I'm completely new to Arduino and having ordered my board can't wait to do some experimenting. My first project is to add LEDs to my son's toy kitchen. It would have up to 8 LEDs and 3 magnetic switches. The idea is to lit a led or two when oven / microwave / cupboard door opens. Once that mastered I want to add photo sensor so the whole thing lights up when it gets dark, the last bit would be adding remote control to control LEDs but let me ask you probably a silly question first. When connecting series of LEDs to breadboard each LED positive leg is connected to Arduino pin and negative to GND - of course there is resistor between. GND is connected to one of the lines on breadboard so every LED's negative leg is connected to that line. I won't be using breadboard - each LED would be soldered to a resistor and then connected to specific pin on Arduino. Am I understanding it right there will be one wire connected to GND and all the negative connections (from LEDs and magnetic switches) would be connected to that single wire ? Am I thinking right ? I don't want to fry my board by doing something fundamentally wrong. I know is must sound silly to you but I seriously am newbie here :) Thanks for your help.
In elecrtical circuits you will always have a complete path from and back to your supply. You can do this by running a seperate loop for each device or you can run one common wire around your project usually the earth.
This is because in electrical cabinets and say vehicles they are made of metal and it is easy to wire the earth to the cabinet but this was done for several reasons one being reduces expense. Did you know that there were posative earth vehicles around pre 1990? Use to be hell fitting new stereos to them
For this project you will find it easier to fit the leds to the end of some speaker cable, cutting one leg of the led shorter and fitting the resistor in its place then connect the wires and cover with heatshrink.
This way when they exit the doll house you will have one wire set for each led. You can then connect the earths to a buss bar or earth strap making them all common and connect that to the Arduino.
Beware! Check the Arduino specks and make sure you do not overload it when you have all the leds running and check the max each pin can provide so as to know what resistor value you need.
Once you have the setup going you can experiment with dimming the leds you connect to the PWM ports on the Arduino but first just start with ON/OFF.
Also keep in mind that if fitting even the smallest led or the wiring into the house is a problem, move the led elsewhere and run a fibre optic cable in its place. Takes a bit of fiddling to fit the led to the fibre but is sometimes easier to run a cable that is 0.5 mm thick from start to finnish.
Control panels with on/off and dimming knobs fitted to an external control box are fun to although i have heard of people building working minature light switches.