introduction The current remote control system of household appliances generally realizes remote control through the Internet or the public switched telephone network. However, with the increasing popularity of mobile phones, it is possible to use GSM short messages to achieve remote monitoring of home environments and home appliances. Compared with the remote control mode of the telephone, it is free from the restraint of the telephone line on the equipment; compared with the remote control of the computer, the equipment and the use cost are reduced. There have been many studies on the use of GSM networks to monitor home security, greenhouses, street lights, vending machines, etc. Most of these studies are realized by using GSM networks to remotely control relays. The GSM-based home appliances and home environment monitoring system designed in this article is mainly aimed at many current home appliances with infrared remote controls (such as water heaters, air conditioners, TVs, set-top boxes, etc.), through the GSM network and the replication of home appliance remote controls To control household appliances. 1 Working principle of the system A GSM-based home appliance and home environment monitoring system consists of a GSM short message module that can send and receive text messages as an upper computer, an intelligent controller (single chip microcomputer), a temperature sensor, and a home appliance with an infrared remote controller (such as a water heater and air conditioner) as a lower computer , TV, set-top box, etc.). First of all, the system is initialized. The single-chip microcomputer reads the upper temperature limit set by the user and the target number for sending the alarm message from the keyboard, and displays it through the LCD display. When the MCU detects that the user presses the infrared learning key, it enters the infrared learning interrupt service program, reads the infrared signal emitted by the remote control of the external appliance, decodes the infrared signal, redefines the code length, groups, and saves, thereby learning the remote control器 [728]. After the initialization is completed, the MCU cyclically reads the value of the temperature sensor DS1820 and compares the upper temperature limit set by the user with it. Once the current temperature is found to exceed the upper temperature limit, the GSM module TC35i is controlled to send an alarm to the user's mobile phone through the GSM network SMS. At the same time, the MCU cyclically inquires whether the serial port has received information. If received, it reads the information into the MCU, parses out the content of the short message is what kind of instruction the MCU is required to send to the household appliance, and passes the infrared signal representing the instruction through the infrared emission tube Launched to control household appliances. The system block diagram is shown in Figure 1. Figure 1 System block diagram 2 System hardware design The home appliance and home environment monitoring system based on GSM mainly uses AT 89S52 single-chip microcomputer as the intelligent control center, 4 @ 4 keyboard and 1602LCD display as human-computer interaction equipment, GSM communication module selects TC35i, DS1820 temperature sensor for temperature acquisition; through HS0038B infrared The receiving head receives the infrared signal to complete the demodulation and amplification of the infrared signal; at the same time, the square wave generator function of the P1.0 port of the AT89S52 microcontroller is used to form the infrared signal modulation device, and the infrared LED is used as the infrared emission device. 2. 1 GSM module and single chip connection The GSM module TC35i is a 3.3 V CMOS component, which requires the starting current of the power supply to exceed 2 A, and the starting voltage to reach 4.2 V. Therefore, the power supply chip LM2596.TC35i, which can provide a maximum of 3 A current, is used. Connect to the power output pin of LM2596. Pins 6 ~ 10 are grounded and pins 25 ~ 27 are connected to the SIM card. In order to display the working status of TC35i, connect an LED indicator to the ground at pin 32. After the TC35i is started, you can send data and commands to the TC35i through the serial port through the microcontroller. The baud rate of the TC35i is adaptive. Here, the baud rate of 9600 is used. As long as the RXD and TXD of the TC35i are connected to the TXD and RXD of the microcontroller, respectively That's it. The circuit diagram is shown in Figure 2. Figure 2 Connection of TC35i and MCU 2. 2 The connection of infrared receiver and single chip The infrared receiving head HS0038B is an infrared receiving chip that integrates functions such as demodulation, filtering, and amplification. It demodulates the infrared signal modulated on the 38 kHz square wave and outputs the square wave through the OUT pin. HS0038B usually outputs high level, when there is remote control signal input, its output is high and low level pulse, so a code consists of a low level followed by a high level when receiving. Different combinations of high, low and low levels can be used to form different codes. In this system, the infrared signal will be read in an interrupt mode, so the OUT pin of HS0038B is connected to the external interrupt 0 of the microcontroller. The connection between HS0038B and single chip is shown in Figure 3. Figure 3 The connection of infrared receiver H S0038B and single chip microcomputer
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