To use the IF signal in most practical applications, you need a “conditioning circuit” or an amplifier, basically, that makes the level high enough to be able to then send it to the ADC of a microcontroller (such as the Arduino one) or to a voltage comparator that switches its output based on the exceeding of a threshold that we can consider both that of alarm and which in practice would correspond to the size or reflection capacity of the body in movement, as well as the speed of movement of the body itself. 2 and allow to understand which are the optimal detection areas of the radar. The irradiation diagrams on the horizontal and vertical planes of the RF waves are shown in Fig. generated by the local oscillator) and the received frequency, the latter dependent by various factors such as the mass and the speed of movement of the body on which the reflection takes place (target) and more. The IF signal is therefore the one that gives us the indication on the detection of something moving in front of the sensor and exists only when there is a difference between the frequency transmitted (i.e. 1 ) which also contains the microwave antennas. The electronics are enclosed on the front by a metal cover ( Fig. The sensor to which we refer is the popular HB100 (produced by Agilsense, which is a device made on an SMD printed circuit, containing an oscillator that emits microwave from a special antenna pointed at the front and receives from an antenna receiver, mixing the two signals in an RF mixer and thus exploiting the Doppler effect. In the past we have already dealt with microwave sensors, using a dedicated breakout board in the corresponding project (the corresponding article is the one published in the file n° 227 of July / August 2018) and today we want to return to the topic by proposing a new project developed around a powerful radar operating in the X band and precisely at 10.525GHz (this is the typical frequency, but the sensors marketed in Italy usually operate at 9.9 GHz), capable of detecting the movement of people and objects in their range action. Now the devices used in presence and movement detection systems, to be combined with automations for opening doors and turnstiles but also with anti-theft and anti-intrusion systems, stand out passive infrared radars (otherwise called PIR) and microwaves, which, compared to the first ones, have the prerogative of being able to detect even just the presence, but above all to be able to do so even if the person or object is behind walls and doors, provided that they are not made of metal or contain armor metal. Motion detector based on the Doppler effect, made by combining a specific sensor with a circuit that amplifies the output signal.
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