Field-strength meters


Posted on Feb 4, 2014

This circuit, enclosed in a small plastic box, can be placed into a bag or handbag. A small magnet is placed close to the reed switch and connected to the hand or the clothes of the person carrying the bag by means of a tiny cord. If the bag is snatched abruptly, the magnet looses its contact with the reed switch, SW1 opens, the circuit starts osc


Field-strength meters
Click here to download the full size of the above Circuit.

illating and the loudspeaker emits a loud alarm sound. This device can be very useful in signalling the opening of a door or window: place the box on the frame and the magnet on the movable part in a way that magnet and reed switch are very close when the door or window is closed. A complementary transistor-pair is wired as a high efficiency oscillator, directly driving a small loudspeaker. Low part-count and 3V battery supply enable a very compact construction. If the circuit is used as anti-bag-snatching, SW1 can be replaced by a 3. 5mm mono Jack socket and the magnet by a 3. 5mm. mono Jack plug with its internal leads shorted. The Jack plug will be connected with the tiny cord etc.




Leave Comment

characters left:

Related Circuits

  • New Circuits

    .

     


    Popular Circuits

    RF-telemetry transmitter features minimal parts count
    Automatic Headlight Brightness Switch Circuit
    Need Help: Wiring LEDs with 2 source voltages
    Led Running Lights
    pippin qrp transmitter
    converter lhc4 6 8ka 08v
    gsm gps based vehicle theft control
    wireless microphone circuit
    general purpose alarm
    1.2GHz VCO With Linear Modulation circuit using MAX2754
    Video Amplifier
    Logic Probe Circuit Schematic Diagram
    Shortwave Monitor
    Laser Pointer Remote Control Circuit
    Circuit having a high school bass tone function



    Top