Simple Light and Dark Detector 

+Elecnut Thank you for watching and providing this inspiring comment.

Thanks! Hope you had fun with it.

Bilader bende olmuyor ya yardım etsene

Risister value

+CHANDANA CHOUDHARY The resistor in the second circuit is doing two things: limiting the current through the LED and programming the the voltage divider to light the LED when the appropriate conditions are met.

No, the LDR should be ok as long as it does not get hot during operation.

You can drive both with a transistor.

I used a 9 volt battery.

A transistor version will be more sensitive.

No. At 0:34 the text mentions the resistance is 330 ohm and at 2:09 the text mentions the resistance is 2.7K.

The following is a link to the schematic for an LED-ON when dark. You may need to adjust the resistor value for your particular photocell. www.circuitlab.com/circuit/295y86/led-voltage-divider-light-off/

Thank you, for answering, and so quickly as well. It works a bit better now. Like you said, I have to find the correct value for r2. If I may bother you again, how do I adjust the value for r2, if I'm not sure what value the LDR is?

Photocells come in all different resistance ranges but once you adjust it for your particular photocell it should work for that type. During normal lighting conditions if the LED is ON increase R2 until it just turns off. Turning off the lights should turn the LED on since the photocell resistance and voltage across the photocell increase. Different color LEDs will also change the behavior since Red LED's require less voltage to turn on then Green LEDs. A transistor version works better but I like to keep it simple - at first - as an exercise for my students. I make them calculate the proper resistor values for both circuits based on the photocell resistance and the LED forward voltage. Have fun.

The following link is a video I produced for the procedure for making an LED-On-with-light photocell circuit ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-JWKVgTOgm0Y.html

We are using the non-linear properties of LEDs to make this work and under certain conditions the LEDs are being driven with very small currents to make them light. A transistor can increase the sensitivity by being able to react to much smaller changes in voltage and resistance, drive the LEDs with higher currents and create a better snap-on effect. I originally created this project to help my students understand how voltage dividers work. Using LEDs in the lab makes it a little more interesting and challenging.

Thanks.

The video is 4 years old so that would be difficult. What are you specifically looking for? Maybe I can explain the situation.

Dorian McIntire well, I tried this circuit on my breadboard with an N2222 transistor and it didn't seem to work. I can't really set up circuits from schematics so I was trying to make sure I put everything in the right place. Could it just be my transistor?

This circuit does not use a transistor. It just uses a photocell , resistor and LED. Another video can be found at the following link: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-JWKVgTOgm0Y.html

9 Volts