V_F_CONVERTER

Published:2009/7/15 4:49:00 Author:Jessie | From:SeekIC

Can be used with any frequency counter. Only last three digits of display are read for voltage. VCO U22 runs at 1000 Hz when input is grounded and R3 is 56K. Counter is preset to 9000. For OV, count starts from 9000 and goes up to 10,000 on display, except that 1 at left overflows so reading is 0 V. If input is + 1 V, U22 goes upto 2000 Hz, appearing as 1000 on display. Voltage divider ahead of input is needed to divide full-scale voltages of 10, 100, and 1000 V down to basic 0-1 V range. Range switch is wired to place decimal in appropriate position. Use 2.7K for R2. DC voltages are in circles; upper value is for input probe of electronic voltmeter on +12 V, and lower value for input probe grounded. Terminal A goes to over range and reverse polarity indicators using 5558 dual opamp U23 and Archer (Radio Shack) 276-041 or equivalent LEDs. R4 and R5 depend on input-signal excursion range and exact value of sup-ply; start with 2700 ohms for R4 and 18K for R5.-J. Hall and C. Watts, Learning to Work with Integrated Circuits, QST, June 1976, p 20-24; revised circuit in June 1977, p 20-21.



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