The post explains a GHz microwave radar security alarm circuit which is designed to detect an intruder within the critical zone only while it's moving, static objects produce no effect for the sensor.

Using Doppler Sensor KMY24


In the previous article we learned about a microwave Doppler radar sensor module KMY 24 which is a Hi-end sensor device capable of transmitting a sample signal in the GHz range across the set zone until it's reflected from a moving object back to the sensor for the necessary processing.

In the following discussion we will see how this module can be suitably rigged with opamps for enabling the detected signals to be amplified and fed to an appropriate load such as an alarm or a relay driver stage.

Circuit Diagram




Referring to the above GHz microwave radar security alarm circuit we can see the sensor module KMY 24 configured with the first opamp stage using N1 and the associated components.

Basically N1 is wired up as a differential error amplifier, wherein its two inputs are hooked up with the two differential outputs of the sensor unit.

Detecting a Moving Object


When a moving object or target is detected in front of the sensor module the reflected GHz signals go through a relative phase shift which is reflected back to the sensor and is processed inside the module producing an equivalent positive or negative response across the center two pinouts of the KMY 24 module.

This difference in voltage is fed to the two inputs of A1 which detects this and generates an equivalent amount amplified differential voltage across its output pin#1.

A2 is configured as a filter stage which monitors the output from A1 and filters the unwanted spikes that might be induced at its input and feeds a clean amplified differential signal to the next opamp N3 stage.

N3 is connected as an impedance matching or transforming stage, which processes the fed differential input from N2 and converts it into a distinctive high or low pulses across its output pin# 8, which becomes compatible to be used with either a DC alarm stage, relay driver stage or even a Microcontroller input.

Thus the GHz microwave radar sensor alarm circuit may be used as a security system for detecting even the slightest of movements from an intruder within a 6 meter range from the sensor's emitting point, and convert into an alarm or any desired triggered output.

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