The cardboard projector

The pieces

1. the box A kraft shoebox with a hole punched in one end for the lens tube — light-tight enough to keep the picture from washing out.
2. the lens tube A second, narrower tube telescoped into the front of the box. Slide it to focus the picture on the wall.
3. the film strip Twelve drawings on a paper strip, drawn to cross the lens one at a time as the disc spins — the same twelve frames the shutter disc times.
4. the shutter disc A disc with twelve slots, keyed to the motor shaft. It spins at 68.8 Hz, fast enough that twelve frames a turn blur into one steady picture. Build the same drive, timed to a strobe, at The first movie. Build it on the bench →
5. the motor The motor that turns the shutter disc. Tuned by a 555 timer's strobe on the bench, it settles at 68.8 Hz. Build it at The first movie. Build it on the bench →
6. the bulb The bulb, pulling about 560 mA once it's lit — steady light, so the disc alone does the flickering. Build the same lamp-and-disc drive at A lamp and a disc. Build it on the bench →
7. the battery A 9 V battery, tucked in behind the film strip. Build the circuit that uses it at Ohm's law. Build it on the bench →
8. the switch The slide switch that makes or breaks the 9 V line to the lamp. Build the two-switch version at Series switches. Build it on the bench →
9. the speed knob The knob that sets the strobe's speed — turn it and the flash rate slides from 48.0 Hz to 129.8 Hz. Build the full strobe at The first movie. Build it on the bench →