An important application of fiber optics to data processing is to illuminate hole positions of punched-card reading-stations. In the IBM 59 Card Verifier, flexible incoherently oriented bundles are employed to provide a reliable, efficient, and practical method of sensing holes in punched cards. A phototransistor detects the light coming through open holes and then operates a reed relay directly. In addition, a mechanical light chopper also uses fiber optical components to provide light pulses for the electronic clock to time the machine. An electronic circuit is used to latch reed relays so that the useful signal is digital, rather than the analog hole-to-no-hole light ratio.
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