Traffic Light Control System Design with Moore Machine Logic

This report details the design and implementation of a two-way traffic light control system using a Moore finite state machine in Logisim. The system features traffic lights for the north-south and east-west directions, each with red, green, and yellow signals. The signals are controlled by a synchronous digital clock and a 'Safe' signal, which adjusts the timing of the green lights based on pedestrian safety. The report includes state representations, Boolean logic functions derived from K-map reduction, circuit diagrams, and testing results, demonstrating the correct operation of the traffic light signals according to the defined truth table. The use of K-map techniques simplifies the Boolean logic functions to make the final circuit.

Running head: TRAFFIC LIGHT CONTROL SYSTEM
TRAFFIC LIGHT CONTROL SYSTEM
Name of the Student
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Author Note

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Introduction:
In this particular report the design of a two way traffic light system is constructed in Logisim
by using a Moore finite state system as discussed in the later section. One traffic light is
placed in the north-south direction and another traffic light is placed in the east-west
direction. Each of traffic light has three signals namely Red, Green and Yellow signal. Red
signal indicates to stop traffic in the corresponding direction, green means traffic can go in
that direction and yellow signal is to wait for signal to become either Green or Red. The
signals in North-South is given by the names R1, G1 and Y1 according to their colours and
similarly the signals in the East-West direction is given by the names R2, G2 and Y2. The
traffic lights will change its signals i.e. exactly one light of the three signals in a traffic light
will glow if the logic input to it is 1. The change of signals will occur with the high input of a
synchronous digital clock which is supplied to the Moore machine. There is another digital
input signal called Safe signal which indicates crossing the street is safe when the signal is 1
and crossing street is dangerous when it is 0. When the safe signal is 0 the green signal in
each traffic light will occur in a delay. Hence, the input to the system is one and outputs of
the system is total of six (three north-south signals and three east-west signals).
State representation and Boolean Logic function:
In this Moore machine there are a total of six states and the machine is designed using three
flip flops. The state transition occurs depending on the combination of the flip flops. The flip-
flops are Q1, Q2 and Q3 respectively. There are total 8 combinations of the states and of
them states of two 2 combinations are don’t cares. The state table along with the outputs are
shown below.
State Q1 Q2 Q3 R1 Y1 G1 R2 Y2 G2
1 1 0 0 1 0 0 0 0 1

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2 1 0 1 1 0 0 0 1 0
3 1 1 1 1 0 0 1 0 0
4 0 1 1 0 0 1 1 0 0
5 0 1 0 0 1 0 1 0 0
6 1 1 0 1 0 0 1 0 0
7 0 0 0 X X X X X X
8 0 0 1 X X X X X X
Now, when the Safe signal is taken as input which has two states 1 or 0 then the total states of
the machine will be 16. Now, for simplification the combinations of R1, G1, Y1, R2, G2 and
Y2 are represented by three states namely D1, D2 and D3. The truth table with the added
input Safe is shown below.
Safe Q1 Q2 Q3 D1 D2 D3
0 0 0 0 X X X
0 0 0 1 X X X
0 0 1 1 0 1 0
0 0 1 0 1 1 0
0 1 0 0 1 0 1
0 1 0 1 1 1 1
0 1 1 1 0 1 1
0 1 1 0 1 0 0
1 1 0 0 1 0 1
1 1 0 1 0 1 1
1 1 1 1 X X X
1 1 1 0 X X X

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1 0 0 0 X X X
1 0 0 1 X X X
1 0 1 1 0 1 0
1 0 1 0 1 0 0
Hence, by using K-map reduction the simplified Boolean equations are
D1 = S’*Q2’ + Q3’
D2 = S’*Q1’+ Q3
D3 = Q2’ + Q1*Q3
Circuit Diagram:
Testing:

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Hence, from the testing it can be seen that the outputs of North-south and East-west signals
are working according to the above truth table based on Q1, Q2, Q3 and Safe signal. Thus the
Circuit implementation of the Synchronous clock triggered Moore state machine for traffic

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light control is appropriate and the circuit is very simple as the K-map techniques of reduced
Boolean logic function is used to make the final circuit.