Light alarm schematic circuit diagram

  
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This light alarm schematic circuit is designed using some common electronic parts, as you can see in the circuit diagram bellow. This light alarm schematic circuit project will sound as soon as the drawer is opened and light falls on the Darlington phototransistor. The output alarm may be redesigned to activate a relay or triac. The 14011 quad,
Light alarm schematic circuit diagram - schematic

2 input, NAND gate is wired up to oscillate when the input to it goes high, that is the BC557 transistor turns on after light is detected by the MAL12. After the alarm has started and it is put back into dark conditions, alarm will continue to sound for about 3 - 5 seconds. This is due to the 1uF capacitor and 4M7 resistor which keep the input to the 14011 high.



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