Door Sensor – Working & Its Applications

• A sensor and a magnet are used to operate a door contact sensor. When the sensor is in close contact with a magnet, an internal reed switch on the device closes. The magnet and sensor are separated when the door is opened. The sensor notifies the panel as a result, releasing the reed switch.

• The first component is attached to the door frame, and the second piece is parallel to the first piece and is attached to the door. When the door is closed, the two components form a closed circuit. The magnet and switch separate as the door opens, interrupting the circuit. The sensor alerts the central control panel when the circuit fails.

Working of Door Sensor

Door sensors are very simple and easy to design, they can be designed using various circuits, one of the circuits is shown below,

• The circuit is straightforward to operate. The mechanical design places the bar magnet very close to HS1 (MH183) when the door is closed, turning it on and disabling the first oscillator created by the two gates (A & B) of IC1 as a result (CD4093-Quad 2-Input NAND Schmitt Trigger).

• The consistently lighted red LED serves as a signal for this situation (LED1). Keep in mind that the relaxation oscillator, which is connected to one of IC1’s gates (D), is here pulsing LED1.
• However, because of the relatively high frequency (determined by C2 and R5), LED1 appears to be on all the time. The LED current is constrained to a safe level by resistor R6. The door opens, and the magnet departs from IC1. Through resistor R2, the Two-gate oscillator (IC1A & IC1B) is now enabled as HS1 is turned off.
• To gate the LED oscillator (IC1D) on and off, IC1C inverts the low-frequency pulses from this oscillator.
• The circuit should be assembled on a tiny PCB and enclosed in an appropriate enclosure. Fix the magnet on the door while maintaining its south pole’s (S) direction toward the designated side of the Hall sensor (HS1), which is fixed at the corner of the door frame. Place the magnet and Hall sensor in such a way that LED1 illuminates steadily when the door is closed.

Applications of Door Sensor

Door sensors are used for truck door fleets to

• Preventing cargo theft.
• Protecting refrigerated loads.
• Reducing energy and food waste.
• Minimizing the costs associated with load loss.

Door sensors are an essential component of your home security system: they let you know when someone is entering your home.