Electro-Optical Products Corp. (New York, NY)has introduced the Model CH-62 Optical Chopper/Shutter, a low cost variable low frequency device (DC to 25Hz) that consists of a blade mounted on a motor with a limited rotation angle. Current in one direction will set the chopper to the open position and current in the other direction will set the chopper to the close position. Using our DCH-62 driver with the “MODE” selector switch provides two modes of operation for the CH-62 chopper/shutter. In the internal mode the CH-62 is used as a variable low frequency chopper. The chopping frequency is set by an internal oscillator adjustable from 1 Hz to 25 Hz. In the external mode the CH-62 is used as a chopper or as a shutter and is controlled by an external TTL signal input. “High” input keeps the CH-62 open, “Low” input keeps it closed. Response time is 10 msec. Maximum frequency for TTL input is 25Hz.