Rotation sensor for a 16mm scanner

Other Hardware Science and Measurement
1

Hi everybody,

after almost six months since I bought my first Arduino and my last post here, I have almost completed the project which is dedicated to scan 16 mm movie film. Here you can see a short video of the old running projector, which has been transformed in telecine machine:

... and here a first test:

I have already increased the data taking frequency, therefore the digitizing speed is higher than the one shown in the video above. However, the speed here is not the main aim of the project: the machine must be stable and then can run during the night.

The reason why I am writing here is to ask a suggestion about a small detail which I would intend to implement. I need to find a way to stop the scanner in an automatic way, once the film is completely digitized.

In the following video, you can see the front film reel:

the reel rotate slowly, stops for a while (when the frame is photographed), then it rotates again, etc. When there is not anymore film on it, the front reel will stop and will not rotate anymore. In that moment the machine can be switched off.

Is there a rotation sensor which can sense the reel when it is not rotating anymore for a long interval (of course the sensor shall not trigger the switching of the machine during the small pause, which is needed to photograph the frame)? It cannot be a sensor which will put too much friction on the rotating axis, otherwise the reel will be blocked. I am searching for a simple solution, because my Arduino is already pretty "busy": I am using it to control three mechanical switches (fast forward, fast reverse, data taking), a TB6600 stepper motor driver, an Hall sensor. Furthermore an output is used to send a trigger to the camera.

Do you have any suggestion for me?

Thank you for your time!

2

Sure! Use an IR sensor in the film path to detect when there is no film. OR use the same to detect the holes in the edge of the film and when the pulses stop, there is no film.
OR build a tachometer for the supply reel and when the delay is more than your limit, the reel is empty and time to stop.
Many possible ways!

1 Like
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Or if there is a spring-arm tensioning the film somewhere, add a switch to detect when the tension is gone.

4

Hi , thanks a lot! I fear that the film could be transparent to IR and therefore an IR sensor would not be suitable. Also there is not a point where I can detect a mechanical tension.

Perhaps a tachometer based on an Hall sensor would be fine. However I have a question:

  1. the axis is rotating for a while (than the angular speed is not null),
  2. then the axis is stopped for a few seconds to take a photo (than the angular speed is null).

How can I do, NOT to stop the switch off the machine, when it is stopping to take a picture?

5

That the film is stopping to take a picture takes x amount of time, right? Add about 20% and then say if stopped longer than xTime +20% then it is really done?

6

Does the take-up reel spin when the film runs out?

Perhaps the spinning of the take-up reel would be easier to measure than the slow turning and eventual stopping of the feed reel.

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