An electronic anti-lost alarm design scheme for color LCD touch screen
0 Preface
In the modern society where work and life are fast-paced, old people, children or pets are lost; valuables such as mobile phones and luggage are stolen; and things such as keys and wallets are forgotten almost every day. The electronic anti-lost alarm is a security product that can reduce the loss and inconvenience caused by forgotten or lost items. Based on the application status and development needs of electronic anti-lost alarm, this paper uses RFID technology to design an electronic anti-lost alarm with color LCD touch screen, which provides a better application for the application of Internet of Things technology and security products. Application plan.
With the functions of DPL and ACK PAYLOAD of nRF24L0l chip, combined with the touch screen design method, this paper designs an electronic anti-lost alarm based on nRF24L01, ATmega48PA and TFT graphic LCD, which can effectively protect the guarded elderly, children or protected items. The role of ground defense, anti-theft, anti-forgetting. The high-performance controller is used to realize the independent control of color LCD touch screen display, wireless remote control and MCU system. The system has high humanized service level and strong practicability, and has good technology promotion and market application prospects.
1 system design
The system structure is shown in Figure 1. The electronic anti-lost alarm is composed of a host and a slave, and the host is placed at the master, and the slave is placed on the protected object such as an elderly person, a child or a mobile phone. The electronic anti-lost alarm is embedded in the microprocessor in both the host and the slave. When the device is working normally, the slave sends a stable radio wave, and the host does not alarm after receiving the radio wave. When the distance between the host and the slave exceeds the predetermined distance, the host does not receive the radio signal of the handset, and immediately whistle alarm (sound pressure ≤75 dB) with vibration to attract the user's attention. If the search mode is started by pressing the search button of the host, the wearer of the host can find the protected object through the prompt information of the liquid crystal touch screen and the gradual or fade-in change of the alarm sound. Under normal circumstances, the lithium battery is connected to the power adapter or the computer with a USB interface.
2 hardware design
2.1 AVR microprocessor control circuit
ATMEL's ATmega48PA is used as the main control unit of the microprocessor. The chip is a high-performance, low-power 8-bit microprocessor with an operating voltage of only 1.8 to 5.5 V and an operating frequency of 0 to 20 MHz. KB system programmable FLASH. As shown in Figure 2, ATmega48PA peripheral circuit includes power circuit, 8M clock circuit, reset circuit and USB / ISP download interface.
The power supply circuit is shown in area 1 of Figure 2. A nominal 3.7 V lithium battery is connected to the input of the integrated three-terminal regulator chip REG1117-3.3 V. REG1117-3.3 V stabilizes the output of 3.3 V DC voltage and supplies it to the system power module.
The clock circuit is shown in area 2 of Figure 2. The ATmega48PA has an internal RC oscillator circuit that produces an oscillation frequency of 1 MHz, 2 MHz, 4 MHz, and 8 MHz. When the system requires a more accurate baud rate, it needs to be implemented by an external circuit.
The reset circuit is shown in area 3 of Figure 2. The ATmega48PA has a built-in power-on reset, and the fuse bit can control the reset time. Therefore, when the external reset circuit is powered up, you can directly pull a 10 kΩ resistor R3 to VCC. A 10 μF capacitor C11 is used to eliminate interference and clutter.
The ISP download interface is shown in area 4 of Figure 2, using a dual-row 2 & TImes; 5 socket access interface. Since there are no peripheral components, PB3 (MOSI), PB4 (MISO), PB5 (SCK), and RESET pins are not interfered with by the ISP download interface and can still be used normally.
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