Three motor cine projector reversible drive - has thyristor switching to gate motor and lamp to protect film and preserve loops at reverse

摘要

The control circuitry is for a reversible drive cine projector. Signals from the spool motors are relayed to the film gate drive motor and the projector lamp so that their operation is co-ordinated, and the film loops preserved plus lamp switched off, to prevent film damage mechanically or by heat. A thyristor (BRX 44) is used when the spool motors are stationary to control the current to the film gate motor (109) via a transistor (107). The transistor (107) acts as a switch for the gate motor (109) and is controlled by a base connection to a preceding transistor (105) from the thyristor (BRX 44). The thyristor (BRX 44) is also used to control the projection lamp (103) so that when the projector main switch is set to a project position, the thyristor is open circuit to the reference rail (7) and, when correct conditions occur on the AND gate (118), current flows through a diode (104) and relay (101) so that the lamp (103) contact is made (102). No separate control knob is required to switch the lamp on; it is done automatically when the projector is running.