Finnius:
- I want to use the Arduino and a 2N2222 transistor to switch a camera on/off switch. The camera will be ran off the 5v arduino pin - no info on how many mA it uses but it has a 220mA battery...
What resistor will i need for this transistor?
I don't know exactly aht it is you're switching but 330 Ohm should work. The resistor is mainly there to prevent the Arduino pin from letting more than 40mA out so the exact value isn't critical.
Finnius:
2) I am also going to run a 350mA 1W LED off the 5v arduino pin and want to switch it on/off hopefully with a TIP120 transistor from the arduino. What resistor will i need for this transistor?
Again, the resistor value isn't critical. The TIP120 is a Darlington so it has masses of gain. 330 will work here, too.
Finnius:
Also, i read that the 5v can supply up to 1A so 350ma LED should be fine right - will it draw the right amount of current it needs to run/ i dont really know anything about led drivers.... I worked out i would need a 10ohm for the LED
Running a power LED at full wattage with just a resistor is very risky. Even a tiny error in voltage can have big consequences for amps.
If it's an eBay LED it's going to get HOT at full rating. eBay ratings are absolute maximums, not recommended working values. Keeping it cool will be a big problem.
In my personal experience it's much better to buy something like a 3W LED and run it at 60% power. The heat will be far more manageable.
Also: At that point on the LED power curve a small error in voltage isn't critical so if power efficiency isn't an issue you can get away with running it on a resistor (but make it a 10W resistor...)
Finnius:
On top of this, i have read on the net that some people don't use resistors with transistors and it worked fine - whats going on!
What's going on is that AVR chips are very robust and can survive a lot of abuse.
OTOH a resistor costs a couple of cents and can save you from buying a new Arduino.