4017 Counter

4017 Chip IC Pinout

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 Q0 to Q9 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.

A quick glance of the animated timing diagram in the banner section of this page 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, for a decade counter.

Pin 13 is CLOCK INHIBIT; however, confusingly sometimes they also call it CLOCK ENABLE, and sometimes simply "CE" with a line above it. However, whatever they decide to call it, pin 13 must be low for the counter to work.

Circuit

Internal Circuit

GCSE students usually need to know how a 4017 decade counter works, and in particular, the pin functions. Luckily, they are simple to understand.

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.

If we look at the RESET pin 15, we see that it connects to the reset function of the five internal flip-flops, therefore, when pin 15 goes high, the count resets, and starts from the beginning.

Fun Tutorial – Application 1

Application 1

Just for fun, let us play a prank on this poor unsuspecting IC chip. Connect one of the output pins, say pin 1, which represents a count of 5, and connect it to the RESET pin 15.

What happens here is that when the counter counts to five, the high output (logic 1) at pin 1, makes the RESET pin go high, therefore the counter resets itself and begins the count again. Therefore, it keeps repeating this, resetting itself at the count of five. If you had LEDs connected to the outputs, you would see LEDs 1, 2, 3, 4, and 5 lighting consecutively. On the fifth count (LED 5), it would reset and begin the count again. Therefore LEDs 6, 7, 8, 9 would never light because it resets at five.

Just for Fun – Application 2

Application 2

Just for fun, what would happen if we were now to connect pin 1, which represents a count of five, to pin 13. Remember that when pin 13 goes high, it stops receiving the clock pulse. Then in this case, the count simply stops at five.

GCSE

I know how it works in education. You get this over excited Physics teacher, who builds a crows-nest of a circuit with wires everywhere. If you are lucky, you then see a bunch of red blinking LEDs. In the excitement of him patting himself on his back for finally making something in his adult life that works, the lesson is over, and the most important thing you need to know for the exams is never covered! You see, I had that very same Physics teacher :-)

We know that the LEDs blink in the following manner.

  • Succession
  • Progression
  • Consecutively
  • One after the other

However, the most important thing to understand is how the Clock INHIBIT and RESET pins work. How would you implement them? How would you use them? The following pages of this multi-page article continues showing how a 4017 decade counter works.

This Article Continues...

4017 Counter
4017 Counter How Clock INHIBIT Pin Works
4017 Counter How RESET Pin Works
4017 LED Warning Light