Hi Mentees! we hope you are doing great. Welcome to a super easy yet useful project based upon the simulation in Proteus. We are working on the Traffic Lights project that will work with the help of D Flip Flop. In this simple tutorial, you will be aware of the following concepts:
1. What are the Traffic Lights using D Flip Flop?
2. What is the role of D Flip Flop?
3. How does the circuit of D Flip Flop work in the Traffic Lights?
4. How can you simulate the circuit of Traffic Lights with D Flip Flop in Proteus?
In addition, you will find some important information about the Traffic Lights circuit in the DID YOU KNOW Sections. Let's start learning.

### Traffic Lights with D Flip Flop

Who is not aware of the traffic lights? we all observe and use the Traffic lights on the road every day. But for the sake of the concepts, let's see the traffic lights technically.
"The Traffic Lights are the signaling devices that has an electronic circuit designed to control the flow of traffic at the roads by a specialized pattern of lights."
These traffic lights are positioned at road intersections ad pedestrian crossing and other positions where the traffic flow has to maintain. The Traffic Lights depends on an array of three lights with different colors that are connected electrically The whole system is packed into a metallic structure. The LEDs turn on and off with a special pattern that depends upon the circuit. Before moving forward, refresh the concepts of Traffic Light with the logical point of view. There are three lights in the Traffic Light Signals. These are:
1. Red
2. Amber
3. Green
The red light stays last for some moments. The circuit is designed so, we get the output from the Amber color light that coordinates with the red and green light and lasts for some time. In the end, we get only Green light. All these lights are formed as a result of the sequential logic of D Flip Flop and at the end, the output of two D Flip Flops are inserted into AND Gate. The output of the Green light depends upon the AND Gate and we found the light of green LED only when the output of both the D Flip Flops are HIGH.

## Role of D Flip Flop in Traffic Lights

Have you ever thought about how does the traffic light blink at a specific time? We all follow the Traffic lights but today we'll learn that what does traffic light follows. The D Flip Flops are the logical circuits and we define the D Flip Flop as:
"The D Flip Flops a dual input is Flip Flop circuit that is designed to have the input at its D Terminal, regulates the signal with the clock edge pulses and shows the output at its two output terminals."
In the Traffic Lights, we use two D Flip Flops that are responsible for the switching of the lights in on or off conditions. The D Flip Flop is the combination of the S and R Flip Flops with an inverter with one terminal. but for  simplicity, we'll use the Integrated Circuit of D Flip Flop. Hence our circuit has only four components and we get a clean, easy and useful circuit that works automatically. The input Terminals are called CLK and D terminals whereas output terminals are denoted by Q and Q'.  The Truth Table for the D Flip Flop is given next:
 Inputs Output CLK D Q Q’ 0 X No Change 1 0 0 1 1 1 1 0
The X is called the don't care condition which means in this situation, the value of D does not matters. You can learn more about D Flip Flop in https://www.theengineeringprojects.com/2021/01/d-type-flip-flop-circuit-diagrams-in-proteus.html section. The output of the D Flip Flop is connected with each LED in the Traffic lights and hence we observe the on/off situations of Traffic Lights.

## Working of Traffic Lights circuit with D Flip Flop

The working of the Traffic Light starts with the change in the pulse of the clock.
1. The Q' output of the D Flip Flop 2 gives the power to the Red Light of the Traffic Light.
2. When the clock is low, there is no change in the Q' terminal of the 1st Flip Flop then the Amber light is off.
3. With the clock pulses, the Amber light of the Traffic Light turns on.
4. When the clock is high, we get the output inverse of the D Flip Flop.
5. The output Q of the D Flip Flop1 and the Q' of the D Flip Flop 2 is fed into AND Gate.
6. We know the AND Gate is HIGH only when both of its terminals are HIGH.
7.  This output of the AND Gate is connected with the Green Light of the Traffic Light.

## Circuit Simulation of Traffic Lights in Proteus ISIS

For the simulation of Traffic Light in Proteus, simply follow the easy steps coming next.

### Devices required for the Traffic Lights

1. D Flip Flop - DTFF
2. Traffic Lights
3. AND Gate
4. Clock pulses - DClock
5. Connecting wires
• Power up your Proteus software.
• Click the "P" button.
• Write the names of 1st three devices given above one by one and choose them.
• Get D Flip Flop twice, And Gate and Traffic Lights from the pick library and arrange them on the working area.
• Go to Generation mode(from the sidebar) >DClock and set it just on left side of the 1st D Flip Flop.
• Connect all the components with the help of connecting wires.
• Connect the Traffic Light's red light with the output of 1st D Flip Flop, the amber light with the D Flip Flop 2 and the green light with the output of AND Gate.
• Pop the play button.
Does your Traffic Lights are working well? great! if not, then check the connection again. if you face any problem then share with us. Consequently, today we learned about the logic behind the Traffic Lights. We learned that with the help of D Flip Flop, one can easily design a circuit just using four simple devices. We saw the working of the sequential on/off condition of the Traffic Lights. Stay with us for more interesting circuits.