Design of iPhone anti-theft circuit diagram

　　With the development of social economy and the improvement of people's living standards, mobile phones have become a necessity in people's lives due to their practicality and diverse functions. What follows is the trouble brought by mobile phone theft, which not only causes people's economic property losses, but also makes people's personal privacy unprotected. Therefore, mobile phone anti-theft has also become a matter of great concern to people.

　　Design and implementation of mobile phone anti-theft alarm. The circuit mainly includes three aspects: alarm signal generation, processing and output. Analysis shows that the circuit has a good alarm and anti-theft effect, suitable for various brands of mobile phone anti-theft design, and has strong practicality. In addition, the system has strong adjustability and is more convenient.

　　Circuit composition:  (1) Signal acquisition circuit. It is mainly composed of a pressure-sensitive sensor (piezoresistor) and three universal resistors to form a pressure-sensitive sensing bridge. The bridge is powered by the built-in battery of the mobile phone and consumes little power.

　　(2) Processing circuit. The processing circuit consists of three-stage amplification circuits.

　　(3) Output circuit. It consists of an output terminal and a parallel alarm.

　　Working principle: To realize the circuit's sensing of pressure. Its function is mainly realized by using the pressure-sensitive sensor to receive the pressure received by the mobile phone. When the pressure-sensitive sensor is stimulated by pressure, the balance of the bridge will be broken. A weak voltage Ui will be generated. The weak voltage is input into the processing circuit, that is, the three-stage amplification circuit. After Ui passes through the two operational amplifiers A1 and A2, the weak voltage is processed and transmitted to the in-phase input and inverting input of the operational amplifier A3. The potential difference between the in-phase and inverting input terminals of A3 can be adjusted through Rw, thereby changing the amplified voltage. The output can be adjusted through Rw. After the amplifier function of the operational amplifier A3, a large voltage is generated at the output end, which can power the alarm and make the alarm sound. The generated large voltage will also stimulate the human body. Thus, an anti-theft effect is produced.

　　Functions of each component: Pressure sensor and three R resistors: form a balanced bridge. Pressure sensor is used to receive external pressure; resistors have the functions of voltage division and current limiting. Inherited operational amplifier circuit: used to amplify weak signals