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Winner of the International Virtual Science Fair Contest held by Super Science Fair Projects.
Physics  Electronics Signal Lights
See the beginning of this project on physics and electronics science fair projects.
Applications of Concepts to Create an Automatic Traffic Light Signal:
A traffic light, also known as a traffic signal, stop light, stop-and-go light, robot, or semaphore, is a signaling device positioned at a road intersection, pedestrian crossing, or other location in order to indicate when it is safe to drive, ride, or walk using a universal color code. It is a very complicated device and thus I was able to create a miniature form of it. As we know, a traffic signal looks something similar to the given figure:
I used a particular combination of AND gate & NOT gate to create a design of traffic signal. Figure-6 below shows the design of my automatic traffic signal system.
The problem required a system which lights 3 lamps- Red(R), Yellow(Y) and Green (G) in the correct sequence to drive a traffic light. After I inspected all the possibilities and went into the depth of the problem, I concluded that the way a traffic light works showed that there is a four state cycle which can be built from two input logic gates. Thus, I created a design which I have showed above and created it. After many small minute errors, I could create a perfect automatic traffic signal system. The following table illustrates the truth table which is a combination of NOT & AND logic gates which made up the traffic signal.
Truth table which is a combination of NOT & AND logic gates which made up the traffic signal:
INPUT | OUTPUT
| A |
B |
Y |
R |
G |
| 0 |
0 |
1 |
0 |
0 |
| 0 |
1 |
1 |
1 |
0 |
| 1 |
0 |
0 |
0 |
1 |
| 1 |
1 |
0 |
1 |
0 |
Observations:
• Red has to be lit when A is 0 and B is 0 or A is 0 and B is 1.
• Yellow has to be lit when A is 0 and B is 1 or A is 1 and B is 1.
• Green is lit when A is 1 and B is 0.
Conclusions:
The logic circuit of an automatic traffic light signal can be built by feeding R from A via an inverter, Y from B directly and G from the output of an AND with A and B inverted as the inputs.
There are several uses of this design of automatic traffic signal. I have given some of the various uses:
1. The students of secondary school can be briefed about this to develop their interest in electronics.
2. The design gives one an exposure to the very usual things around him/her.
3. It can be used as a basic design for people to make simple traffic lights.
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