Radio induction alarm circuit

Circuit composition The inductive anti-theft alarm circuit consists of a radio scanning detection circuit, a signal processing circuit and an alarm circuit, as
shown in Figure 13-43.
    The radar detection circuit consists of the radar detection module
(including microwave emission, low-pass filtering,
gate amplification and other circuits) IC1, antenna W and
inductor L.
    The signal processing circuit consists of the identification amplification module
IC2 (including voltage stabilization, strobe amplification, soft
start, comparison amplification, delay drive and other circuits
), capacitors Ci, Cz, resistor R.
and potentiometer RP.
    The alarm circuit is composed of resistor Rz, transistor
VT, diode VD, relay K and
alarm HA.
    (2) Alarm principle The microwave oscillation signal (about 1000MHz) generated by the oscillation circuit inside IC1 is transmitted to the surrounding space through the antenna W Emit
high-frequency electromagnetic waves. When there is no object moving in the radar scanning detection area, the control output terminal (0 terminal) of IC2 outputs low level, and VT is in a cut-off
state. K is in a released state. HA is silent.
    When someone moves within the effective control range of the radio scanning detection circuit, the magnetic field in the space will change. Antenna W sends the detected human
body movement sub-echo signals to IC1 for low-pass processing, causing the signal output terminal (O terminal) of Ic1 to output an ultra-low-frequency signal. This signal is
further gated, amplified and delayed driven by IC2. A high current is output from its control output terminal, causing VT to conduct, the relay K to close, and HA to energize
and emit a loud alarm sound.