efiste2

Hi, its been a long time since i built basic circuits at college and recently my son has started a very basic circuit project in his junior school class, so i thought we would give him a head start, by showing him the basics ac/dc switches resistors etc etc, but i came across an LDR( light dependant resistor) in my bits and bobs box and we tried to build a simple "light that comes on when it gets dark circuit" with the LDR, an LED etc etc, but what i cant remember is that how we used to build this very basic circuit, so heres my first of probably mane newbie questions..... the resistance of the LDR goes up as the light fades and vica versa. obviousley this only allows the LED to come on in daylight etc etc, so how do i configure the LED and LDR to work correclty, the value of the LDR i have is ......in bright light the resistance is 1k and with no light the resistance is 20k

bananasiong

Use a LDR, a variable resistor, a BJT, a resistor and a LED.

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House0Fwax

Have a look at this site;
http://www.technologystudent.com/elec1/opamp3.htm

It explains how its done.

efiste2

thanks, i thought id have to use a transistor........................