One of capacitive sensing oscillator circuit burglar alarm

  
By the 555 IC Ai, capacitors Cl, Cz and metal plate (tablet) M distributed capacitance Co and resistor Ri to ground, R2 consisting self-excited multivibrator; the R3-Rs and C3
One of capacitive sensing oscillator circuit burglar alarm - schematic

~ C5 composition three -order RC integration network; by the CA3130 operational amplifier Az, Re, R7 and RPi, RPz composition comparator; by the transistor VT and R8, R9 composition amplifier. When the body close to the metal plate M, Co capacitance increases, the multivibrator oscillation frequency decreases, RC network outputs a negative pulse, VT conduction, the relay KA pull, turn alarm, an alarm signal. Adjustment potentiometer RPi, RP2, can change the sensitivity of the device.




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