Design of Network Node and Power Circuit of Wireless Alarm System for Smart Appliances

MOS power IC full range

KKST patch plug-in active passive crystal oscillator hot sale 24.576000MHZ

A wireless alarm system for home appliances based on wireless network technology is designed. The wireless alarm system provides real-time monitoring of the entire home security environment. The scope of monitoring includes a series of unsafe factors such as indoor theft, fire alarm, gas leak, and water pipe rupture. Once the above-mentioned safety accident occurs, the alarm system will issue corresponding alarm information, which can enable the head of the household to take effective emergency measures immediately after receiving the alarm information to urgently handle the accident.

Wireless alarm network node hardware design

The wireless alarm network node is mainly composed of a microprocessor AT89C2051, an nRF2401 wireless communication chip, a peripheral device and a sensor of a digital input interface. The microprocessor AT89C2051 is the core control component of the hardware system of the entire network node. It is responsible for receiving the switch alarm signal triggered by the sensor, transmitting the nRF2401 communication command, and transmitting the control information. The single-chip RF transceiver chip nRF2401 is a key device for wireless data transmission. The nRF2401 operates in the 2.4-2.5 GHz ISM band. The chip has built-in frequency synthesizer, power amplifier, crystal oscillator and modulator. The output power and communication channel can be configured through the program. The power consumption of the chip is very low, and the power is transmitted at -5dBm. When the working current is only 10.5mA, the working current is only 18mA when receiving, a variety of low-power working modes, energy-saving design is more convenient. The network node uses nRF2401 for data transmission to realize wireless transmission of alarm information. The network node senses abnormal changes in the external environment through the connected sensors. The circuit schematic of the network node is shown in Figure 2.

In the network node, the power source is the energy center, which plays a very important role in the node. Especially in the wireless communication system, the power source is not only the energy supplier, but also directly affects the quality of the communication. The device is usually limited to the voltage applied to the input pin or output. These pins are connected to Vcc by diodes or separate components. If the voltage applied is too high, current will flow to the power supply through the diode or separate components. The current voltage output module is mostly 5V, so it is necessary to design a 5V to 3V voltage regulation module with stable output. In this system, the LM1117 is designed to provide a conversion voltage for the communication control chip, which has the advantages of low power consumption and small size. And because the voltage contains many sources of high frequency interference, these high frequency components can easily enter the communication system through the power supply. In addition, the transmission frequency of the system itself will also be interfered by the power supply feedback to the communication system. Fiercely, a 220μH inductor can be added to the power supply circuit, and a filter circuit composed of a plurality of capacitors having different capacitance values ​​can be used to suppress various high-frequency signals. Enables the node to obtain a stable, reliable and low-interference power supply to ensure reliable operation of the node. The power supply circuit is shown in Figure 3.

The main problems encountered in the design process of the network node and the solutions are: nRF2401 RF circuit works in the 2.4GHz ~ 2.5GHz high frequency working frequency band, the anti-interference design is directly related to the RF performance and the operation of the entire network node. When wiring in the wireless communication part, reasonable layout and wiring and the use of multi-layer boards are both necessary for wiring and an effective means to reduce electromagnetic interference and improve anti-interference ability.

According to the characteristics of wireless network technology, the composition scheme of intelligent home appliance alarm system based on wireless network technology is proposed. The system has no modularity and has a good portability and scalability. A small alarm system was set up in the laboratory for experiments. The preliminary experimental results show that the alarm system based on wireless network technology has higher communication efficiency and better stability.