0 Preface
With the development of science and technology and the improvement of people's living standards, smart home has become a hot research field. The main problems facing the smart home problem are security theft, electrical control and other issues. The smart home can not only perform the alarm function for the owner when the problem occurs, but also provide the command operation of the owner of the smart home device, such as cooking or air cleaning through a terminal control device such as a mobile phone or a tablet computer.
Therefore, the sensors used in smart homes mainly include infrared sensors, magnetic sensors, and real-time clock chips.
1 How does the home monitoring system work?
The system is mainly composed of door magnetic alarm, infrared sensor alarm, gas sensor alarm, normal work, and user command execution.
1.1 Door magnetic alarm
The door magnetic system completes the safety monitoring of the door access and is mainly composed of a magnet and a reed switch. When the owner leaves the house, the anti-theft function can be activated. If the two are kept right, the two ends of the reed switch are in conduction under the action of the magnet. When the door is opened, the magnet and the reed switch are no longer in the opposite state. At this time, the reed switch is in the off state, and the system can alarm by SMS.
1.2 Infrared sensor alarm
When the user activates the infrared alarm function, in this state, if the infrared sensor detects an object contact, it can perform monitoring again after 10s, and then output an effective level signal (high level) through the sensor to alarm through the alarm. Then notify the user via SMS to complete the alarm function.
In order to increase the stability of the system, a microwave sensor or a magnetic sensor can be added to assist the infrared sensor to perform an alarm, which can better solve the false alarm problem.
1.3 Gas sensor alarm
The main component of the gas is CO. Therefore, the CO sensor is used for alarm detection. The CO sensor output signal line outputs an effective level signal for alarm. After the AVR microcontroller detects the CO sensor output voltage, it indicates that the gas content exceeds the standard at this time, and the control is executed immediately. The device performs an alarm. If the user is not at home, the user can be notified by sending a text message that the gas is exceeded. The user can control through the main control machine to eliminate the CO as soon as possible to ensure home safety.
1.4 Normal working condition
In the normal working state, each AVR MCU performs its normal work and collects data in real time. Once the data is found to be abnormal, after making a simple judgment, the data is exchanged to the host computer through the network, and the abnormality is reported and processed by the host computer. .
1.5 User Command Execution Action
When the user wants to operate the home device, the main control machine is notified by the short message, and the main control machine completes the identification of the short message, and notifies the respective electrical appliances to work through the communication device. At this point, the input of the controlled device and the output of the controller are electromagnetically isolated from the relay to complete the control of the entire home system.
2 hardware circuit design of home monitoring system
2.1 Power circuit design
A regulated power supply with a switching power supply. The power device of the switching power supply works in the state transition process, the power loss is small, the conversion efficiency is high, and the volume is small and the weight is light, and the size of the matching heat sink is also greatly reduced. The switching power supply has high efficiency and small volume. The output is stable and so on.
DC-DC conversion is realized by Boost boost converter. The IRF640 tube with small on-resistance and high switching speed is used as the switching tube, and the RHRP15120 is quickly restored to reduce the reverse conduction time and reduce the loss. The single-chip microcomputer and the pulse width modulation controller SG3525 jointly control the DC-DC conversion circuit through the double closed-loop circuit to achieve stable output voltage.
2.2 Infrared sensor circuit design
Infrared human detection plays a vital role in this system. It is very simple and easy to use the infrared detection chip BIS0001. Its typical circuit is shown in Figure 3.
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