Pyroelectric Infrared Sensor in Smart Homes

Pyroelectric human Infrared Sensors are sensors that convert infrared rays emitted by humans or animals into electrical signals. It can be used to detect the presence of the human body and is widely used in electronic products such as security devices, burglar alarms, sensor doors, automatic lights and smart toys.

Pyroelectric Infrared Sensors can detect infrared rays emitted by the human body, while the detection distance is close, usually within 2 meters. In order to increase the detection distance, a Fresnel lens is usually installed in front of the light-receiving surface of the pyroelectric motion sensor, and the lens can be detected. Then the detection distance can be more than 10m.

The Fresnel lens is usually made of transparent plastic and the lens is divided into equal parts according to a certain manufacturing method. The plastic Fresnel lens has two functions: one is to focus the light and the other is to divide the detection area into several bright and dark areas. When a person enters one of the bright zones of the detection area, the infrared light emitted by the human body is partially focused by the corresponding lens in the bright zone, and then irradiated to the sensitive element through the filter of the sensor, and when the person walks into the darkness, the sensitive element generates voltage. When in the area, the infrared light from the human body cannot reach the sensitive element, and the voltage at both ends of the sensitive element will change, that is, voltages at both ends of the sensitive element will change with the presence or absence of light. The changed voltage is amplified by the FET and output, the frequency of the sensor output signal is related to the speed of the person moving between the light and dark areas within the detection range. The faster the movement speed, the higher the output signal frequency. If the person does not move within the detection range, then the sensor outputs a fixed voltage.