I'm certainly a rookie when it comes to electronics. I've seen several examples of Arduino driving DC motors, all of which require diodes since DC motors are inductive loads.
I've torn apart a few old broken devices at my home (a VCR, a Cassette player) and scavenged the motors from them. For the most part, the motors require 12V to run. I know that Arduino is only capable of outputting 5V (not to mention too low an amperage to power these motors). So, I've got a couple of old DC adapters that I've also picked up to drive these motors in my projects.
I guess I have two questions:
First, all of the DC motor projects that I've seen use a common ground. Does this mean that I'll have to connect the negative lead from the DC adapter to the ground pin of the Arduino when I drive these motors? Also, couldn't a transistor eliminate the need for diodes? If I send 5V to the base, and let the collector/emitter send the 12V through the motor, wouldn't I have covered my butt?
Second, what type of diodes should I use? My local Radio Shack has rectifier and zenier (sp?) types. What's the difference and what would make one choice better than the other?
If you have 2 power supplies, yes... you connect the ground potential of each together to create common ground. It's required to have your circuit "behave" correctly.
Also, couldn't a transistor eliminate the need for diodes?
I'm afraid you lost me here. If you will be driving a 12V MOTOR from the Arduino a diode is of little use. You will NEED a transistor. And you will need the transistor to behave, so driving the base with 5V and no current limiting resistor will "stress" things a bit. Put at least a 1K OHM resistor between the Arduino Pin and the NPN base.
Rectifiers are for controlling direction of flow. Zeners are for voltage regulation circuits. Zeners do not make good alternatives to rectifiers since they are designed to break down and allow reverse flow above a set threshold... AKA they will behave to be a bad rectifier... That "threshold" is their "regulation voltage" that you see on the package at radio shack. Check out a Zener circuit... you will see them in "backwards" for a reason.