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:
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.
Filed Under: 555 Timers, Electronic Projects