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VTR_CLOCK

2017-01-08 10:08  
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VTR_CLOCK
Locked oscillator using only two-input NAND gate and 555 timer provides logic clock signal for videotape recorder. Vertical sync signal, stripped from video information re corded on tape, is used as control signal. C1 controls locking range forfree running trequency of 555. When C2 is charging (555 output is high), R2 and D1 determine time constant T1. During discharge of C2, D1 is reverse-biased and discharge time constant T2 is determined by R3 and R4. -L. Saunders, Locked Oscillator Uses a 555 Timer, EDN Magazine, June 20, 1975, p 114.