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aapo lettinen

Making new Crystal Sync electronics for CP16R

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I finally got a cheap enough CP16R to start working with my own Crystal Sync update for it. 

The original camera has the only available Crystal speed of either 24fps or 25fps depending on the gears used.  All the other speeds are made with a RC oscillator which is not accurate enough for sync sound work and some of the available speed presets are not very practical.

I am going to make a completely new Crystal Sync system for this camera which allows setting ANY crystal speed from about 10fps to about 40fps in 1/1000fps increments. All speeds crystal and accurate. So one can easily set the camera to all the speeds one likes and one can get 23.976fps as well as 24.000, 25.000 and 29.98fps with the same camera. 

I will update work-in-progress videos on YouTube. You can follow my channel A Lettinen  or this thread for updates. 

The first video where I just briefly opened the camera and tested that the motor itself is working correctly and the mechanics are OK.  I will remove all the original circuit boards and speed selector etc. and will build completely new electronics to the camera. So this update is possible for cameras which have broken original boards as long as the motor itself and the mechanical parts are intact.

Part 1: opening the camera and testing the motor and mechanics

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For what it's worth, I have used the lowish-cost TCXO modules from China and found them to be reasonably accurate, certainly accurate enough for a timecode slate or the like.

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2 hours ago, Phil Rhodes said:

For what it's worth, I have used the lowish-cost TCXO modules from China and found them to be reasonably accurate, certainly accurate enough for a timecode slate or the like.

I like to use basic binary counters and bcd counters when only a couple of easily divided frequencies are needed and if it happens to be beneficial in other ways to. And when a more challenging speed is needed I am using a microcontroller running CTC program based which divides the frequency from the crystal the microcontroller uses for timing, mostly on the hardware level. 

In the case of this CP16R system, I am going to use only microcontroller (ctc) based frequency generation but it makes most sense to use my own software instead of choosing a factory made Chinese module for this. This is because it is easier to build the user interface for the system with minimal parts when I am making everything from ground up. I can eliminate most of the extra parts like additional microcontrollers which communicate with the Chinese module via serial connection. It sounds like it is more work to make everything from ground up but in this case it is beneficial and for me it is even slightly easier than to try to adapt an existing module to work with the system. The frequency generation is pretty easy after all and when building everything by myself I am able to choose all the parts I want to use for every design. Starting from choosing the crystals I will use and in which package every single part comes in :)

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Hi Aapo

I understand what you mean. The TCXO is simply a very low drift clock source for the microcontroller; I've used them with ESP32 and AVR, so these ideas are not mutually exclusive.

 

P

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11 minutes ago, Phil Rhodes said:

Hi Aapo

I understand what you mean. The TCXO is simply a very low drift clock source for the microcontroller; I've used them with ESP32 and AVR, so these ideas are not mutually exclusive.

 

P

oh I though you meant those serial controlled frequency generation modules. 

I use small-ish smd oscillators in some designs (for example one of the earliest designs was based on the Seiko VG-101JA  2.048MHz oscillator divided by binary counters and a bcd counter to frequencies of 125Hz, 160Hz, 250Hz, 320Hz and 500Hz at the same time and an additional 32kHz signal which is used as a sawtooth wave source of a analog PWM circuit) . Due to packaging options and price I am mostly using tht packaged crystals if a very specific frequency is needed (for example 2.4576MHz) or sometimes smd ones if the system is using microcontroller and ctc for frequency generation so I will just need to have some high frequency like 16MHz to work with. Though I like to use tht crystals for 16MHz as well because they are slightly easier to work with. Most of the other parts like all the resistors and capacitors and most of the microcontrollers are smd.

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the issue with most of the tcxo smd oscillators available here is that they are so small that it is challenging to solder them reliably with my tools. By small I mean the whole oscillator being from 2mm to 3.2mm in length and from 1.6mm to 2mm wide with 4 pads to connect to the circuit board. Additionally most models have the operating voltage around 3 to 3.6 volts max. when the 328 or other microcontroller I use needs to run at 5 volts to support the clock frequency of close to 20MHz.  So I have to arrange the around 3 to 3.2V regulator for the oscillator separately and additionally deal with a very small component which is challenging to solder in place (and I need a microscope to verify if it's properly soldered or not) .  So this is why crystals + smd capacitors has been much easier route for me than using smd tcxo oscillators (I have some but no design uses them yet. Some designs use those old Seiko VG-101JA though because one can divide usable frequencies from those directly using only a single binary ripple counter and nothing else)

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About the sound recording system I am developing for this camera. I checked the possibilities yesterday and most likely I will adapt the camera's original Auricon magnetic head to optical recording by removing the magnetic sound heads first and then building my own variable density optical head in place of them. The largest challenge is avoiding spill from the light beam to fog the rest of the film in the chamber so I will need to do lots of prototyping and testing.

The main purpose for optical variable density sound is that one would get a scratch audio track which helps syncing when shooting documentary style material. I will use a external digital recorder for the final recording when making my own projects but a scratch audio track enables storing timecode information or a analog scratch track on the film which enables shooting without clapperboard 1-man band style and helps saving film stock. I have couple of documentary projects which would benefit a lot from this in-camera sound feature.

A person who shoots for direct projecting can use the system for recording the final audio track directly on the film in camera. 

Price range of the optical sound recording feature will be under 1k but will need to make the full prototype first to determine the exact details. I will need to make a compensating system which varies the exposure according to the framerate and the sound quality needs to be reasonably good too. 

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The TCXOs I've experimented with have actually been pretty huge through-hole devices that have sort of the opposite problem; they're enormous by modern standards! That said I do entirely understand your reticence to get involved with too much SMD soldering; I've always avoided it. Smallest thing I ever attempted was some LED character displays which needed sixteen 0402 LEDs per character and four characters per module. It was grim, and I even ordered the solder paste stencil!

HTB1cLiTe8Cw3KVjSZFl763JkFXa4.png_.webp

Temperature-compensated module not absolutely required of course, but if you're going to specifically do a crystal sync module for a camera, I'd say do it.

As to the variable density LED sound exposure, sounds good, but I'd expect lots of experimentation getting things like pre-emphasis right. Wouldn't most people rather use that area for picture if it's in any sense possible?

I might consider doing something that could expose timecode or some other slating information into the first frame of a take.

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1 hour ago, Phil Rhodes said:

The TCXOs I've experimented with have actually been pretty huge through-hole devices that have sort of the opposite problem; they're enormous by modern standards! That said I do entirely understand your reticence to get involved with too much SMD soldering; I've always avoided it. Smallest thing I ever attempted was some LED character displays which needed sixteen 0402 LEDs per character and four characters per module. It was grim, and I even ordered the solder paste stencil!

 

Temperature-compensated module not absolutely required of course, but if you're going to specifically do a crystal sync module for a camera, I'd say do it.

As to the variable density LED sound exposure, sounds good, but I'd expect lots of experimentation getting things like pre-emphasis right. Wouldn't most people rather use that area for picture if it's in any sense possible?

I might consider doing something that could expose timecode or some other slating information into the first frame of a take.

I actually like SMD soldering. it depends on what kind of footprints you have used for the parts... much nicer if they are "handsoldering" style with slightly longer pads so that one can take advantage of the surface tension of the solder. but most of the oscillator parts are not really meant for hand soldering and are a pain to work with by my opinion.

All the normal crystals I have tested have been able to keep frequency accuracy of the camera accurate by at least 4 decimals so the accuracy of the crystal is better than the mechanical accuracy of an old camera system even if it's properly serviced. So in the most cases it is not necessary to use really accurate oscillators because you won't see any difference at all. Maybe if freezing the camera to -30°C or -40°C but most of the cameras don't work in that range anyway and one rarely sees that kind of conditions anywhere where sync sound shooting is actually needed (too cold for actors and crew)

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Why not a microcontroller with a TCXO reference? The PLL some have will give amazing clock stability and putting an absolute encoder onto the motor will let you know exact speed and position, so you could stop it exactly at a desired point and use a basic closed loop control to where it almost would not matter what is happening, since you can use a basic software feedback loop to hold a desired speed. It'd be easy to also then report errors such as underspeed, no movement, no feedback, or whatever you want.

Even a GPS module for GPS referenced timing isn't a very expensive part and would give extremely good stability at the cost of being possibly overkill for a reference but would be handy if deriving timecode from there.

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4 minutes ago, Selinica Harbinger said:

Even a GPS module for GPS referenced timing isn't a very expensive part and would give extremely good stability at the cost of being possibly overkill for a reference but would be handy if deriving timecode from there.

I actually pondered doing that for the timecode project, but I wanted something that'd work underground or in a big steel-framed building. That's why I went with the TCXO.

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By my opinion it is too much hassle for very little real benefit (at normal temperatures even the lowest quality normal crystals can generate a reference signal which is accurate by 4 decimals and the camera mechanics itself or the phase locking algorithm is not capable of doing any better than 3 decimals. The 4 decimal accuracy is barely detectable by instruments and one would definitely not see the difference in the final image. keep also in mind that the 16-bit ctc used for frequency generation does not divide all frequencies at exact accuracy and the 4th decimal is often a little off for this reason. that can't really be helped because it is mathematically impossible to divide all the frequencies by 5 or 6 decimal accuracy) . I can test how the current crystals behave in high and low temperatures but I am pretty sceptical that a extremely stable and accurate clock is really needed for this application (or atomic clock like the gps referenced system) . It is a marketing point which sounds nice but is it actually more useful? most likely not.

------------

It is, however, possible to wire a tcxo oscillator afterwards in place of the normal crystal if someone really wants it. I will need to add extra components anyway to make the tcxo work correctly with the 328 so I could just make a small additional circuit board which has its own power regulator and other parts, the oscillator and which outputs its signal to the same clock input pin of the controller than a normal crystal would. Then I could outsource the problem of the microscopic parts to the additional circuit board so it is less risky and more fun to assemble the system and I could use different style of parts according to the customer's needs.

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12 minutes ago, aapo lettinen said:

keep also in mind that the 16-bit ctc used for frequency generation does not divide all frequencies at exact accuracy and the 4th decimal is often a little off for this reason. that can't really be helped because it is mathematically impossible to divide all the frequencies by 5 or 6 decimal accuracy

I have a nice little Excel sheet which I use to verify the frequency calculations if needed. Here it is used to calculate the CTC countermatch value between 1/10th frame increments. As you can see one can't get 5 decimal accuracy for every and all speeds, that is mathematically impossible 

50547057972_b14d2f44ea_b.jpg

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Today I removed the main board and some other electronics from my CP16R camera body and briefly tested how a simple DIY video tap could be mounted as well. I decided to remove the original optical sensor from the camera as well because it is easiest for me to just install a simple factory made sensor in place of it. I am trying to use as few original electrical parts as possible so that the update would be compatible with as many different cameras as possible whether the original electronics being in usable condition or not.

50629327537_c34517afe7_b.jpg

50629327752_00f6fa9860_b.jpg

I will need to do a lot of testing with the video tap system to find the best working camera-lens combination. But it is very easy to work with it because the CP16R camera does not need optical modifications for the tap... just correct video camera + lens combination and a suitable support for it. The camera I am using for tests is a Chinese microscope camera which costs about 40 bucks or so. One would probably want a better quality camera to get a usable image in normal lighting conditions. 

50628485128_8ed06f56f1_h.jpg

I will continue with the original plan of making a new Crystal motor control system which has any speed selectable from 10fps to 40fps in 1/1000th fps increments. No display is necessary. I will try to get the shutter parking working and I will test if the 200ft/400ft footage warning could be easily added as well :)  

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As a side note, my camera had pretty OK looking main circuit board from the topside but when I removed it, it was revealed that about half of the board was heavily corroded from the underside and it was totally unusable. 

So no wonder people say these cameras often have broken electronics. I see that this Crystal update is thus a very necessary modification to return the old cameras back to service. 

Mechanically these cameras are pretty great. I have used Arriflex 16BL in the past and from the outside it is somewhat similar looking system but the CP16R is clearly a way better camera, especially the noise levels and the lens mount are way way better. And the video tap installation is very easy because it needs very little modifications to install.

I am probably going to update the lens mount to B4 mount because I have a great Fujinon zoom I can use with it. It seems to be pretty hard to find any native CP16 mount lenses or lens adapters from web but the B4 mount will be a much better choice for me anyway and it is way less machining work than fitting a PL mount to this camera model. 

For the viewfinder, I don't know. The original finders are pretty expensive on eBay so it is possible that I could even make my own viewfinder system to it :D 

 

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