Research and design of smart home lighting system

With the development of science and technology, more and more automated and intelligent products are entering people's lives. Smart homes are gradually replacing traditional homes and becoming an industry development trend. As an important subsystem of the smart home system, the smart home lighting system has the advantages of high efficiency and energy saving, simple management, diverse control, low cost and easy entry into the market. This paper studies and develops the smart lighting system for smart homes, and completes a low-cost smart home lighting system controlled by a single-chip microcomputer.

1. Overview

The smart home lighting system belongs to a subsystem in the smart home and can also be used alone. The smart home lighting system can control various lighting effects in different living areas and occasions to easily solve the problem of home energy saving and improve the quality of life. In life, such a problem is often encountered. When watching TV or reading in the living room, you don’t need too strong lighting light, so you have to turn off the living room headlights and turn on other lamps with relatively dim light to meet the needs of watching TV or reading. In order to meet the lighting requirements of different occasions, it is necessary to install a variety of lamps, which brings great inconvenience to the control of lamps. The smart lighting system can easily solve this problem. Just press the remote control in your hand to change the scene lighting.

The solution for the control method of the smart home lighting system is divided into wired and wireless methods. Wired methods include X-10 and CEBUS of power line carrier, HomePNA of telephone line, IEEE802.3 of Ethernet, LONWORKS and IEEE1394 of dedicated bus, etc. The advantage of using power line as the transmission medium of network information is that it does not need to lay cables separately, which reduces the difficulty of construction; the disadvantage is that the transmission rate is only 300Kbps, which is difficult to meet the transmission of video and audio signals, the confidentiality is poor, and the access equipment is expensive. Wireless methods include IrDA of infrared method, IEEE802.11 series of wireless LAN method, HomeRF of home radio frequency technology, IEEE802.15.1 of Bluetooth, IEEE802.15.4 of ZigBee, etc.

The wireless method solves the wiring problem and can also meet the transmission of video and audio signals. This article introduces a smart home lighting system based on 2.4G radio frequency technology.

2. System solution

The system solution block diagram is shown in Figure 1. This solution uses STC12C5A08AD as the MCU controller. STC12C5A08AD is the latest generation of single-chip microcomputer of Hongjing Technology Company. It adopts the 6th generation confidentiality technology. The program cannot be decrypted after burning, which enhances the confidentiality function. The speed is 8~12 times faster than the ordinary 8051 single-chip microcomputer, with 4 built-in 16-bit timers and relatively low power consumption. The control signal of MCU controls the brightness of the lamp through the optocoupler to control the thyristor. A current detection loop is added to the strong current control interface to detect the size of the strong current for detection feedback. The communication method uses a 2.4G wireless communication module, which does not require wiring, reduces costs, has flexible control methods, a wide remote control range, and fast communication speed. This solution can control a total of 12 lamps and is suitable for home lighting control.

Figure 1 System solution block diagram

3. 2.4G module

Common general-purpose chips used for 2.4GHz communication include the nRF2401 wireless chip module of Nordic Company of Norway and the RFW102 wireless chip module of RFWave Company of Israel [5]. Based on design requirements and cost considerations, this design uses the nRF2401 of Nordic Company for wireless data transmission.

The nRF2401 is a single-chip wireless transceiver chip that operates in the 2.4GHz ISM band and fully integrates power synthesizer, power amplifier, crystal oscillator and adjustment circuit. It uses QFN24 5×5 mm package and the application circuit uses few peripheral components (see Figure 2); it uses FSK modulation and 125 channels to meet the needs of multi-frequency and frequency hopping; the transmission rate is as high as 1Mbps, with high data throughput; low power consumption, the power supply voltage of 1.9V~3.6V meets the needs of low power design; the chip is equipped with a special voltage regulator circuit, and it has good communication effect when using various power supplies including DC/DC switching power supplies.

Figure 2 2.4G communication circuit

4. Lighting control

Common dimming methods include: pulse width modulation (PWM) dimming, dimming by changing the supply voltage of the half-bridge inverter, pulse frequency modulation dimming, pulse phase modulation dimming and thyristor phase-controlled dimming. The thyristor phase-controlled dimming method has the advantages of small size, reasonable price and wide dimming power range. This system finally uses thyristor phase-controlled dimming to adjust the brightness of the lamp.

Applying the thyristor phase-controlled principle, by controlling the conduction angle of the thyristor, a part of the sine wave voltage input from the power grid is cut off to reduce the average value of the output voltage, so as to control the supply voltage of the lamp and realize dimming. Thyristor phase-controlled dimming has a fast voltage regulation speed for the lighting system, high dimming accuracy, and the dimming parameters can be adjusted in real time in different time periods. Since the dimming circuit is mainly composed of electronic components, it is relatively small in size, light in weight and low in cost.

The thyristor phase-controlled dimming circuit is shown in Figure 3. The control signal of the microcontroller is inverted by 74HC04 and sent to the optocoupler MOC3023. After photoelectric isolation, it is input to the control electrode of the thyristor T16C6F to control the conduction angle of the thyristor and realize dimming.

Figure 3 Thyristor phase-controlled dimming circuit

5. Conclusion

The smart home lighting system based on single-chip microcomputer control has the advantages of low cost, short development time, convenient installation and maintenance, and easy to meet the different needs of customers, and has broad market prospects. At present, China's consumption level is not high, and there is not much demand for high-end smart homes with large systems. However, the low cost of smart home lighting systems is increasingly widely used in the home market. The smart home lighting system based on single-chip microcomputer control introduced in this article has certain market promotion value.