Awesome, thanks a million.
I want the LEDs to increase in brightness when the photoresistor is hit with more light (light activated, I guess).

I'm assuming the potentiometer and LDR in the diagram are representative of 1 photoresistor? So then I just need to figure out the resistance range of the photoresistor and adjust my LED resistors accordingly?

The photoresisor's resistance varies with the light intensity. You cannot physically adjust the resistance of the photoresistor aside from manually placing a foxed brightness light source in front of the photoresistor. It's not critical to know the range. They can be as little as 50 ohms with bright light and many MegOhms in darkness. The adjustable resistor however is used to pinpoint at what light level the LED's will turn on and is normally done by trial and error.

Also, would one lead of the photoresistor be connected to the base of one NPN, and the other lead connected to the negative lead of the power source? I understand how to wire the LEDs, resistors, and transistors, just not the photoresistor.

Thanks again for everyone's help so far. Sorry I'm so newb at this.

For your application, LED's on when photoresistor sees increased light, you would use the third circuit provided. This would mean that one lead of the photoresistor is connected to the positive source, the other to buth the transistor base and variable resistor.

 

Your circuit wont work. To make it work make a voltage divider with the photoresistor and a variable resistor (as to vary the sensitivity). Remove q1 and connect q2 emitter to ground. Finally, connect the voltage divider output to the base of q2. Also, put a 1K resistor between the base and the output of the voltage divider.

 

Looking more like it?
And, are my r1 values going to be the same as if I wired just the LED grid to the 9v power alone (68 ohms)?

 

Yes. I dont know how the resistance of the photoresistor varies (increase or decrease with increasing light intensity) but if it acts like a dark detector just switch the position of the photoresistor and the variable resistor.

 

Excellent
Thank you all for being patient with me and so helpful. I'll throw up some pics and possibly a vid of the finished product when its complete.
Thanks again,
RobW

 

Hello everyone,

My project (7-segment LED gear indicator for my motorbike) needs the same knowledge, I have learned a lot from your posts. I would like to increase display brightness in sunny conditions, and decrease in darkness. Unfortunately I could not buy a photoresistor, I have bought a phototransistor instead (BP103-2). How should I modify the circuit to fit this?

Peter

 

Hello RobW,

I would place a little resistor of say 470 Ohm in series with the potentiometer.
This to protect the photoresistor from burning at low resistance.

Greetings,
Bertus