Auto Alarm

  
SI is external key switch. The alarm allows a 0- to 45-s delay after SI is operated before the circuit is armed. During this per
Auto Alarm - schematic

iod, LED1 lights green. After this delay, LED1 lights red, which indicates that the circuit is armed. Then, sensors S2 through S4 -(NO) or S5 through S6 (NO) pull pin 2 of U2 low, which activates K1 and sounds the alarm. The alarm sounds for a duration determined by R4 and C2. After this time, K1 releases and the circuit is again ready. Manual reset is via the key switch, SI.




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