22 February 2013



In the circuit of this project, 555 is used in as table mode with a variable resistor VR1 (1Mohms) connected between pin7 and pin2. R1 is 100KOhms 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 as table 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 1Mohms preset. The circuit operates at a 9V DC source.

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.

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