The Bombay Salesian Society’s
DON BOSCO INSTITUTE OF TECHNOLOGY
Department of Mechanical Engineering
MEL401: Industrial Electronics Laboratory
Date: Roll No:
Experiment No. 10: Simple Traffic Light System Using 555 Timers
Aim:
To design and construct a simple traffic light system using two 555 timer ICs to control the sequence of red,
yellow, and green LEDs.
Learning Objective:
To understand the astable operation of the 555 timer IC and its application in generating timed
sequences.
To implement a circuit that controls the timing of LEDs to simulate a traffic light .
Learning Outcome:
Students will be able to design a circuit using 555 timers to create a sequential timing system.
Students will be able to analyze and adjust the timing of the traffic light sequence by modifying
circuit components.
Apparatus:
Equipment Specification Quantity
0-32V/0-2A
Dual/Triple Power Supply 01
0-32V/0-2A
Components:
Components Quantity
555 Timer IC 2
100uF Capacitor 2
100k Resistor 1
47k Resistor 1
390 Ohm Resistor 2
330 Ohm Resistor 1
Red LED 1
Yellow LED 1
Green LED 1
Procedure:
1. Circuit Construction:
Assemble the circuit on the breadboard. (A detailed circuit diagram would be beneficial here, but I
can describe the connections).
555 Timer 1 (Master Timer):
Configure the first 555 timer in astable mode.
Use the 100k resistor, the 47k resistor, and one 100uF capacitor to set the timing for the overall
traffic light cycle.
Connect the output of the first 555 timer (pin 3) to the trigger input (pin 2) of the second 555 timer.
555 Timer 2 (Slave Timer/LED Control):
Configure the second 555 timer in astable mode.
Use the 390-ohm resistors, the 330-ohm resistor, and the other 100uF capacitor to set the timing for
how long each light stays on.
Connect the output of the second 555 timer (pin 3) to a simple switching circuit (this part requires
additional components like transistors, which are not in your list, or you can use a simpler method,
explained below).
LED Connections (Simplified):
Since you don't have transistors, we'll simplify the LED control. This setup won't have the classic
"all lights off" in between.
Connect the Red LED, Yellow LED, and Green LED in series with their respective resistors (you'll
need to decide which resistor value goes with which LED to get similar brightness - 390 Ohms for
Red and Green, 330 Ohms for Yellow is a reasonable starting point)
Connect this series LED circuit to the output of the second 555 timer through a suitable resistor to
limit the current. You might need to experiment with the value of this resistor.
The LEDs will likely "dimly light" when they are supposed to be off in this simplified setup.
2. Powering the Circuit:
Connect the positive terminal of the power supply to the Vcc (pin 8) of both 555 timer ICs.
Connect the negative terminal of the power supply to the ground (pin 1) of both 555 timer ICs.
3. Timing Adjustment:
Carefully adjust the resistor and capacitor values in the 555 timer circuits to achieve the desired
timing for each light.
You'll primarily adjust the resistors to fine-tune the timing.
4. Observation:
Observe the sequence of the LEDs.
Note the duration for which each LED is lit.
Measure the voltage at the output of each 555 timer using a multimeter (optional).
Precautions:
Ensure correct polarity of the LEDs and electrolytic capacitors.
Do not exceed the voltage ratings of the components.
Double-check all connections before applying power.
Be careful when handling electronic components to avoid static discharge .
Observation:
Conclusion:
