Infrared Alarm System. Design Note. 19

IR-LED-PairThis design note explains how to design an invisible alarm system easily. Infrared Transmitter ( Tx) and Receiver ( Rx) LED pair is easily available which can be used for making this alarm system. Infrared transmitter LED emits infrared rays in the wavelength around 950 nm. This LED is a high current device that can handle more than 100 mA current. The IR receiver LED is a kind of Photodiode that generates a Photo current when it receives IR rays. So the IR LED pair is ideal to make an alarm system that operates both day and night.
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Hall Sensor. Design note 8

Hall sensor is a device that generates output current based on the magnetic field in its proximity. When a current carrying conductor is placed in a magnetic field, a voltage is generated perpendicular to the current and the field. This phenomenon is called as Hall Effect. The Hall sensor has a thin semiconducting material called Hall element. A current is passed through the Hall element in a direction perpendicular to the output connections. In the absence of a magnetic field, current distribution is equal without any potential difference across the output. When a perpendicular magnetic field is applied, a force called Lorentz force disturbs the current distribution and a potential difference develops across the output. The output voltage is called as Hall voltage (VH ). Lorentz force is the force acting on the moving charge carriers in a magnetic field.
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