Hi
I want to build a Fan that turns on when it reaches a certain temp. But i have one question is it possible to use the arduino as a switch.
What i mean is can i program the arduino to turn on the fan (HIGH) when it reaches a temp, or would i need a relay or transistor?
Are we talking about a little tiny fan that you might cool a cockroach with or a big one that you need to provide a 24 hour warning to the power company before you turn it on? Are we talking one that uses DC or AC power? Makes a wee bit of difference. A specific link with datasheet might be nice to provide.
Most micros like the Arduino can only supply a handful of milliamps at voltage. Unless your fan is very small, you will need something to switch the power. What that something is, will depend on what you need to supply. It might be as simple as a small transistor, or as complex as a contactor. http://en.wikipedia.org/wiki/Contactor
I am talking about a small fan but i do not want the arduino to power it i just want it to turn it on and off
What has this got to do with PIC Microcontrollers - Software and Hardware?
jped:
I am talking about a small fan but i do not want the arduino to power it i just want it to turn it on and off
If you want the micro to control the fan but not power it, then by definition you need something like a transistor, FET, or relay to control it.
The next step is to learn what voltage and current the fan uses. With this information one can design an implementation.
Again, a link to the specific fan or at least one that is very similar would be helpful.