Explore this engineering electronics science fair project that shows you how to design a system of signal lights using logic gates.
12th Grade – Age 17
Rajkot, Gujarat, India
Winner of the Virtual International Science Fair Contest
Create an automatic traffic signal system using a particular combination of logic gates.
From my 9th grade, physics and electronics have been my favorite subjects. The following research work has been done in accordance to the International Virtual Science Fair Contest, 2007 hosted by Super Science Fair Projects.
I have always wondered how the traffic signal on roads would be working. I have always questioned myself that how J.P. Knight might have introduced the first traffic signal on 10 December 1868, outside the British Houses of Parliament in London. This project gave me the chance to explore this invention, which would not have been possible in the regular school days. After a long struggle, my miniature design on automatic signal worked out, with a particular combination of logic gates.
Basic Theory Needed for the Engineering Electronics Science Fair Project:
As this is an open-ended project topic, there is no single definite procedure to design it. I have used my judgment and understanding to create this. I would like to explain the basic concepts I worked and thought upon for the success of my project.
➢ Logic gate: A digital logic system is concerned with just two voltage states. The signal processed by the system is either high or low, on or off, ‘logic 1’ or ‘logic 0’. At the heart of all digital systems are small switching circuits called logic gates. There are a number of different logic gates that open and give a high output signal, depending on the combination of signals present at their inputs. Logic gates are decision making circuits. Combinational logic is about combining logic gates to process two or more signals to produce at least one output according to a set of rules for each logic gates.
➢ Truth table: The set of rules which govern the behavior of logic gates are written in the form of a truth table. A truth table shows the value of the output for each of the possible input combinations.
➢ Not gate: Not gate or inventor has one input and one output. The transistor switch circuit, as I have shown in figure-1 acts as a NOT gate. Figure-2 shows the American symbol of NOT gate. The table below them depicts the truth table of the NOT gate. NOT gate produces a high output if the input is low and vice-versa. No matter what the input state is, the gate inverts it at the output. Figure-1 contains only transistor and resistor and is said to use Resistor-transistor-Logic (RTL).
➢ AND gate: It has two inputs A and B and one output F. This logic gate gives and output 1(high) only when both the inputs are 1(high). Figure-3 shows the circuit realization diagram. Figure-4 shows the symbol of AND gate and the table below it shows the truth table of AND gate.
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
• 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.
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.