**Briefly Explain the Basic Working Principle of Traffic Lights**
Traffic lights are essential for managing vehicle and pedestrian movement at intersections, ensuring safety and smooth traffic flow. They operate using a sequence of red, yellow, and green lights to control the right of way. When the red light is on, vehicles must stop. The yellow light signals that the light is about to turn red, prompting drivers to prepare to stop. The green light allows vehicles to proceed. This cycle repeats in a controlled manner, often using automated systems to manage timing efficiently.
The system can be implemented using digital logic circuits, such as those based on the 74LS164 shift register, which helps in creating a sequential control mechanism. This circuit is used to generate the necessary timing and signal transitions, making it ideal for traffic light applications.
**1. Traffic Signal Control System Function Design**
At an intersection, the traffic signal control system manages the flow of vehicles from two directions: the main road and the branch road. Each direction has its own set of lights—green, yellow, and red. These are labeled as follows:
- **LMG**: Main Road Green Light
- **LMY**: Main Road Yellow Light
- **LMR**: Main Road Red Light
- **LBG**: Branch Road Green Light
- **LBY**: Branch Road Yellow Light
- **LBR**: Branch Road Red Light
The layout of these lights ensures that only one direction has the right to proceed at a time, preventing collisions and maintaining order.
**1.2 Normal Working Process of the Signal Lights (See Figure 2)**
In normal operation, the main road typically has longer green light durations due to higher traffic volume. For example, the main road might have a green light duration of 48 seconds, while the branch road may only have 24 seconds. When the green light turns off, the yellow light comes on for 4 seconds to warn drivers. During this time, the red light remains on for the other direction. A digital countdown display is also included to inform pedestrians and drivers of the remaining time, helping them make safe decisions.
**2. Traffic Signal Logic Circuit Design (See Figure 3)**
The logic circuit for the traffic signal system is designed using integrated circuits. It includes components such as a clock generator, a frequency divider, a main controller, and a decoding circuit. The clock source generates a standard 1Hz signal, which is then divided to produce the required timing intervals. The main controller, made up of a 74LS164 shift register, controls the sequence of the traffic lights by switching between different states.
**3. Circuit Analysis of the Traffic Signal Control System**
**3.1 Clock Source**
The clock source is built using a NE555 timer, which generates a stable 1Hz signal. This signal serves as the base for all timing functions within the system.
**3.2 Frequency Divider**
Two 74LS74 flip-flops are used to divide the 1Hz signal. The first divides it into a 4-second signal, and the second further divides it into an 8-second signal. These signals are used to control the timing of the traffic light states.
**3.3 Main Controller**
The main controller is a 14-stage ring counter constructed using the 74LS164 shift register. It cycles through four distinct states, each corresponding to a different combination of green, yellow, and red lights. The state transitions occur with each rising edge of the clock signal.
**3.4 Signal Lamp Decoding and Drive Circuit**
The decoding circuit uses logic gates to interpret the outputs of the main controller (Q5 and Q6) and drive the respective signal lights. The four possible combinations of Q5 and Q6 represent the four working states of the traffic lights. The circuit also includes a flashing mechanism for the yellow lights, which is achieved by combining the yellow light signal with a 1Hz pulse.
**3.5 Signal Operation Timing**
The timing of the traffic lights is carefully managed using the divided clock signals. For example, when the main road is green, the 8-second signal is used, while the 4-second signal is used during the yellow and red phases. This ensures that the lights change at the correct intervals.
**3.6 Digital Display Control Circuit**
A pair of 74LS190 counters is used to control the countdown displays. These counters start from a set value (e.g., 52 or 28 seconds) and decrement every second. The initial values are set using the yellow light signal, which triggers the counters to begin counting down.
**3.7 Digital Display Circuit**
The display circuit consists of 74LS245 and 74LS49 ICs connected to LED seven-segment displays. These displays show the remaining time for both the main and branch roads. The 74LS245 multiplexes the display signals, allowing the same set of digits to be used for both directions. This ensures that the countdown numbers are always synchronized.
The system is flexible and can be adjusted to accommodate different traffic conditions. For instance, the green light duration can be changed to 60 seconds for the main road and 30 seconds for the branch road, with the yellow light flashing for 5 seconds. This flexibility is achieved using a 5-divider circuit, such as the 74LS290, which adjusts the timing signals accordingly.
Fiberglass profiles, also known as FRP profiles, are widely used in fields such as construction, chemical engineering, power, transportation, etc. due to their lightweight, high strength, corrosion resistance, insulation, and other characteristics.
FRP Beam & FRP Bar,Frp Angle Bar,Fiberglass Angle Bar,Fiberglass Angle Profiles
Hebei Dingshengda Composite Material Co., Ltd. , https://www.frpdsd.com