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Children anti-lost reminder circuit

2014-11-08 08:57  
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Children anti-lost reminder circuit
Children anti-lost reminder circuit
Figure 1 shows the transmitter circuit. It consists of time-base IC NE555, R1, R2, C1. 1KHz low-frequency oscillator can modulate the high-frequency oscillator composed of transistor VT and peripheral components, then the modulated high-frequency signal is sent out by the inside tiny antenna from the C7. C8 is used to add broadband and prevent impact on the frequency from human induction. Actual use proves that it is the essential element. Figure 2 shows the receiver circuit. When the receiver receives the signal sent by the transmitter, the pin ② of IC TDA7000 outputs low level, the music IC CW9300 has no high level to trigger signal and does not work, then speaker BL is silent.