The film is pulled along two rails by a pin that rises from beneath. The pin is the end of spring that is driven by a solenoid. Since the pin cannot perfectly rise through a sprocket hole each try I have also placed a copper tab above the film so that when the pin hits the tab we will see a closed circuit that indicates that the pin is home and ready to pull the film. If the pin is not home we can try again by adjusting the pin position or re-firing the solenoid. The plastic rails were taken from a windshield wiper blade. The film slides through easily but there is a bit too much play. I t would be better to build rails from metal sheets so that the fit would not allow the film to shift side to side. Maybe next time! The system works well enough that I can connect it to my computer to see how it really performs under computer control.
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