How to build a scalable transistor-based burglar alarm This is a simple transistor anti-theft alarm circuit. Its functions include automatic entry and exit delays-Bell is regularly shut off and reset. It is designed to be used with normally closed input device types such as reed contacts-microswitches-aluminum foil tape-and PIRs. The basic alarm has an "exit / enter" zone and an "immediate" zone. This will be sufficient in many cases. But-large buildings are best divided into smaller areas. The modular design of the alarm means that you can add as many areas as possible to the system. They are "immediate zones"-and can be triggered by two normally open and normally closed input devices schematic diagram It is easy to use. Make sure the green LED is illuminated-then use the alarm bell of switch SW1. You have about 30 seconds to leave the building. When you return and open the door-the buzzer will sound. You have turned off the alarm for about 30 seconds. If you do not do this-Siren will sound. And the trigger of at least one switch is still open-Siren will continue to be sound. But-if the trigger circuit has been restored-the alarm will reset itself after about 10 minutes. Of course-you can turn off the alarm at any time to turn off the alarm. Due to manufacturing tolerances-the exact length of any delay depends on the characteristics of the components in the actual circuit you are using. But-to some extent-by changing the value of R2 to R7 and R9, you can adjust the exit, entry and reset times to meet your requirements. Increased value increases time-and vice versa. If you don't want an "instant" zone-the missing D7, D8 and D9 highways, R12, R13 types, C8 and green LEDs. Stripboard layout Bill of materials X-Grow Led Grow Light,Full Spectrum X-Grow Led Grow Light,Popular X-Grow 300W Led Grow Light Shenzhen Mingxue Optoelectronics CO.,Ltd , https://www.led-lamp-china.com
