Child missing reminder

When you take your children out for a trip, you may be most worried about the child getting lost. This device can effectively solve this problem. The device consists of a transmitter and a receiver. Put the transmitter in the child's pocket and the receiver is held by the adult. When the child is more than 3m away from the adult, the receiver will sound an alarm to remind the adult to pay attention and prevent the child from getting lost.

Figure 217-1
Figure 217-1 is the transmitter circuit diagram. It consists of IC time base integrated circuit NE555, R1, R2, C1. The 1KHz low-frequency oscillator modulates the high-frequency oscillator composed of triode VT and peripheral components. The modulated high-frequency signal is transmitted from C7 to the internal micro-antenna to space. C8 is used to widen the frequency band and prevent the influence of human induction on the frequency. Actual use proves that this component is indispensable. Figure 217-2 is the receiver circuit diagram. 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 does not work without a high-level trigger signal, and the speaker BL is silent. When the child is more than 3m away from the adult, the receiver cannot receive the signal from the transmitter, the ② pin of TDA7000 outputs a high level, CW9300 is triggered to work, and an alarm sound is issued from BL to remind the adult that the child has gone far away.

When making Figure 217-2
, the inductor L in the transmitter is wound 3 turns of Φ1mm enameled wire on a Φ7.5mm pencil and then removed. The inductor L in the receiver is wound 5 turns of Φ0.51mm enameled wire on a Φ5mm drill and then removed.