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

    LED Countdown Timer with AT89C2051
    AM Broadcast Transmitter schematic
    amplitude modulator
    Sonic Defender
    Digital Automatic Level Control (Alc) Circuit
    555 circuits 6
    relay Do I need a protection diode here
    Simple IR audio link
    Frost Alarm
    Low Resource Microcontroller 3 Phase BLDC Motor Speed Controller
    Electronic thermometer
    SW Receiver Using ZN414



    Top