For Random application Simple Door Open Alarm circuit using hall effect sensor designed with timer IC 555, it can detect open door and produce loud alert sound through 0.5 watts loud speaker. This circuit utilize A1302 Hall-effect sensor IC and it is optimized to accurately provide a voltage output that is proportional to an applied magnetic field.
Here timer IC 555 is configured as Astable multivibrator and Reset pin is connected to the output pin of Hall effect sensor A1302, whenever the magnetic field removed from this sensor then near Vcc voltage appears on output pin.
- Timer IC 555
- Hall effect Sensor IC 1302UA
- Loud Speaker 8Ω/0.5W
- Resistors 100Ω, 1KΩ, 51KΩ, 43Ω each one
- Capacitor 0.01uF, 0.04uF each one
- Capacitor electrolytic 33uF/16V
- 9V Battery
- Small Magnet
Construction & Working
In this circuit hall effect sensor acts as a Switch and Timer IC 555 circuit acts as a Pulse oscillator and during near magnet situation (closed door) hall effect sensor acts as open switch and there is no voltage at Reset pin 4 of timer IC 555. During far from magnet situation (opened door) hall effect sensor acts as closed switch and gives output voltage near Vcc and hence the Reset pin 4 gets bias (we know Reset pin 4 of IC 555 is active low pin) and timer IC starts to Oscillate pulse signal.
Timer IC 555 is employed as Astable multivibrator and output is connected with 8Ω / 0.5 watts loud speaker, Output pulse duration is depends on timing Resistor R2, R3 and timing Capacitor C1. By changing these value we can get different alert sound tone from loud speaker.
Place the Alarm circuit with power supply battery above the door frame and make sure the expose hall effect sensor A1302 to Magnet attached with door when the door is closed.