How does one implement a frame-counter on a Christie P35GPS? I need to count frames per second, so I need a signal from the projector that tells me when each frame (or sprocket-hole) passes. I'll use this signal to drive a microcontroller counter of my own design.

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"One man can make a difference."

(Naturally, presuming you are using 4 perf per frame film)

When I get to the office I can give you the manufacture and part number.

BTW, This Reel-end Alarm unit has a digital remaining time display for both projectors and when 3 minutes are left on the outgoing reel, a warning is sounded. What is so nice about it, as opposed to the old mechanical bell warning, is that it has an RS32 output so that you can put other readout modules in a remote locations as needed, such as in the rewind room. Very neat unit.

All the above are good suggestions. There are a myriad of ways of getting an input but the three basic methods would be a magnetic sensor, an optical sensor and a shaft encoder. The exact method would depend on what you have available to you as far as parts and tools. I have done it three different ways on the Simplex.

1. Drilled holes and installed cylindrical magnets on a pulley so that one magnet when by for every frame and counted then with a Hall effect sensor. Allergo makes a large selection of sensors.
2. Made a steel pulley to replaced one of the aluminum pulleys and then used a proximity sensor from an old failsafe to count the teeth.
3. Printed a circle with alternating dark and light bands on a piece of Mylar, mounted the Mylar to a piece of Plexiglas and then mounted the Plexiglas to a pulley and used and optical sensor to read the dark bands as they went by. This is a home made optical encoder.
4. Mounted an optical encoder off one of the pulleys and used it to count.

One thing I might try that would require very little mechanical modifications would be to mount a light sensor behind the shutter and see if you can count the shutter going by. It will probably require a litle bit of signal conditioning but it will be easy to install on the projector.

Good luck

Perhaps I could bolt a hall-effect sensor to the shutter...

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What is your purpose in counting the frames? If you are trying to determine FPS then you can put a common tachometer on the motor shaft. That is the way we set the FPS using a variable speed motor on a standard projector.

You can determine the proper shaft rotation by dividing 24 into the nominal speed of the driving motor at sound speed. 1750/24= revolutions per frame. motor rpm/frames per second = revolutions per frame.

The determination of actual frames through the aperture is quite another matter.

I have optical shaft encoders on my projectors.
That takes a bi phase impulse to my mag and digital
reproducers and frame/footage counter.