Crystal Sync - How to control camera servo speed?

Post by **reflex** » Tue Oct 19, 2004 4:53 am

In my real life I design consumer widgets based upon microcontrollers. It doesn't seem like a crystal sync setup is very challenging with modern (low cost) "smart" technology. I'm hoping someone can answer a few technical questions about how the sync unit typically adjusts the speed of the cam's film drive motor.

So, in a "black box" scenaro -- one connects the camera's flash output to the sync box, which times the pulses to determine if the motor is running slow or fast, and to what degree. The $500 sync boxes advertised on the web have a second connection back to the camera, which is used to tweak some sort of servo return signal to the motor circuit.

Can anyone provide the gory technical details? I'd love to hack together a design based upon a cheap and cheery microcontroller-based setup. It'd be nice to be able to offer it as an affordable DIY kit with a circuit board and pre-programmed parts.

Cheers, James

Post by **pbrstreetgang** » Wed Oct 20, 2004 12:32 am

http://www.24fps.com might be able to help with answering your techo questions on crystal sync. if you can make a cheap alternative, i'll buy it.

a...

Post by **reflex** » Wed Oct 20, 2004 12:54 am

Thanks - I'll take a look at the link tonight.

I think I'm going to focus on my beaulieu 4008 first -- looks like the speed control is analog, which is a fairly easy hack (if one ignores the oddball 7.2V circuit, which is a pain to interface to modern 3.3/5V controllers).

I'll start by building a microcontroller-based frame counter/timer and take it from there. I'll post my progress!

Cheers, James

Post by **chz160** » Sat Dec 04, 2004 2:14 pm

Reflex, had any luck with that beaulieu hack yet? I have a beaulieu 4008 as well and I'm trying to do the same thing. I'd love to know if you've come up with any ideas.

Later,
Noah P.

Post by **danpuddick** » Sat Dec 04, 2004 2:45 pm

I've been thinking about this too after getting inside my Nizo for the first time. I hadn't really figured out how the bit determining whether the camera was running to fast or too slow would work.

But as regards controlling the speed of the camera - for the Nizo the motor speed selection works by basically selecting a different set of resistors - so you could just bypass the resistor in the camera for your own Microprocessor controlled varible one to keep the speed constant. Maybe there's more to it but it seems that it could work.

Post by **mattias** » Sat Dec 04, 2004 8:01 pm

danpuddick wrote:I hadn't really figured out how the bit determining whether the camera was running to fast or too slow would work.

phase locked loop? i don't quite see the need for a microcontroller. if i only knew how to adjust the camera speed i'm sure i could build a very cheap controller too without much trouble.

/matt

Post by **reflex** » Sat Dec 04, 2004 8:18 pm

mattias wrote:
danpuddick wrote:I hadn't really figured out how the bit determining whether the camera was running to fast or too slow would work.
phase locked loop? i don't quite see the need for a microcontroller. if i only knew how to adjust the camera speed i'm sure i could build a very cheap controller too without much trouble.

The advantage of microcontrollers is that they're REALLY cheap now (as in EUR 3 each) with low part counts for the board, and you can program them to behave intelligently to speed changes. Its also a piece of cake to switch them to run at different speeds (as long as you choose your base clock speed carefully).

Post by **mattias** » Sat Dec 04, 2004 8:27 pm

valid points. can complete "one chip computers" with oscillator, memory and so on be had for that little too? i'm a software guy myself, so being able to program the unit's behaviour without having to mess with the elctronics would be great.

/matt

Post by **ccortez** » Sat Dec 04, 2004 8:35 pm

I'm sure such a thing is available w/programmable firmware.

I wouldn't want to trust a sync sound shoot to my own C++ memory management code tho! 8O

Post by **stoney** » Sat Dec 04, 2004 10:16 pm

I was thinking of building a simple circuit with a list
of materials that people could easily obtain and build.
These solutions are more complicated. The first link
has some very clear and good background material which
helps you understand what and how you would control the
speed of a DC motor. The second link is an actual working
solution. His documentation is great.

As soon as the material in the first link seems to be too much,
skip to the second link.

1. http://www.hitex.co.uk/c166/pidex.html
2. http://www.interq.or.jp/japan/se-inoue/e_pic6_9.htm

If you want to ensure that you have no time left for shooting
film; read this link

homepages.which.net/~paul.hills/SpeedCo ... sBody.html

Stoney

Post by **mattias** » Sun Dec 05, 2004 1:02 pm

stoney wrote:how you would control the
speed of a DC motor.

that's trivial, but super 8 cameras already have speed controls that i'm guessing you would have to interface with, or do you think you can easily replace them with your own?

/matt

Post by **reflex** » Sun Dec 05, 2004 8:17 pm

mattias wrote:valid points. can complete "one chip computers" with oscillator, memory and so on be had for that little too? i'm a software guy myself, so being able to program the unit's behaviour without having to mess with the elctronics would be great.

Sure - check out the Microchip PIC18F1220 - $2.78 in quantities of 100. The only trouble with the on-chip RC oscillator networks is that they're only accurate to +/-1%. Still, a decent precision osc will only set you back about $1.50. The 18F220 has some decent A/D ciruitry built in, although a high voltage solid state relay circuit would be needed to handle anything out of the 3v-5v range.

I've already got a PIC based dev board running from a PC Flash output to give filmspeed readings, and I'm waiting for a cheap cam to arrive from ebay.de so I can test the speed control side of things without risking a good cam.

cheers, reflex

Post by **stoney** » Sun Dec 05, 2004 9:01 pm

Mattias,

You are correct. Every camera is built differently. How do you get
feedback on how fast the motor is actually rotating?

I was going to design a reference signal using a crystal oscillator
and then divide that down using a counter with a fps input. I was
going to use a PLL to generate a voltage error signal to change the
voltage output to the DC motor. The most difficult part is designing
the feedback mechanism. Would I be able to get feedback off of
the shaft? Camera's come in many different sizes with different
motors. If it was easy, somebody would have come up with a
generic solution already.

Stoney

Post by **Nigel** » Sun Dec 05, 2004 9:16 pm

I thought the "Generic" solution was from The FIlm Group??

This is all very interesting I am looking forward to what you design. To bad my 4008 is already Xtal controled.

Good Luck

Filmshooting

Crystal Sync - How to control camera servo speed?

Crystal Sync - How to control camera servo speed?

abend

I was thinking of something simpler, but

Re: I was thinking of something simpler, but

Hardest part is feedback from motor