Light activated switch 2011-09-04

[3lectrix]

3lectrix submitted a new article:

Light Activated Switch - The circuit is based on National Semiconductors comparator LM311 (IC1) and an LDR. The non invertin

The circuit is based on National Semiconductors comparator LM311 (IC1) and an LDR. The non inverting input of IC1 is given with a reference voltage of 6V using resistors R3 and R4. The input to the inverting input will be the voltage across the LDR that is light dependent. At darkness the resistance of the LDR will be high and so do the voltage across it. In this condition the voltage at the inverting input will be higher than the reference at non inverting pin and the output of the comparator...

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[Roff]

Hysteresis can be added by connecting a 100kΩ resistor from the pin 7 to pin 2. 100k may not be the optimum value, depending on the light source. It might also be helpful to connect a 10-100uF cap across the LDR, to filter out hum from artificial lights.

 

[nizam_28jan@hotmail.com]

can you help me create a circuit that consist a motion sensor & led. The objective is the led will light up when the motion sensor detects movement..please?

 

[peterlonz]

I can not understand why I see so many circuits powered by 9V batteries which have low capacity & hold little charge.
Surely 4 x AA's or 6V lantern battery offer lower cost & convenience.
I am a bit disappointed the poster acknowledged relay chattering as a probable event but offered no solution, leaving it to Roff (thanks for the input) to suggest remedies.
Surely the poster might acknowledge & update his circuit?

 

[umarfarouk]

Can you help me construct a circuit that can turn on a light when it is dark,and can turn it off when there is light in the surrronding.i am using a pic P16f84A.may God bless you!