there is constant pressure on the gears

 

But I think the best bet would be to use a DC motor with feedback. Its complicated, but its doable. It will also ease wear and tear on gears that were designed for consumer use. They are likely teflon and weak. strong start/stop cycles could reduce the life of your camera. Look into microcontrollers. If you need help getting started I can help, like I said my design works on microcontrollers alone, so I have some experience programming them. You might even be a better programmer than I. You might find a programmer for 12 bucks (like I did), get the company to send you free samples of microcontrollers, which have on board crystal drivers, and get the development environment for free. Net cost, 13 bucks, including the crystal.

 

My project uses everything that people are trying to push on you, and trust me its not the simplest way to go, but the most effective, and not necessarily the most expensive. But crystals, microcontrollers, PLL circuits, and PID control are all very effective techniques to drive a DC motor in perfect phase.

 

BTW, you or someone else mentioned not being able to find a cheap method of determining camera speed. I had extra room on my chip to program in a test tachometer, that now resides on my proto-board. It flashes an LED at a constant speed, and I can look at the disc with the light blockers to see if its in sync or not. If it is, a dot appears to stay rock solid. If not it will drift around the disc one way or another, from which I can determine the exact speed, or reprogram the chip to set a different tach speed. Its ugly, a bit convoluted, but I didn't have to spend anything to determine the stability of my hardware and software. Its helped me solve a bunch of problems anyway.

[Matthew W. Phillips]

I never said anything about a camera! My God, doesn;t anyone listen to everything I say or only the parts to zing me with? I said I was wishing to design a projector but I wanted to add better accuracy than the approx. motor driven ones of the past. I don't know where I said I wanted to make a camera motor?

 

I'm sorry if I seem pissy but this is what happens when people like Keith act condescending without even reading all of my posts.

 

What I "originally" had in mind was something like a film projector. You have a motor driving the unit and gears and belts attached to the motor. As you know, you can acheive interesting and variable levels of movement with different assortments of these items. Therefore, if you have a step motor that is n degree steps, you can amplify the relative distance of the step by adding a larger gear. A degree is irrelevant to me in that situation. It's like the Earth...a degree is smaller at the North and South pole but larger at the equator. As such, I can utilize a small axle to have a larger physical rotation. Make sense yet? I may not always explain myself well but I know what I'm talking about. This idea is nothing new.

[Matthew W. Phillips]

And FYI, I did indeed buy a Crystal Oscillator along with a 74HC390 IC for dividing the frequency. I'll see how that turns out.

[Chris Millar]

I used magnets and a hall effect sensor for my feedback - but encoders are pretty cheap too ...

 

I've opened up a tobin motor (the style for the wind ups as compared to the crystal unit for the EL I previously mentioned)... Clive has built or bought quite a course gauge one with about 20 or so PPR a little IR LED and photodiode part snuggles around the disk and the enclosure keeps it dark enough...

 

Parts = cheap !

 

From memory I think there are crystals in the KHz range and you can divide them up but you have to be aware that some dividers 'divide' simply but removing n pulses every nth pulse leaving behind a kind of bastard variable duty cycle 'oblong' wave... Sure you'll get your counts per second but the distribution within that second is all up the wall... Not sure if this is relevant with uP's or not (?) but if memory serves me well it does a PLL's head in

[Michael Collier]

Sorry. I missed that part about the projector. But if you want to get into electronics, learn to program microcontrollers. Its a good skill to have, and greatly reduces the number of individual parts you have to have on hand to build a project (and increases the complexity possible). Sometimes one crystal, a couple of caps and a chip is all you need. Plus whatever input/output parts are needed (buttons, LEDs, etc)

 

I picked up something like this:

http://www.jdm.homepage.dk/newpic.htm

 

but mine was factory made on greenboard for $12. You could likely make one for 3-5 bucks. then use it to program chips like this:

 

http://www.microchip.com/wwwproducts/Devic...ocName=en010205

 

notice the price is $0.39 in volume, and includes the crystal drive circuit on board. It has flash memory so you can program 100,000 cycles. I have had the same 3 chips in rotation with my prototype programing them sometimes 20 or 30 times in a day and have yet to have one fail.

 

Really nifty little devices.

[Paul Bruening]

I never said anything about a camera! My God, doesn;t anyone listen to everything I say or only the parts to zing me with? I said I was wishing to design a projector but I wanted to add better accuracy than the approx. motor driven ones of the past. I don't know where I said I wanted to make a camera motor?

 

I'm sorry if I seem pissy but this is what happens when people like Keith act condescending without even reading all of my posts.

 

I am definetly sympathetic to your challenge since this is what I hope to solve. I've got one Mitchell head for both telecine into an XL2 for workprints and individual scans for a DSLR. The scans part works just dandy. The telecine doesn't hang with the 23.976 part.

[John Sprung]

From memory I think there are crystals in the KHz range ....

 

Indeed there are. Somewhere in my antique junk, I have one of the very first Eclair crystal add-on boxes. It uses a low frequency crystal like that, and in those days, the cascading divide by two stages were made using discrete transistors. Thirteen stages, IIRC. Today -- well, even 30 years ago -- you can get IC's with more divide by two's than that. IIRC, they go to something like 22 stages?

 

The higher frequency crystals are less expensive and more stable. That's why most modern designs are up in the MHz.

 

 

 

 

-- J.S.

[Matthew W. Phillips]

Indeed there are. Somewhere in my antique junk, I have one of the very first Eclair crystal add-on boxes. It uses a low frequency crystal like that, and in those days, the cascading divide by two stages were made using discrete transistors. Thirteen stages, IIRC. Today -- well, even 30 years ago -- you can get IC's with more divide by two's than that. IIRC, they go to something like 22 stages?

 

The higher frequency crystals are less expensive and more stable. That's why most modern designs are up in the MHz.

 

 

 

 

-- J.S.

 

The store near my house (which is like the only store within 100 miles or more that sells such stuff without going online) has a wide range of frequencies in the MHz range. They don't have any in the kHz range, but since you said what you did, I'm glad I didn't go for the lower frequency anyway. I purchased a 10 MHz and a 24 MHz.

 

So John, do you feel that the 74HC390 is sufficient to divide the frequency of the oscillator stably, or should I use something else?

[Michael Collier]

Looking at the data sheet (from phillips, your brand might be slightly different) The 74HC390 is rated nominally to 28mHz in a wide range of ambient temperatures, but you must supply 6.0v. you can get up to 24mHz at 4.5v, but you probably want to work in some overhead to keep it stable.

[Paul Bruening]

Hey Matthew,

 

Are any ideas gelling up in you?

[Matthew W. Phillips]

Hey Matthew,

 

Are any ideas gelling up in you?

 

I've been practically ADHD lately as far as electronics goes. One minute I'm fascinated with motors, the next with timers, and the next with utilizing LED lighting for something useful. I know this may sound crazy, but I've actually been thinking about trying to group together high luminosity LEDs and channel them to display film on the wall. The key advantage to LEDs over a standard light source, in my mind, it how LEDs have such a small amount of heat generated and it will not burn up the film even if you freeze frame with full lighting capacity. I have experimented with as little as 4 LEDs (rated at 25000 mcd) arranged in a tight square pattern with white reflective material wrapped around and I managed to generate enough light to push an image through the film onto the wall in almost toal darkness. Although that's no where near what I need for average projection, it is encouraging to see a clear image I can make out, even if it takes pitch black to do it!

 

I messed with the 74HC390 and didn't find it what I thought it was. It seems to not be too stable. Then again, maybe I just need to bump up the voltage on it.

[John Sprung]

I've actually been thinking about trying to group together high luminosity LEDs and channel them to display film on the wall.

 

The local True Value Hardware here has an Edison base LED lamp rated at 40 Watts incandescent equivalent for $12. It looks to have about 20 of those blue-white LED's in a small plastic globe. It draws 1.5 Watts, and runs very cool. Sort of a nitelite on steroids.

 

 

 

 

-- J.S.

[Paul Bruening]

I'm excited to hear about your ideas. Funny, I've shared most all of mine, here. I just get jazzed sharing ideas and building on them with the fellas. I know I'm also giving away the parts that might actually be workable. I just don't seem to care. Though, I would recommend to anyone else to hold back the stuff that might actually turn into money for them. I always look forward to the next round of brain anybody can come up with.

[Matthew W. Phillips]

I'm excited to hear about your ideas. Funny, I've shared most all of mine, here. I just get jazzed sharing ideas and building on them with the fellas. I know I'm also giving away the parts that might actually be workable. I just don't seem to care. Though, I would recommend to anyone else to hold back the stuff that might actually turn into money for them. I always look forward to the next round of brain anybody can come up with.

 

I get jazzed about sharing ideas with the group too...at least until I get negative attitudes which, thankfully, are a very small minority. You, John, and Michael have great attitudes and I am always thankfully when you guys chime in to help.