4017 Decade Counter

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4017 pin-out 2


Fig 1 4017 Pin-out


The 4017 decade counter is a highly versatile device.  It counts positive going edges on the ‘clock’ input and stores the result.  The value of the stored count is presented at the ‘decoded’ outputs O0 – O9.  The outputs are normally low except for the output that corresponds to the stored count.  On the tenth count, ‘carry’ changes from low to high and the counter resets to 0.  Carry provides a facility for counting larger numbers; it should be connected to the clock input of the next stage (or digit).


For normal operation, ‘inhibit’ should be held low; making it high stops the counter responding to clock pulses. ‘Reset’ should be held low; making it high resets the counter to 0. At power switch-on, the counter may store a random number.  To ensure a zero count, a power-up reset circuit is required (fig 2). +V is the power supply to the whole circuit controlled by SW1. When SW1 is closed, the output to the 4017 reset pin goes high (because C1 is discharged). After a time period (set by R1 x C1) the reset signal decays to a low allowing normal operation of the counter.


Fig 2 Power-up reset circuit


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