I have a loose understanding on DC theory, my experience has been mostly with automotive wiring, nothing really with smaller component stuff.. so this all new and exciting to me! I think it is going to be a fairly easy project to draw up, I just have no idea where to start and could use help and direction learning how to calculate what is needed.
What I'm trying to build is a circuit that will turn on 7 LED's via a 3 way switch ( ON / OFF / AUTO ) through a 12V transformer (plugged into the wall so its not battery dependent) that can be dimmed with a potentiometer. When in the ON position , the 7 LED's would illuminate, and be able to be dimmed by the potentiometer, and while in the AUTO position, the lights would turn on via a photocell ( dark would turn on the LED's ) and also would be able to be dimmed in this position.
The details:
Voltage Source - 12V
LED Voltage Drop - 3.5V
Current - 25ma
7 LEDS
I scoured the internet thinking someone would have built something similar, and I found one that was close, however it just modeled one LED and without a potentiometer as a dimmer. Here is one that I found that was the closest to what I was after.
[img]http://img197.imageshack.us/img197/7933/tsr6.jpg[/img]
I bought the components to model this schematic on a breadboard, and using one LED it worked fine. I was able to dim using both ON and AUTO (while using the appropriate 390 ohm resistor in place of the 470 ohm resistor)
The problem is I don't understand it! I don't really understand how the transistor works, and how the values change for the different components as I add more LED's. I don't know if I need to upsize the transistor or if the 1K and the 100K resistor values need to change to make the photocell more sensitive to the light with the rest of the circuit?
Can someone help me take this footprint of a schematic and help me tailor it to suit my needs? I would appreciate it a lot!!
