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LDR switch circuit diagrams

This is a light switch or light activated relay circuit. The relay on when LDR uncoverd and relay off when LDR covered. Adjust VR1 for light sensitive. LED will turn on at the same time with relay.
Source: http://www.coolcircuit.com/circuit/light_switch/http://electroschematics.com/wp-content/uploads/2010/07/light-switch.gif (http://electroschematics.com/wp-content/uploads/2010/07/light-switch.gif)

This is the circuit diagram of a light activated switch based on National Semiconductors comparator IC LM 311 and a LDR.
Source: http://www.circuitstoday.com/light-activated-switch-circuithttp://electroschematics.com/wp-content/uploads/2010/07/light-activated-switch-550x343.jpg (http://electroschematics.com/wp-content/uploads/2010/07/light-activated-switch.jpg)

The circuit below shows a simple application of ldr operated switch. This circuit senses the ambience light and depending on the presence/absense of sufficient ambience light, it turnes the bulb On/Off automatically. The bulb gets on when there is insufficient ambience light (e.g evening or night time) and switches off automatically when enough ambience light is present. (e.g In day time, when the sun light is present additional light may not be needed.) This bulb can also be your street lamp that needs to be switched on every evening, and switched off every morning. The circuit does this job automatically without any manual interference.
Source: http://www.electronicdesignworks.com/circuits/light_operated_switch/light_operated_switch.htmhttp://electroschematics.com/wp-content/uploads/2010/07/ldr-operated-switch.jpg (http://electroschematics.com/wp-content/uploads/2010/07/ldr-operated-switch.jpg)

Light sensitive switch with LDR, actually it has a buzzer which will sound an alarm…
Source: http://www.eleccircuit.com/light-sensitive-switch-with-ldr-2n2926/http://electroschematics.com/wp-content/uploads/2010/07/light-sensitive-switch-with-ldr-550x352.jpg (http://electroschematics.com/wp-content/uploads/2010/07/light-sensitive-switch-with-ldr.jpg)

[hadi elec]

Photocell based night light john (http://www.circuitstoday.com/author/john)
July - 9 - 2009
16 Comments (http://www.circuitstoday.com/photocell-based-night-light#comments)





Description.
Many automatic night light circuits had been published here. This one uses a photocell for detecting the light intensity. At full light the resistance of the photocell will be few ten ohms and at darkness it will rise to several hundred ohms. The IC1 uA741 is wired as a comparator here. At darkness the resistance of photocell increases and so the voltage at the inverting input of the IC1 will be less than the reference voltage at the non inverting input. The output of the IC1 goes to positive saturation and it switches ON the transistor to activate the relay. By this way the lamp connected through the relay contact glows. The diode D1 works as a freewheeling diode.
Circuit diagram.
http://www.circuitstoday.com/wp-content/uploads/2009/07/photocell-based-night-light.jpg (http://www.circuitstoday.com/wp-content/uploads/2009/07/photocell-based-night-light.jpg)

Notes.


The circuit can be assembled on a Vero board.
Use 9V DC for powering the circuit.
POT R7 can be used to adjust the sensitivity of the circuit.
The relay K1 can be a 9V, 200 Ohm SPDT type.
L1 can be a 230V,60W lamp.
R8 can be a ORP 12 photocell.