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Photo sensing Light Alarm circuit

2014-12-17 21:45  
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This be circuit warn when be become dark, or Light sensitive switch. By use electronics part the base is important , be the transistor 2N2926 and AC128. For the light sensor also LDR (light dependent resistor) or a resister quickly the light. When have no the light makes Q1 ,stop work. The Q2 and Q3 then work, It then send current give buzzer utter loud immediately. By circuit arrangement of Q1,Q2 be the character of Schmitt trigger help testify modify analog signal to digital 2 the level well. And help decrease the condition disturbs all with. This is a simple Photo-sensing circuit. When light hits the photo-transistor, triggers the 4011 that drives a loudspeaker.The  LED  voltage is buffered by a junction  FET transistor and then applied to the inverting input of an op-amp with a gain of about 20. This produces a change of about 5 volts at the output from darkness to bright light. The 100K potentiometer can be set so that the output is around 7 volts in darkness and falls to about 2 volts in bright light.

 

Light Alarm 
 

Easy to make and can be very usefull too.