Figure 1 is a circuit diagram of the transmitter. It consists of IC time base integrated circuits NE555, R1, R2, C1. The 1KHz low frequency oscillator modulates a high frequency oscillator consisting of a triode VT and peripheral components, and the modulated high frequency signal is transmitted from the C7 to the in-machine micro antenna to the space. C8 is used to widen the frequency band and prevent the influence of human body induction on the frequency. Actual use proves that this component is indispensable. 
figure 1
Figure 2 is a circuit diagram of the receiver. When the receiver receives the signal from the transmitter, the 2 pin of the integrated circuit TDA7000 outputs a low level, the music integrated circuit CW9300 has no high level trigger signal does not work, and the speaker BL is silent. When the item leaves more than 3m, the receiver does not receive the signal from the transmitter, the TDA7000's 2-pin output goes high, the CW9300 is triggered to work, and an alarm sounds from the BL to remind the item that it has been lost. 
figure 2
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The device consists of two parts: the transmitter and the receiver. The transmitter is placed in the baggage, and the receiver is carried around. When the item leaves itself more than 3m (meter), the receiver will sound an alarm to remind the attention and prevent the item from being lost. .
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