CALCULATOR_KEYBOARD_ENTRY_

Published:2009/7/12 21:25:00 Author:May | From:SeekIC

Sampling of signals from inexpensive pocket calculator gives complete data entry system for frequency synthesizer or other application requiring BCD input. Circuit includes contact bounce suppression. Automatic constant feature of TI 1256 calculator used permits storing 0.015 as fixed constant, so frequency goes up 15 kHz (channel spacing on 2 meters) each time + key is pressed.Seven-segment signal normally used for calculator display is decoded by programming 74S188 (8223) PROM, using simplified code conversion table given in article. 74175 ICs provide required demultiplexing of segment data. Articl gives construction details.－B .McNair andG Williman,Digital Keyboard Entry System,Ham Radio, Sept,1978,p 92－97.



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