A child lost alarm circuit

Posted on Mar 28, 2007

Children lost a phenomenon often happens, look around, the family should not have brought enormous suffering and economic losses; in addition, also points to unscrupulous child

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traffickers an opportunity to exploit. For this reason, the design of a radio alarm, children or elderly old man wearing a transmitter, guardianship person with a receiver. When a child or aged man leaving guardian (parent or nanny) Ji from 3-4m, guardian receiving the alarm sound, due to the short distance, it can be found quickly, easily lost. The device is particularly suitable for the holiday shopping malls, Alhambra and other crowded situations. The device consists of a transmitter and a receiver, whose circuit and principle is as follows: (1) transmitter circuit transmitter circuit shown in Figure 13-3 2a. When the VT3 conduction, to VT1, VTZ with a positive bias. VT1, VT2 composition self-excited multivibrator start work. Generating a frequency of 1600 ~ 1800kHz frequency oscillation amplitude signal, the Li, L2 and Ct harmonic oscillation frequency selection circuit, c] to adjust the size of the heap transmit signal frequency must be selected in the spring, the magnet antenna out. Wherein Lj, respectively Si-coated wire gauze keys. 80 turns and 40 turns, the tuning capacitor c1 is 5-30pF. The other as shown in FIG. (2) a receiver circuit 13-32b receiver circuit as shown in FIG. Upon receiving antenna Li receiver to the transmitter signal, the L2 and G tuning circuit select remote control signal with the frequency of the transmitter, the received signal is very weak emblem, the VT1, VT2, VT3 multi-stage amplifier, four push sound integrated musical work, due to lower output power, after the last stage VT4 enlarge the loudspeaker Island L work, issued music, remind guardians to find lost children.

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