Automatic liquid crystal light-shutter

Claim 1

An automatic liquid crystal light-shutter, comprising: detector means for detecting light and providing an electrical output signal in accordance with said detected light; filter means operably connected with said detector means for blocking signals below a predetermined frequency while passing signals above said predetermined frequency, said predetermined frequency corresponding to the frequency of an alternating welding current supplied by an alternating current electric welding machine and also corresponding to the frequency of the welding spark discharge of said alternating current electrical welding machine; amplifier means operably connected with said filter means for amplifying filtered signals output by said filter means; rectifier means operably connected with said amplifier means for rectifying amplified signals output from said amplifier means; inverter circuit means operably connected with said rectifier means for inverting rectified signals output by said rectifier means; oscillating circuit means operably connected with said inverter circuit means, for providing an oscillating output signal in accordance with one state of a signal input thereto from said inverter circuit means; and a liquid crystal display means operably connected with an output of said oscillating circuit means and operable for respectively blocking or transmitting light in accordance with the presence or absence of an oscillating output signal from said oscillating circuit means.