How to build a transistor alarm based on a single area
Explanation
The circuit has automatic entry / exit delays-timing bell / siren cutoff-and system reset. It provides for normally open and normally closed switches-and will meet the usual input devices (pressure pads, magnetic springs, aluminum foil tape, PIRs and inertial sensors). Welcome to reprint, this article comes from the electronic enthusiast network (http: //)
If unsafe-the buzzer will sound when you are on the alarm switch. In this case-you should close an alarm such as an open window or door, and check if all the trigger switches are complete-when your alarm buzzer does not sound the switch. Instead-the auto-exit delay will start.
You have about 30 seconds to leave the building and close the door behind you. When you return and open the door-the buzzer will sound. Then you have about 30 seconds of alarm switch off. If you do not do this-the alarm will sound.
The alarm time will be the maximum length of the sound-not fixed. When the cut-off timer starts running, only the trigger circuit has been restored. Although the normally closed switch remains open-or the normally open switch remains closed-Bai Jing will continue to be sound.
If you want your alarm to turn off after 10 minutes-all that is needed is a simple modification of the trigger circuit. Then the moment when the alarm that the timer starts running is activated. The alarm will stop after 10 minutes-regardless of the state of the trigger switch.
Exit delay, entry delay and stop time can be changed by changing R4, R12 and R13 type values ​​respectively. Questions 5 and Q6 ensure that the entry delay and alarm cut-off timers are always required to be fully charged or fully discharged with C7. If you can tolerate slightly less precise time intervals, then leave question 5, question 6, R14, R15, R16, R17, C8.
The sensitivity adjustment of the inertial sensor, set to the lowest value-will activate the alarm. If you are not using an inertial sensor-replace it with a 27k fixed resistor R8. If you don't use a normally open switch-the missing connection between R1, C1 and R2 and C2 is suitable. Welcome to reprint, this article comes from the electronic enthusiast network (http: //)
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