So basically I want to be able to flash a bright light on for 3 seconds, off for 10 seconds, etc. for 25 times every day and record the reaction of animals in a tank via webcam. Icing on the cake would be also having a red LED illuminate for the duration of these trials so that the experimenter could see what was going on. Right now I'm controlling the webcam separately with the computer, which is fine since I don't need to automate everything (not having to flip a switch at 10 second intervals manually is already a HUGE improvement in quality of life). I got my arduino uno to run this simple program for a white LED, and separately hooked up another red LED to the 5V power with a resistor to be on continuously, but I decided that my white stimulus needed to be much brighter. So I purchased a 12V DC 54 LED car interior dome box lamp light (sorry, it hasn't arrived yet so I don't know how much current it draws). These are the ideas I've come across for stepping up the voltage, and I'd like to ask people's opinions on which would be the best/ simplest for my purpose (all involve of course hooking up the Ardunio Uno to a 12V power supply).
A logic-level gate MOSFET (can anyone recommend a specific one? Or will I need the current information first?).
A 4N35 optocoupler - Seems to be overkill but it sounds like others have gotten 12V out of an arduino with this method.
A Darlington Transistor Array like ULN2803 - Again, probably more than I need, but I'm willing to go for whatever will work best.
Probably not even worth asking about powering directly from the VIN PIN...
A 4N35 optocoupler - Seems to be overkill but it sounds like others have gotten 12V out of an arduino with this method.
Well you can control 12v with a arduino, using that. An Arduino can never directly output 12vdc. Anyway, most opto-isolators cannot switch much current on their output transistor side, certainly not enough to power your LED assembly. There is a difference between controlling a power circuit and suppling power to a circuit. Arduinos are good at controlling stuff, powering stuff, not so much. Your +12vdc power source will supply the power, your task is to choose what method to use so the arduino can control that power on and off to the array. Most uses of optos are so that subsystems don't have to (or can't) share a common ground connection, and of course for isolating high voltage input circuits from arduino type logic systems.
A Darlington Transistor Array like ULN2803 - Again, probably more than I need, but I'm willing to go for whatever will work best.
The MOSFET is simpler to use in my opinion, but ULN2803 could work possibly by parrelling output and input pins. The ULn is more useful when switching multiple loads independently. You just want to switch the large LED array on and off, correct?
Probably not even worth asking about powering directly from the VIN PIN...
Total current avalible at the Vin pin is one amp or less, due to the series polarity protection diode. But the fact that your LED array requires +12vdc, I would plan on powering the arduino board from the same +12vdc voltage source, either through the external power connector, or the Vin pin, double check your polarity wiring if directly wiring to Vin pin.
So your first order is to get a handle on the current draw requirement for the 12vdc LED array, and then get a +12vdc power supply rated at maybe 50% above that. If on a budget a modified PC power supply could work just fine.