FPGA Design of Traffic Light Control Circuit

1 Introduction

With the continuous increase in the number of motor vehicles in society, especially in cities, the traffic control of vehicles is becoming more and more important in the daily operation control of modern cities. At crossroads, more and more traffic lights are used for traffic command and management. This paper uses VHDL hardware description language as a design method to complete the development of traffic light control circuit. The purpose of the development of traffic light control circuit is to design a control system for red, yellow and green traffic lights suitable for crossroads of main and branch roads. By reasonably designing the system function, the conversion of red, yellow and green lights has an accurate time interval and conversion sequence. Of course, this requires an automatic and safe system to control the conversion of red, yellow and green lights. The designed traffic light control circuit is simulated in QuartusII 5.0 software, its waveform is observed, and the program is downloaded to the target FPGA device for hardware debugging and verification, which proves that the designed traffic light control circuit can fully realize the predetermined function and has certain practicality.

2 System Design Requirements

The traffic light control circuit to be designed should be applicable to the crossroad formed by the junction of a main road and a branch road, and the flashing time of the traffic lights on the main and branch roads is not exactly the same. The specific design requirements are as follows: to control the crossroad formed by the junction of a main road and a secondary road, so that vehicles and pedestrians on the main and branch roads can pass alternately, where vehicles and pedestrians on the main road pass for 60 seconds, and vehicles and pedestrians on the branch road are prohibited from passing; vehicles on the branch road pass for 30 seconds, and vehicles on the main road are also prohibited from passing. Whenever the signal light changes from green to red, the yellow light must be on for 5 seconds, and the red light on the other main road remains unchanged and is prohibited from passing. Before the yellow light turns on, the green light flashes at a frequency of 1HZ for 5 seconds to prompt vehicles and pedestrians. Digital tubes are installed on the main road to display the flashing time of each signal light on this road.

3 System design and logic design

3.1 System Design

By referring to other relevant literature ^{[1], [2], [4], [5], [6], [7]} , and comparing the advantages and disadvantages of other design methods such as those based on single-chip microcomputers and discrete components, we believe that the design method based on FPGA has obvious advantages such as short cycle, flexible design, and easy modification. In addition, with the development and improvement of FPGA devices, design languages, and electronic design automation tools, more and more electronic systems are designed using FPGAs. In addition, once the electronic system designed by FPGA can reach a certain scale of mass production, it is easy to convert it into ASIC chip design. It is believed that in the future, FPGA design methods will be applied to various types of electronic system designs on a larger scale. Therefore, we decided to use VHDL hardware description language to program and implement the system design requirements, and adopted a top-down design approach to divide the system into 6 modules, namely traffic light control module, display control module, display decoding module, 60-second timer module, 30-second timer module, and 5-second timer module. As shown in Figure 1.

Figure 1 Module division of traffic light control circuit

3.2 Logic Design

According to the system design scheme determined above, using modular design ideas, we designed the VHDL programs of the traffic light control module, display control module, display decoding module, 60-second timer module, 30-second timer module and 5-second timer module in the QuartusII 5.0 software system, and successfully designed the traffic light control circuit through reasonable connection and coordination of the ports between the programs of each module, and obtained its logical structure schematic diagram, which is the logical structure of the entire traffic light control circuit.

4 Design Verification

Through simulation in QuartusII 5.0 software, it is verified that the circuit can realize the predetermined function, that is, the main and branch roads are open alternately, the main road is open for 60 seconds, and the branch road is open for 30 seconds. Before the green light turns to red, the yellow light is on for 5 seconds, and the red light of the other main road remains unchanged. After the yellow light is on for 5 seconds, the green light of the other main road is on, and the red and yellow lights are not on. At this time, the main road is allowed to pass, and the main road has a digital display of the time when each light is on. This cycle is repeated to realize the traffic control of the crossroad. In addition, we have also realized an additional function, that is, when there is no car passing through the branch road, the main road is always in a smooth state, so that when encountering special situations in practice, it can be flexibly controlled and applied. In addition, a manual control terminal can be added, that is, when there is a need for traffic control, the traffic police can manually control the conversion of the intersection signal lights.

In order to simulate and verify the function of the circuit more accurately, we classified it according to various traffic conditions in real life, set multiple scenarios that appear at the intersection, and performed functional simulation on the designed system circuit for each set scenario in the QuartusII 5.0 software environment. Figures 2 to 5 are the experimental simulation results of several set scenarios (the input variables SM and SB in the figure are the main and branch road sensor signals, CLK is the clock signal from the clock generation circuit, the output signals MR, MY, MG are the red light, yellow light and green light on the main road, BR, BY, BG are the red light, yellow light and green light on the branch road, and OUT1 and OUT2 are the main road outputs, and OUT3 and OUT4 are the branch road outputs). By observing the experimental simulation results under these scenarios, we found that the functions that meet our expectations can control the sequential conversion of traffic lights at intersections in an orderly and accurate manner, and no misoperation occurs.

In addition to software simulation, we also downloaded the entire program to the target FPGA device, used the corresponding hardware circuit to perform hardware debugging, and verified that the circuit worked well and was completely consistent with the results of the software simulation. This shows that the traffic light control circuit we designed has passed the software simulation and hardware testing and can complete the previously planned functions.

Figure 2 Simulation results of traffic light control circuit 1

Figure 3 Traffic light control circuit simulation results 2

Figure 4 Simulation results of traffic light control circuit 3

Figure 5 Simulation results of traffic light control circuit 4

5 Conclusion

The experimental simulation results show that the traffic light control circuit we designed can complete the corresponding control well and realize the predetermined functions. Through hardware download and debugging, the circuit works normally and the control results fully meet the corresponding requirements.

The author's innovative idea is to use VHDL language to design a practical traffic light control circuit. Through software simulation and hardware debugging, the circuit completes the predetermined function. If the circuit function is further improved and perfected, it can fully achieve practical purposes after being commercialized.

References

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