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Door open beeper alarm

2016-02-18 20:15  
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When door is opened, the beeper is enabled by the logic high state and the speaker starts beeping intermittently at a rate of about 0.5 secs on/0.5 secs off. Frequeny of this gated aural output is near 450 Hz. After assembling, enclose the circuit including the reed switch, in a plastic enclosure and mount it on the door frame.Door open alarms are used chiefly in automotive, industrial, and appliance applications. This type of circuit can sense the opening of a refrigerator door. When the door opens, a triac could be activated to control the inside light. The figure shows a door position alarm. When the door is opened, an  LED  turns on and the piezo alarm sounds for approximately 5 seconds. This circuit uses a  TL3019  Hall-effect device for the door sensor. This normally open switch is located in the door frame. The magnet is mounted in the door. When the door is in the closed position, the TL3019 output goes to logic low, and remains low until the door is opened.

Door open alarm 
 

This design consists of a  TLC555  monostable timer circuit. This starts the timing cycle. Both the piezo alarm and the LED visual indicator are activated."Door Open" alarms are annoying because they sound all the time the door is open, and Temperature alarms are not much help, because they respond too late.The Alectro Systems Door Alarm remains silent while the door should be open, then alerts you when it has been left open too long.