Need help related to building a potential divider using an LDR

[omarko]

anyone over here who can help me out building a potential divider using an LDR and few LEDs...

Do I need to connect a transistor switch in the potential divider?

I am using a 9V battery, 1 fixed resistor of 1k or 10k ohms, 1 LDR and some LEDs.

I am using this circuit:

In which Vout will be 2-3 LEDs.

I am confused whether to use a Transistor or not :S

 

[ahmedleo]

I don't see why you need to use a transistor, unless you need switching skip the transistor.

 

[omarko]

If it won't switch... wont there always be current running through the LEDs?

I searched a lot on google... har jagah transistor hai :\ WHY?
[MENTION=1283]hasanJ[/MENTION] engineer sahab bata do

 

[hasanJ]

If it won't switch... wont there always be current running through the LEDs?

I searched a lot on google... har jagah transistor hai :\ WHY?
@hasanJ engineer sahab bata do

Explain it to me a bit

U want to make Voltage Divider to power 3V LEDs from a 9V Source and u want its operation to be dependent on LDR?
Transistor is absolutely needed in this case

 

[AbbY]

What exactly are you trying to achieve :S

 

[omarko]

What exactly are you trying to achieve :S

To build a darkness detector.

@ topic

so I ended up using the transistor. I don't know why, but it made my LEDs turn on in the dark

 

[hasanJ]

To build a darkness detector.

@ topic

so I ended up using the transistor. I don't know why, but it made my LEDs turn on in the dark

good to hear

u can invert this function if u want

 

[omarko]

good to hear

u can invert this function if u want

Yes, but then I will have to connect the LEDs along the other resistor instead of the LDR.

Used a breadboard, did not bother soldering and the varroboard.

 

[hasanJ]

Yes, but then I will have to connect the LEDs along the other resistor instead of the LDR.

Used a breadboard, did not bother soldering and the varroboard.

can u post a rough sketch of circuit?

 

[omarko]

can u post a rough sketch of circuit?

ummm I could try taking a picture or scanning the circuit...

ill try gooling first.

And yes, google delivers.

This is pretty much of what I made:

Dark light sensor | Flickr - Photo Sharing!


EDIT: I could try uploading a video I made, too.

 

[hasanJ]

ummm I could try taking a picture or scanning the circuit...

ill try gooling first.

And yes, google delivers.

This is pretty much of what I made:

Dark light sensor | Flickr - Photo Sharing!


EDIT: I could try uploading a video I made, too.

If u dont minde
try switching the position of 100k Resistor and LDR

 

[omarko]

If u dont minde
try switching the position of 100k Resistor and LDR

How will that help me?

I mean, the circuit is working perfectly. As in, when light intensity decreases on the LDR, more potential is drawn on the LEDs... and they light up...

Vice versa in roshni/light.

 

[07ee17]

How will that help me?

I mean, the circuit is working perfectly. As in, when light intensity decreases on the LDR, more potential is drawn on the LEDs... and they light up...

Vice versa in roshni/light.

It'll make it a Light Detector. Meaning that LED will turn on when there is enough light in the room to lower LDR resistance below a certain threshold. When there is dark, LDR resistance will increase, and transistor will turn itself OFF, hence turning LED off.

 

[omarko]

It'll make it a Light Detector. Meaning that LED will turn on when there is enough light in the room to lower LDR resistance below a certain threshold. When there is dark, LDR resistance will increase, and transistor will turn itself OFF, hence turning LED off.

Yes, you are right.

Thanks.