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4017 Decade Counter

A 4017 integrated circuit is able to light LEDs up in sequence. A 4017 counter lights up each LED in term every time a pulse is applied to the clock input. The clock input on the circuit symbol is the > sign.

 

The counter can be reset to zero by connecting applying a pulse to the “R” input (Reset).

 

The “EN” input stands for enable. For the circuit to count this must be connected to 0V.

4017 Decade Counter - counts every time the count switch is pressed

How the switches work

 

The reset and clock inputs are normally low because they are connected to the 0V rail via resistors R1 and R2.

 

When a switch is pressed a direct connection is made between the input and +V therefore forcing it high.

 

Every time SW1 is pressed the next LED is lit.

Switch Bounce

 

In reality this circuit may not work properly because of “switch bounce”. This is when a switch produces more than one pulse when it has been pressed because it is a mechanical device. This can cause the counter to count more than one pulse even though the switch has only been pressed once. To find out how to avoid this look on the main page of this site under the heading: Debouncing.

Self Counting Decade Counter

The circuit below shows a 555 astable and a 4017 decade counter. The output of the astable circuit is connected to the clock input of the 4017. The astable circuit produces continuous stream of pulses, each one making the counter increase by one. Each LED will light up in turn before starting again from the start.

A circuit like this can be used in producing displays.