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Traffic light signal


Himanshu Choudhary

This project describes the functioning of the traffic light system, which are commonly used on the streets. In this circuit 555 timer is used to produce a clock pulses, which are used by a counter to produce the required output.

Shown below is the pin diagram of a standard 555 timer:

IC 555




In the circuit of this project, 555 is used in astable mode with a variable resistor VR1 (1M) connected between pin7 and pin2. R1 is 100K and C2 is 10uF. The capacitor C1 is used to remove ripples if present from DC source. The other pins of 555 are connected as usual in astable mode. The output frequency is taken on the clock pin of counter IC 4017. Enable pin of 4017 is connected to ground.  The reset pin is connected to C3 and R6 which are connected to VCC and ground respectively as shown in the figure. This is done to ensure that IC4017 resets when switch is turn on. Pins 1,5,6,9 are connected to green LED, while pins 10 &11 are connected to yellow LED. The carry out pin 12, is connected to red LED. The duration of the sequence can be adjusted from 7.5 seconds to 2.5 min by varying the 1M preset. The circuit operates at a 9V DC source.



Circuit Diagram


Resistor Image

Resistor is a passive component used to control current in a circuit. Its resistance is given by the ratio of voltage applied across its terminals to the current passing through it. Thus a particular value of resistor, for fixed voltage, limits the current through it. They are omnipresent in electronic circuits.

Capacitor image

Capacitor is a passive component used to store charge. The charge (q) stored in a capacitor is the product of its capacitance (C) value and the voltage (V) applied to it. Capacitors offer infinite reactance to zero frequency so they are used for blocking DC components or bypassing the AC signals. The capacitor undergoes through a recursive cycle of charging and discharging in AC circuits where the voltage and curre...

LEDs | Light Emitting Diode
Light emitting diodes (LEDs) are semiconductor light sources. The light emitted...
Presets | Variable Resistors
A preset is a three legged electronic component which can be made to offer varying resistance in a circuit. The resistance is varied by adjusting the rotary control over it. The adjustment can be done by using a small screw driver or...
555 Timer | IC 555 | NE555
555 Timer IC

555 is a very commonly used IC for generating accurate timing pulses. It is an 8pin timer IC and has mainly two modes of operation: monostable and astable. In monostable mode time delay of the pulses can be precisely controlled by an external resistor and a capacitor whereas in astable mode the frequency & duty cycle are controlled by two external resistors and a...

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