This is a project of a traffic light circuit. The circuit is using a CD4017 IC and few discrete components. CD4017 is a 16 pin DIP CMOS decade counter IC, the clock input pin 14 of the IC controls all the 10 outputs of the chip. When the IC receives a positive pulse on the clock input pin, it goes in to the
internal counter circuit of the chip and activates a single output and deactivates it on another pulse and activates the next.

A multivibrator circuit built with three transistors is used to generate positive pulses. The output pins 1, 5, 6, 9 are connected with a green LED, Pin 10 and 11 are connected with a yellow LED and pin 12 is connected with a red LED. The reset pin 15 is used to continuously reset the IC and repeat the process.

The 390 ohms current limiting resistor is used with each LED to operate them smoothly. All the diodes in the circuit are 1N4148, these diodes are used to save the circuit from short circuits. The time delay of the LEDs can be controlled by the 100K variable resistor. The operating voltage of the circuit is 9 to 12V DC.  

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Traffic Light Project Circuit Diagram