Traffic Light Simulation with 555 Timer and CD4017

Introduction

This experiment simulates a basic traffic light system using a 555 timer to generate a clock signal and a CD4017 decade counter to control the sequence of red, yellow, and green LEDs. The 555 timer provides a pulse, and the CD4017 steps through outputs, lighting the LEDs in sequence to simulate traffic lights.

Objective

The objective of this experiment is to demonstrate how a 555 timer IC and a CD4017 decade counter can be used to simulate a traffic light control system with sequentially changing lights.

Components Needed

1 x CD4017 Decade Counter IC
1 x 555 Timer IC
3 x LEDs (Red, Yellow, Green)
3 x 220Ω Resistors (for LEDs)
2 x Resistors (10kΩ and 1kΩ for the 555 timer circuit)
1 x Capacitor (10µF for the 555 timer)
1 x Breadboard
Connecting Wires
Power Supply (5V)

Circuit Diagram

Procedure

Place the CD4017 IC on the breadboard and connect pin 16 (VCC) to 5V and pin 8 (GND) to ground.
Connect the red LED to the CD4017's Q0 output (pin 3), the yellow LED to the Q1 output (pin 2), and the green LED to the Q2 output (pin 4). Connect the cathode of each LED to ground through a 220Ω resistor.
Set up the 555 timer in astable mode to generate clock pulses:

Connect pin 1 (GND) of the 555 timer to ground and pin 8 (VCC) to 5V.
Connect pin 2 (TRIG) to pin 6 (THRESH).
Place a 10kΩ resistor between pin 7 (DISCH) and VCC, and a 1kΩ resistor between pin 7 (DISCH) and pin 6 (THRESH).
Connect a 10µF capacitor between pin 6 (THRESH) and GND.
Connect pin 3 (output) of the 555 timer to pin 14 (clock input) of the CD4017.

Connect pin 15 (RESET) of the CD4017 to ground to allow the counter to step through all outputs.
Power the circuit. The red LED will light up first, followed by the yellow and green LEDs, simulating a traffic light sequence. The process will continuously repeat.

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Results

When powered on, the LEDs will light in sequence: red, yellow, and green, mimicking a real traffic light system. The timing between changes is determined by the 555 timer, and the CD4017 advances the LEDs based on the clock pulses.

Conclusion

This experiment successfully simulated a simple traffic light system using the 555 timer and CD4017. The 555 timer acts as a clock source, and the CD4017 sequentially switches between outputs, illuminating the red, yellow, and green LEDs to represent a working traffic light model.