# Traffic light sytem

Topics: Logic gate, Boolean logic, Integrated circuit Pages: 7 (1058 words) Published: December 5, 2013
CONTENTS:
1.Introduction.

2.System design.
A) Timing circuits.
B) Sequential circuits.
c) Combinational circuits.

3.Bill of materials.

4.Hardware design.

5.References.

6.Appendices.

1.Introduction:
This report is about the traffic light system through use of the digital logic design. The objective of this assignment is as follows: • To design and construct a prototype for digital logic circuit applications. • To apply and integrate the digital logic circuit principles taught in EEN1036. • To gain experience of hardware construction.

• To appreciate the importance of coordinated teamwork and project management. • To appreciate the nature of systems design.
The requirements of our assignment are listed below:
• resistors: 470 × 3, 22k, 100k • 555 timer IC, such as NE555 • capacitors: 0.1μF, 1μF 16V radial, 10μF 16V radial • 4017 counter IC • diodes: 1N4148 × 6

• LEDs: red, amber (or yellow), green • on/off switch
• 1M preset, horizontal • battery clip for 9V PP3
• stripboard: 20 rows × 21 holes
• Transistors: 2n3904
This project operates red, yellow and green in the correct sequence for the traffic lights.There are six lights to operate. The Red, yellow, and Green lights in the North-South direction will be designated as R1, Y1, G1. Similarly, the lights in the East-West direction will be called R2, Y2, and G2. 2. System design:

The system design of this project consists of the timing circuits, sequential circuits and combinational circuits which are all explained below. A)Timing circuits:
The time taken for the complete red - red & yellow - green – yellow sequence can be varied from about 7s to about 2½ minutes by adjusting the 1M preset. Some yellow LED’s emit light that is almost red so you may prefer to use a yellow LED. The 555 ICtimer stable circuit provides clock pulses for the 4017 counter which has ten outputs (Q0 to Q9). Each output becomes high in turn as the clock pulses are received. This is showed below:

B)Sequential Circuits:
We used a 4017 counter to control the traffic light sequence.The 4017 decade counter has ten outputs which go HIGH in sequence when a source of pulses is connected to the CLOCK input and when suitable logic levels are applied to the RESET and ENABLE inputs.The 4017 is designed to drive higher current loads, so it is OK to connect LEDs with series resistors directly to its outputs as show in our circuit diagram. We used the 4017 to control a sequence of events, for example, to generate a traffic light sequence. The traffic light sequence is shown below: Sequence StepInput BInput AOutput

00 0 1
1 0 0 1
2 0 0 1
3 0 0 1
4 0 1 0
5 1 0 0
6 1 0 0
7 1 0 0
8 1 0 0
9 1 1 0

This pattern shows the lights green or red for a suitably long time, with yellow and red+ yellow illuminated for shorter periods. The 1N914 diodes are used to make OR gates which control the LEDs. Outputs 0-3 illuminate the green LED, outputs 4 and 9 illuminate the amber LED and outputs 5-9 illuminate the red LED. Within the counter there are D-type flip flops which are joined together so that all the flip flops are clocked simultaneously.This results in logic states being passed along from one flip-flop to the next in sequence.Suppose the flip-flops have all been RESET, so that the A, B, C outputs are all logic 0. The D input to the first input will be at logic 1, as indicated in the first line of the table:

CLOCK PULSESD INPUTOUTPUT AOUTPUT BOUTPUT C
01000
11100
21110
30111
40011
50001
61000
Sequence repeats….

The rising edge of the first clock pulse transfers the '1' from D to A,...

References: We followed instructions using Digital Fundamentals by Floyd, and websites like www.doctronics.co.uk, www.educypedia.be/electronics/digitallogic.htm.
6. Appendices:
The data sheets for this project are on the next page.