FOUR_DIGIT_COUNTER

Published:2009/7/12 23:14:00 Author:May | From:SeekIC

A general-purpose four-digit counter can be made from a 74C925 IC and a few external components. That IC contains the counter, multiplexer, and seven-segment digit drivers, all in one convenient package. A couple of important notes about the circuit: The seven 220-Ω resistors (R1 to R7) are used as dropping resistors between the driver outputs and the segments of the display to protect the LEDs and keep the 74C925 from overheating. The four 2N3904 transistors (Q2 to Q5) act as amplifiers for the digital drivers to keep the display at full illumination. Switches S1 and 52, for reset and latch, respectively, are not crucial, but are highly recommended. The latch will freeze the count if needed. If the switches are not used, pin 12 needs to go to ground, and pin 5 to +V (the circuit's voltage supply). If more than four digits are needed, use the MM74C9261C. The functions are the same, but it has a carry out to cascade more than one chip and four-digit display.



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