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CD4017B Decade Counter Chip

On the rising edge of the clock pulse, the next output goes high (moving left to right in the diagram below).
At any time, only ONE output is high.

Data Sheet from Texas Instruments

• The yellow numbered pins are the outputs from 0 to 9.
• Only one output is high at any given moment.
• On the rising edge of the clock pulse, the counter is advanced by one if CI is low.
• MR is the Master Reset to reset the whole chip. The output is reset to zero and pin three becomes high.
• CP is the clock pulse input.
• CI is the clock inhibit input.
• If CI is high, the counter stops counting but is not reset.
• If more than one counter chip is being used, the O output can be used to clock the next chip.
• The chip can drive LEDs with about 4 mA flowing. In a 5 Volt circuit, use 680Ω current limiting resistors.

A Circuit with Reset

View this circuit in the Lushprojects Simulator. The simulation differs from real life because an extra NOT gate is needed.

Here is the correct circuit diagram for the 4017 chip without the NOT gate.

Count from 0 to 5, Reset on 6

This counter will count to five. When it hits six, the reset pin goes high and microseconds later the counter has reset. The reset is so fast that no human could ever see it reaching six.

Counter with reset and OR Gates

As this counter goes from 0 to 9, the buzzer will sound when it reaches 0, 2, 4 and 6. This will give four beeps with a short pause before repeating.

If the reset switch is held down, the counter will reset to zero. Pin 0 will be high so the buzzer will sound as long as the reset switch is held down.

Traffic Lights

The diodes act as OR Gates. If pin 9 is high, following the wires with doides, the left amber light will be shining and the right hand red and amber lights also.

Drivers are Needed

Real world traffic lights are bright and need much more current than this chip can provide. MOSFET switch driver circuits can be placed between the counter chip and the traffic lights.