I'll start with a stupid question:  If USB provides +5V power, why does the DC power input jack need 9-12 V?  Won't the 78M05 voltage regulator burn most of that up?

Next question: I'd like to get an Arduino running off of batteries (efficiently).  Once I had things working on the Arduino USB, I thought I'd pick up an Arduino Mini (aka the Arduino Stamp) and use it with some sort of switching voltage regulator.

If the Arduino USB typically uses 50-100mA (mentioned in this thread), should I expect the Arduino Mini to be much lower?


Thanks!  This little Arduino has my brain spinning in all sorts of new directions!

I'll never complain about excess information... thanks for the schematic!  Any chance you could explain the diode in parallel with the motor(s)?  I suppose I don't understand it because I really don't understand inductive loads either.  Please point me to a place to read up on this if it is too much to explain.

Also, electrons flow from s (source?) to d (drain?) in the MOSFET, but conceptually, I can think of current going from + to -, or drain -> source -> ground, right?  

I knew a simple project would still expose a bunch of stuff I didn't know!  With optoisolators (or a transistor) in place, can I drive the motors off of the +9V pin on the Arduino?  What about a capacitor across the wires to the fan?  My newbie-sense tells me this could smooth spin-up current demands.  

I wish I had a good beginner's set of components on hand, but I will start off playing with a couple transistors to drive the motors.  I'd need an NPN transistor, right?  Is there any reason current could flow back through it, requiring a diode somewhere?  (I'll read up on inductive loads this weekend).

Thanks... the adapter (on the 9V setting) puts out about 9.2 V.  This seems to stay constant with varying loads from the Arduino.  I'm assuming that the Arduino board can easily handle a few 80mA fans.

One last question... does it really matter what kind of wire I use to connect the fans?  I thought about using some spare Cat-5 Ethernet wire.  Too thin?  Is it better to use single-conductor (single-strand)?

I get paranoid about things I don't understand.  Hence the need to understand them...  

While I understand the basics, electricity still seems like magic to me.  (I'm a software guy).  I would like to use an Arduino to control some fans that cool my entertainment center cabinet.  However, I don't want my lack of knowledge to end up starting a fire.  

Feel free to ridicule me if I'm being needlessly paranoid, but here's my situation:

I have an AC/DC adapter soldered to a 2.1mm plug.  It is regulated, rated at 800 mA, and UL listed.  I'll use this to power the Arduino 24 hours a day.  Three 120mm case fans will be attached to the digital output pins.  The fans are rated at 80mA (@12V) and will be switched on or off (no need to PWM) based internal temperature of my cabinet.

What would happen if I accidentally caused a short to the power supply?  What level of safety does the UL listed mark imply?  Should I put in a fuse?  Buy insurance?    

Any other standard safety procedures for electronics projects?


Thanks!

There is more information about how to connect the LED here: http://www.arduino.cc/en/Tutorial/BlinkingLED  Basically you just put the long lead of the LED in pin13 and the shorter lead in the hole labeled GND.  The Arduino board will supply the power on pin 13.

For wiring things up easily, breadboards are essential.  Look here for info: http://en.wikipedia.org/wiki/Breadboard