PROXIMITY_ALARM_I

Published:2009/6/17 21:08:00 Author:May | From:SeekIC

IC1 contains several oscillators and an amplifier. The low-frequency audio-signal oscillator is used to supply an input to the amplifier. That signal is the audio tone that is amplified, then supplied to the speaker by the amplifier.The high-frequency oscillator is purposely set to be very unstable. It is dormant or off until the resistor-capacitor (RC) network is changed. The resistance (fi) in this case is made up of R2 and P1. As the resistance of Pl is decreased, the unit becomes more sensitive (more unstable), and less ca-pacitance (C) is needed to cause the oscillator to oscillate.The capacitance required is provided by C2 and by any capacitance introduced via the antenna loop. When you come near that loop, your inherent body capacitance causes the high-frequency os-cillator to begin to oscillate, which then causes the low-frequency oscillator to be switched on in-ternally. Once the alarm is sounding, the IC is designed so that it latches , that is, it stays on until the power to it is switched off.C1 1-pFAxialCapacitorC2 27-pF Silver Mica CapacitorC3 0.1-pF Mylar CapacitorIC1 CM1001N ICP1 50-kQ Trimmer ResistorR1 75-kQ ResistorR2 200-Q ResistorR3 100-kQ ResistorS1 SPDT SwitchSpk Small SpeakerMisc IC Socket, Battery Snap, Ground Plate, Wire, PC Board



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