I have an Arduino Uno R3, a wave shield with SD card slot and speakers, a PIR sensor, and two 12v .38a PC fans. I need the sensor to sense motion then activate preloaded sounds from the SD card, and power the two fans simultaneously. What else do I need hardware wise for this to work. Is this even possible with one Arduino? My research indicates I need another a motor shield to power the fans but can that be stacked on top of the wave shield? I'm totally new at this so thanks in advance for any guidance!
You don't need a motor shield, you need a transistor or darlington transistor or "logic level" mosfet for the fans. See the picture for "Connect a DC motor" on this page, http://arduino.cc/forum/index.php/topic,154549.0.html
If you don't want to solder a driver, you can buy a motor driver. But the shields I know use a lot of pins and will conflict with the Wave Shield.
Can any of those options allow me to control the rpm of the fans? I need them to go full speed for the first few seconds then throttle back. Thanks!
arduinonewbee: Can any of those options allow me to control the rpm of the fans? I need them to go full speed for the first few seconds then throttle back. Thanks!
Yep, as the pic shows you can PWM the transistor... You'll need to code your way round going full speed for a while, perhaps with delay() but that's not processor efficient but it works, then set the slower speed.