Photo resistor to turn a led on/off?

Hi, can I use a Photo resistor to turn a led on/off?
I'm looking at other projects and I see people tearing apart motion detector kits.
Can I just link up a photo resistor, 3v button battery and a LED in a series?
I want this to be as small as possible so I can't use any of those arduino things.

I just need the LED to either turn off or on when something is near it, I just want a reaction.


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Better to use a transistor too. You won't get "on/off" really, but a gradation from on to off depending on the resistance.

RoboRay (author)  steveastrouk5 years ago
Thanks, how should I connect the transistor? and what time should I get? I'm not an EE so I don't know much about these things.

Here's a circuit to play with: You'll have to play with component values. One of the two resistors connected to the base should be your photoresistor. The resistor connected to your LED is determined by the supply voltage.

Try and find a "Darlington" transistor.

RoboRay (author)  steveastrouk5 years ago
Thanks for the Drawing. I just came back from radio shack and they had no idea what a Darlington transistor was. They just pointed me to the parts box and showed me the transistors. There were so many types there and I had no idea which one would work. I saw some bi-polar and switching types.

Could you help me pick out the transistor on the radio shack site?
I plan to use this photo resistor since this is what they carry.

I also only have 150ohms resistors on hand.
It will be powered by a 3v button battery.
Try the TIP120.

RoboRay (author)  steveastrouk5 years ago
Hi, I built this today and is there a way to make the led brighter in low light? thanks
Brighter than it is in bright light ? What current is in the LED.
RoboRay (author)  steveastrouk5 years ago
I don't know the LED's current. but I am using 3v batteries. without the photo resistor, the LED is very bright. I just need it bright enough to show through a thin plastic sheet.
would making it brighter require a micro controller?
What resistors did you use in my circuit ? What is the resistance of your photo resistor in dark and light conditions. You don't need a microcontroller, yuo just need to play with the resistor values you've used.