The 4017 Decade Counter IC

The 4017 chip is a decade counter providing 10 decoded outputs. Internally, this integrated circuit (IC) chip is a 5-stage divide-by-10 Johnson counter. Sometimes they simply call it a Johnson Counter with ten decoded outputs. The outputs Q1 to Q10 are decoded and in decimal, which means that each output pin represents a decimal count, up to a maximum of 10, and then repeats, hence it is ideal as a decade counter.

The 4017 IC is particularly noteworthy for its simplicity and versatility in creating sequential LED displays, timers, and other applications where sequential counting is required. Its compact design and ease of use make it a favorite among hobbyists and professionals alike.

Pin Description

Pin 16: Vcc – The Vcc pin can be connected to a supply voltage ranges from 3V to 15V.

Pin 8: GND Pin

Pin 13: Enable – It is an active low enable pin. It is usually connected to a logic low voltage which enables the counting. When applied with a high state it inhibits the clock input and stops the counting.

Pin 14: Clock input -The IC counts each rising edge applied to this input by 1.

Pin 15: Reset – It is an active-high reset. It is normally connected to GND or low voltage. If applied with a high state voltage it resets the counter and is set to zero.

Pins 1-7 and 9-11 are the decade outputs

Pin 12: Carry out – A carry out completes its one cycle on every 10 clock input cycles. It is mainly used if the counter needs to be cascaded with any succeeding counter so as to count every 10 counts completed by the first counter.

If we look at the internal circuit of this IC chip, we see that the clock signal (pin 14) goes through a NOT gate, and the output of that then goes into an AND gate with inverted inputs. For this gate to produce an output of logic 1, both of its inputs must be at logic 0, consequently pin 13 must be tied low for the clock signals in pin 14 to get through the gate. So pin 13 simply controls whether the clock signals get through.

A quick glance at this animated timing diagram shows that each pin produces a brief output at successive clock pulses. However, notice that the CLOCK INHIBIT pin has to remain low and the RESET pin has to remain low to create a decade counter, the most common use of a 4017 Oscillator.

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