Four Way Traffic Light Circuit

Introduction

The four-way traffic light circuit is a practical electronics project designed to control the flow of traffic at a four-way intersection. It simulates the operation of standard traffic lights, providing a safe and systematic way to manage vehicular movement in all four directions. The circuit typically uses a combination of timing ICs and decade counters to sequence the lights for each direction—north-south and east-west—ensuring that red, yellow, and green signals are displayed in the correct order. Powered by a simple DC supply, this circuit is an excellent project for hobbyists and students to understand the basics of traffic control systems, digital electronics, and sequential logic. It also demonstrates how electronic components such as the 555 timer IC and CD4017 decade counter can be used in real-world applications. Easy to assemble and cost-effective, this project offers a hands-on learning experience in both electronics and traffic engineering.

Components Required

S.No	Component Name	Value	Qty
1	Resistor	1kΩ	1
2	Resistor	10kΩ	1
3	Resistor	220Ω	3
4	Capacitor	100µF, 25V	1
5	Capacitor	10µF, 25V	1
6	Diode	1N4007	8
7	IC	NE555 Timer	1
8	IC	CD4017 Decade Counter	1
9	LED	Red	4
10	LED	Yellow	4
11	LED	Green	4
12	Power Supply	9V DC Battery	1

CD4017 Pinout

NE555 Pinout

Circuit Diagram

Key Components:

• NE555 Timer IC: Works in astable mode to generate clock pulses.
• CD4017 Decade Counter IC: Takes clock pulses and activates its output pins sequentially.
• Diodes (1N4007): Direct current to specific traffic lights.
• LEDs (Red, Yellow, Green): Represent the traffic lights.
• Resistors & Capacitors: Set timing and protect components.
• Power Supply: 9V DC battery.

🧠 How It Works:

1. Pulse Generator (555 Timer in Astable Mode):

• The NE555 timer is configured as an astable multivibrator.
• It generates continuous clock pulses.
• Frequency depends on R1 (1kΩ), R2 (10kΩ), C1 (10µF).
• These pulses are sent to the CLK (pin 14) of the CD4017 counter.

2. Decade Counter (CD4017):

• CD4017 is a decade counter with 10 outputs (Q0 to Q9).
• On each clock pulse, one output goes HIGH in sequence.
• Only one output is HIGH at a time, others are LOW.

3. Controlling the Traffic Lights:

• The outputs from Q0 to Q8 control the LEDs (traffic lights) via diodes (D1 to D8).
• Each pair of outputs manages the lights for one direction (N/S or E/W).
• For example:
  • Q0-Q3 manage North-South lights:
    • Q0: Green (N/S)
    • Q1: Yellow (N/S)
    • Q2: Red (E/W)
  • Q4-Q7 manage East-West lights:
    • Q4: Green (E/W)
    • Q5: Yellow (E/W)
    • Q6: Red (N/S)
• Each LED is connected through a current-limiting resistor (R3, R4, R5 = 220Ω).

4. LEDs & Diodes Logic:

• Diodes direct specific output signals to the correct LED group.
• This ensures only the correct LEDs light up for each direction at the right time.

5. Reset Pin (MR – Pin 15):

• Resets the counter to Q0 after Q8.
• Ensures the cycle restarts in a loop.

🔄 Traffic Light Sequence Summary:

1. North-South GREEN ON → East-West RED
2. North-South YELLOW ON → East-West RED
3. North-South RED → East-West GREEN ON
4. North-South RED → East-West YELLOW ON
5. Loop repeats.

Notes:

• You can adjust the delay by changing R1, R2, C1 values.
• This is a basic educational model, real traffic systems are more complex with microcontroller logic.

Applications

• Traffic intersection control
• Educational and academic projects
• Simulation of real-world systems
• Embedded systems learning
• Mini project for electronics students
• Prototype for smart traffic systems
• Low-cost traffic management solutions
• Hobby electronics projects