light sensor.

I'm a little confused why you're using a transistor to drive a relay. Transistors only amplify current, not voltage. Relays are triggered by voltage, not current.

The base of the transistor is grounded. This will achieve nothing

http://everycircuit.com/circuit/5859248225386496

Basically to simplify this whole circuit, delete the transistor - not needed for this type of application, connect the LDR to the relay. Adjust relay settings so that it opens at 2V and connects at 10V depending on what you desire as far as light sensitivity goes.

mwilliams, your last suggestion is entirely the Wrong way to go about it. Adjusting a component's value to suit how you want a circuit to work is conceptually flawed, as that is not at all how things happen in real life. By doing this a person learns nothing but a bad habit! okrk- the latest circuit I've published is one you should have a look at. I wrote a long description, and did so in hopes of helping someone with what you're asking for now. Take a look at it, I hope it provides you with some information. To see it, click my screen name, in the next window click "list", and then "recent". You should find it there at the top..

I used transistor cause of ldr. I have checked out Sine_eyed projects but couldnt see what i need

Check my circuits, if you are still searching!