300_BAUD_BIT_BOFFER_RECEIVER

Published:2009/7/14 7:37:00 Author:May | From:SeekIC

Used with ordinary cassette recorder to convert half sine waves of recorded serial data to corresponding digital 1s and 0s. Output of recorder passes through filter and limiter IC6 to give square wave at point C whose zero crossings correspond to recorded sine wave. Leading and trailing edges of square wave are converted to narrow positive pulses by EXCLUSIVE-OR gate IC4 to give stream of pulses at D, one for each zero crossing. Transistor circuit forms retriggerable mono that is adjusted so point E goes positive three-fourths of way through low-frequency (1200 Hz) half-cycle. Point E then has stream of eight pulses for 0 and no pulses for 1. Final flip-flop provides recovery of data as is and 0s. Leading edge of waveform at D is shortened and combined with clock pulses to provide composite UART clock output. Boffer system eliminates errors commonly encountered when attempting to record square waves on tape with low-cost recorder.-D. Lancaster, TV Typewriter Cookbook, Howard VV. Sams, Indianapolis, IN, 1976, p 167-171.



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