Design of energy-saving control system for simulated street lamps

Today, when green electricity is advocated, street lamp energy-saving control has become a topic of increasing concern. Here, a set of simulated street lamp energy-saving control system is designed and produced. The structure of the energy-saving control system is shown in Figure 1.

Figure 1 Structure diagram of simulated street light energy-saving control system

Functions realized by the simulated street lamp energy-saving control system: The branch controller has a clock function, which can set and display the switch time, and control the entire branch to turn on and off the lights on time; it can automatically turn on and off the lights according to the changes in the brightness of the environment, and can automatically adjust the lighting status according to the traffic conditions; and can independently control the on and off time of a single street lamp; when the street lamp fails (the light is not on), the branch controller sends out an audible and visual alarm signal and displays the address number of the faulty street lamp. The unit controller has a dimming function, and the output power of the street lamp driver power supply can be automatically reduced according to the set requirements at the specified time. The power should be set and adjusted within the range of 20% to 100%, and the adjustment error should be ≤2%.

2 Overall design plan

2.1 Design ideas

The design uses PWM pulse width modulation technology and constant current source circuit to drive and adjust the brightness of street lamps . The working state of street lamps is controlled by single chip microcomputer, sensor and its detection circuit. The display part uses LCD display module, menu operation, display time, fault street lamp address, branch switch time, switch time of each lamp and other functions.

2.2 Design Principles

According to the structure diagram of the simulated street lamp energy-saving control system, the overall circuit is divided into five parts: environmental control circuit, clock circuit, traffic condition sensor detection circuit, display control module, LED constant current drive and fault detection circuit.

2.2.1 Environmental control circuit

The resistance of the photoresistor is inversely proportional to the light illuminance , and the voltage signal at both ends is sampled. The sampled voltage signal is used to control the switch of the LED lamp through the TTL level output by the Schmitt trigger. The circuit is reliable and effectively avoids malfunctions caused by drastic changes in light in a short period of time. The operator can easily debug it through the potentiometer.

2.2.2 Clock Circuit

Use the dedicated clock chip DS1302 for clock control, and a high-precision clock signal can be achieved by adding very little external circuitry.

The peripheral circuit is simple and reliable, with high time accuracy. The use of serial port communication can save I/O port resources, and time information can be stored by connecting an external lithium battery.

2.2.3 Traffic condition sensor detection circuit

Infrared sensors are used to determine whether an object has passed through a relevant position, and then sent to the microcontroller to determine and execute the relevant program. It has the advantages of photoelectric sensors and avoids the light interference of LED lights.

2.2.4 Display Control Module

Use 128 × 64 LCD dot matrix for information display, and use independent keyboard for function switching and time adjustment. Large amount of information, simple peripheral circuit, convenient operation through drop-down menu, and friendly human-machine interface .

2.2.5 LED constant current drive and fault detection circuit

The three-terminal adjustable voltage regulator integrated block LM317 is used to achieve constant current output. The PWM pulse width modulation method is used to control the brightness of the lamp. The brightness and power of the lamp can be accurately controlled, and the LED lamp transitions smoothly from dark to bright. The microcontroller can be selected to integrate two PWM pulse widths, which can easily generate the required PWM pulse width modulation signal.

2.3 System composition

2.3.1 Based on the above design ideas and design principles, the system composition block diagram is shown in Figure 2.

Figure 2 System composition block diagram

2.3.2 Logic diagram of each LED light control

The control logic diagram of each LED lamp is shown in Figure 3. The lamp is turned on when the specified time condition is met (light-on time) or the ambient light and dark conditions are met (dark to a certain degree); when an object (such as a person, a car, etc.) passes through the specified area, the lamp is turned on, and when the object leaves the specified area, the lamp is turned off, achieving energy saving requirements.

Figure 3 LED light control logic diagram

3 Unit Circuit Design

3.1 Ambient light control circuit

The environment control circuit detects the brightness of the ambient light and sends the detection signal to the single chip microcomputer P15, thereby realizing automatic turning on and off of the light. Figure 4 is a diagram of the environment control circuit.

Light and dark detection uses photoresistors RG1 and R12 (RP2) to divide the voltage, extract the voltage signal, and send it to the Schmitt trigger composed of a 555 timer. When the environment is dark to a certain degree (which can be easily adjusted through RP2), the resistance of RG1 rises, the Schmitt trigger flips, and the level signal is sent to the microcontroller for processing. C8 is designed for anti-interference. For example, when it is dark, there is interference from lightning. C8 prevents the voltage of pin 2 of 555 from changing suddenly to prevent malfunction. D2 is an indicator light for easy debugging.

Figure 4 Environmental control circuit diagram

3.2 Clock circuit

DS1302 is a high-precision clock integrated circuit that can count years, months, days, weeks, hours, minutes, and seconds. It is powerful.

The circuit is shown in Figure 5.

Figure 5 Clock circuit diagram

3.3 Traffic condition sensor detection circuit

The sensor detection circuit is shown in Figure 6.

The sensor uses E18-D80NK infrared sensor, which is a photoelectric sensor that integrates transmission and reception. When the target is detected, it is a low-level output, and in normal state it is a high-level output; the detection distance can be adjusted according to requirements.

Figure 6 Sensor detection circuit diagram

3.4 Display Control Module

The display control module is shown in Figure 7. See software design for control.

3.5 LED constant current drive and fault detection circuit

The constant current drive and fault detection circuit is shown in Figure 8.

Figure 8 is one of the LED constant current drive circuits. Constant current drive is the simplest two-terminal linear constant current drive circuit. It uses the three-terminal integrated voltage regulator LM317 to form a constant current circuit, and only two peripheral components are used :

Current sampling resistor R42 and anti-interference vibration elimination capacitor C9. J9, J10, and J12 are street lamp, voltage drop test terminal, and current test terminal respectively.

The constant current value I is determined by the value of R42: I = 1.25/R42.

1.25 V is the reference voltage of LM317. Conversely, according to the required constant current value I, the current sampling resistor can be calculated: R42 = 1.25 / I.

The maximum output current of LM317 can reach 1.5A, the working voltage difference is ≤40V, the current stabilization accuracy is high, which can reach ±1~2%, and it is equipped with over-current and over-heat protection inside, which is safe and reliable to use.

LM317 works in linear state, and its power loss P = UI. When the constant current value I is fixed, the power consumption can only be reduced by reducing the working voltage difference U. The appropriate working voltage difference is selected in the range of 4 to 8V.

If it is lower than 3V, the constant current will not be maintained.

The MCU outputs PWM and adds it to the gate of IRF540 to control its on and off to adjust the brightness (power) of the LED. The PWM frequency is generally 500 to 1000Hz. The PWM duty cycle is adjusted in the range of 20 to 100% through actual testing with a signal generator. When the frequency reaches about 1000Hz, the street lamp does not flicker.

Fault detection circuit, collects IRF540 drain voltage, obtains DC voltage signal through D6, R40, C7 peak detection circuit, compares with LM393 comparator 2 pin voltage, outputs level signal and sends to single chip microcomputer P10 for detection. According to the value of components in the figure, when the street lamp is normal, C7 voltage is 3.3V, 0V when the circuit is broken, and 7.2V when the short circuit is short. The actual circuit only detects the circuit break fault. Usually P1.0 is high level. When the circuit is broken, the voltage of 3932 pin is 0V, and the comparator flips and outputs low level. R39 adjusts the comparator reference voltage, which can be around 1V to prevent interference signal. R37 value is critical, affecting the discharge time of C7. After experiment, 300K is more suitable. The principle of short circuit detection is the same as above. Note that the PWM duty cycle can only be adjusted between 20% and 99.5%. When 100% PWM is output, IRF540 is always in the on state, C7 will not be charged, which will affect fault detection.

Figure 8 Constant current drive and fault detection circuit

Figure 9 Keyboard and LCD display flow chart

4 Software Design

The key to software design is to set up the street light control and LCD operation interface as required.

4.1 Functions implemented by the software

(1) Clock function. (2) Street light control. (3) 2-way PWM control. (4) Keyboard and LCD display.

4.2 Keyboard and LCD display

The LCD display and function settings adopt menu-based operation, and the flow chart is shown in Figure 9. The LCD has a Chinese character library, and the operation interface is friendly and convenient. Four multi-function keys and a return key are set to complete the entire street light control setting and PWM output.

4.3 Street light control flow chart

5 System Testing

5.1 Clock Setting Test

Through the menu operation, enter the time setting, and the light switch setting.

Set the current time to the time for switching lights on and off: During the actual measurement, the current time was set to 20:00, the switching on time of both lights was set to 18:00, and the switching off time was set to 6:00. The moving objects were tested according to the design requirements and met the requirements.

5.2 Test of ambient light and dark changes

At night, cover the photoresistor with an object, adjust PR2 to turn off the light, and the indicator D2 goes out, indicating that the adjustment is completed. Turn off the light and move the object to test according to the design requirements, and the requirements are met.

5.3 Independent time control settings

Set the on/off time of the two lights separately. One meets the on-time condition, and the other does not meet the time condition.

The moving object is tested according to the basic requirements. The street lights that meet the lighting time conditions will turn on and off as required, and the street lights that do not meet the time conditions will be off for a long time. The results of swapping the lighting conditions of the two street lights are consistent.

5.4 Remove street light 1 (simulate circuit breakage), meet the time conditions, and move the object according to the basic requirements. Street light 1 should light up, the buzzer sounds, the warning light flashes, and the LCD displays L1 failure. Street light 2 also meets the requirements. The actual LED light failure is basically a circuit breakage, so only a circuit breakage test is performed.

5.5 Since the on and off of the street light LED is controlled by PWM, as long as the PWM signal can be adjusted within 20% to 100% and the error is less than 2%, the output power of the street light power supply can meet the design requirements. In actual tests, the PWM signal can only be adjusted between 20% and 99% (see 2.5), with a maximum error of 1%, which meets the design requirements.

6 Conclusion

The simulated street lamp energy-saving control system has been tested and fully meets the design requirements and work needs. The control system operation interface is simple and easy to understand, and the single power supply makes the circuit concise and clear with low cost. The ambient light control circuit, constant current drive and fault detection circuit have outstanding design features, and the traffic condition sensor detection circuit is economical and practical. The entire simulated street lamp energy-saving control system has broad application prospects and has development and application value.