proximity alarm circuit


Posted on Feb 7, 2014

Inverters U1a and U1b are connected in a simple RC oscillator circuit. The frequency is determined by the values of R1, C1 C2 and the internal characteristics of the integrated circuit. As long as the circuit is oscillating, a positive dc voltage is developed at the output of the voltage-couple circuit: C3, D2 and C4. The dc voltage is applied tothe input of U1c-the third inverter amplifier-keeping its


proximity alarm circuit
Click here to download the full size of the above Circuit.

output in a low state, which keeps Q1 turned off so that no sound is produced by BZ1. With C1 and C2 adjusted to the most sensitive point, the pickup plate will detect a hand 3 to 5-inches away and sound an alert. Set C1 and C2 to approximately one-half of their maximum value and apply power to the circuit. The circuit should oscillate and no sound should be heard. Using a non-metallic screwdriver, carefully adjust C1 and C2, one at a time, to a lower value until the circuit just ceases oscillation: Buzzer BZ1 should sound off. Back off either C1 or C2 just a smidgen until the oscillator starts up again-that is the most sensitive setting of the circuit.




Leave Comment

characters left:

Related Circuits

  • New Circuits

    .

     


    Popular Circuits

    General use Preamplifier with 2N3904
    Positive Pulse Pulse Stretcher
    Class A MOSFET Amplifier 2SK1058
    Noise Suppression For R/C Receivers
    Heat Sensor
    AH1751-P HALL EFFECT LATCH
    Feeding CB and Ham radio audio into the aux circuit
    Solid State Tesla Coil/High Voltage Generator
    Whites Classic I metal detector schematic diagram
    The STA013 MP3 Decoder Chip



    Top