photoresistor

[matz]

hi der! im a newbie. sorry if i ask stupid questions. heres the situation: im using a photoresistor to control the flow of current on a bulb. but the photoresistor (i think it is also called as LDR or light dependent resistor??) would increase resistance if the light that hits its surface decreases therefore making the bulb's light also dimmer because of the increase of resistance. but i want it to make it in a reverse way, whenever it becomes darker, the light from the bulb would increase. much like on the street lights when it gets dark, they turn on by themselves and as it gets darker, the lights gains more current making them brighter until it reach its brightest. somebody told me to use a transistor to be a switch but he doesnt know what transistor or how the connections should be. pls, pls pls i really need help. could somebody tell me what type of transistor and how the connections would be??? pls guys... tnx in advance!!!


sorry for the long post.

 

[Nigel Goodwin]

hi der! im a newbie. sorry if i ask stupid questions. heres the situation: im using a photoresistor to control the flow of current on a bulb. but the photoresistor (i think it is also called as LDR or light dependent resistor??) would increase resistance if the light that hits its surface decreases therefore making the bulb's light also dimmer because of the increase of resistance. but i want it to make it in a reverse way, whenever it becomes darker, the light from the bulb would increase. much like on the street lights when it gets dark, they turn on by themselves and as it gets darker, the lights gains more current making them brighter until it reach its brightest. somebody told me to use a transistor to be a switch but he doesnt know what transistor or how the connections should be. pls, pls pls i really need help. could somebody tell me what type of transistor and how the connections would be??? pls guys... tnx in advance!!!

Assuming you want the light to come on when it's dark, and go off when it's light (just like a streetlamp) - you need a comparator, or an opamp wired as one. By applying a little positive feedback you can stop it flickering on and off around the switching point, and perform a nice clean switch instead.

 

[matz]

ok thanks!! but wants an opamp? sorry if thats a stupid question.

 

[Nigel Goodwin]

ok thanks!! but wants an opamp? sorry if thats a stupid question.

It's an 'operational amplifier', originally used in analogue computers they are now cheaply available as small I/C's. It's a very common electronic component, it has the advantage of making designing a circuit a great deal easier.

 

[csaba911]

Hi
I think you should check this page, very siple circuit.

**broken link removed**

Steve

 

[matz]

thanks so much. that really did helped. thanks a lot guys.