Four Light sensor alarm circuits

These are four light sensor alarm circuits, 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. The detail is other , see in the circuit.

Circuit Light Sensitive Switch with LDR + 2N2926

Active light control by LDR and BC337

This is automatic light circuit when be become dark. It by use LED Lamp, be a place gives the light and this circuit has small-sized use volt supply 3V only.
The work of the circuit be when there is the light affects LDR1 will valuable the resistance at LDR1. It be down make Q1 work be born volt at fall straddle a pin C of Q1 compare with Ground be valuable a little more voltage bias to make Q2 work. By have D1 serial with a pin B of Q2 make volt at pin C of Q1 compare with ground must use volt about 1.4V arrive at make Q2 work. But when LDR1 no the light will make to is valuable the resistance more and more until make to have no current flow get along well with B of Q1 make Q1 do not work. Then have current flow through R1,D1 get along well with pin B of Q2 work cause LED1 stick bright. The part , VR1 , parallel connection with , LDR1 , as a result , for take keep fine the rapidity in taking light of LDR1

Opto-Tone (Control sound by light

The Opto-Tone (Control sound by light) circuit with IC 555 and sensitive light by LDR.
Opto-Tone (Control sound by light)

Light Dark Detector Alarm by IC 555

Today we come to see the circuit detects the light by have a voice warn. When meet the light or be become dark depend on using S1 ( follow the circuit ). For this my circuit uses the integrated circuit IC 555 be pillar equipment again. You can choose can use many the number be LM555 or NE555 or use the number instead of eat the low beam be IC 7555 all right. For that circuit when S1 stay in a position . And there is the light shines at LDR (Photoresistor) a loudspeaker will utter. When S1 stay in a position and have no the light at LDR loudspeaker utter also. This easy good circuit friends may have fun IC 555 detector light this please sir.
Light Dark Detector Alarm by IC 555


  1. nhlanhla February 28, 2013
  2. kiril popov October 10, 2014
  3. innocent October 31, 2014
  4. domenick February 3, 2015
  5. momename February 3, 2015
  6. rajpri May 21, 2015

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