You should not drive high current or really noisy devices directly from the Arduino because it will destroy the CPU (the digital outputs are actually coming straight from the CPU itself). Examples: LEDs, traditional light bulbs, motors (steppers are exceptionally noisy), electromagnets, etc.

The solution is to use a “driver” circuit that takes power directly from your power source (bypassing the Arduino circuits), and using the Arduino digital outputs, drives the device. In your case you need a stepper motor driver (unless there’s already one built onto your stepper) – something like this should work: http://www.sparkfun.com/products/10267. I haven’t used steppers (I’m a newb as well), but it looks like the input for this driver uses Pulse Width Modulation (PWM), which means the digital signal is pulsing between high (probably +5VDC) and low (much lower, maybe +1VDC) a variable rate, and by adjusting this rate, you adjust the position of the stepper motor. A seemingly complete example is here: http://bildr.org/2011/06/easydriver/.

The rotary encoder can certainly be salvaged from an existing device, like a mouse – buy you’ll need to figure out the right voltage and stuff for it by hand (unless you can plug it in to your computer and test it). If you have to test it by hand, you should take it apart and see if you can touch the IR LED. Since it’s IR you can’t really tell if it’s on (unless you have a nightvision mode video camera or something). If you can see visible light coming from it, of if it’s generating any heat, turn it off immediately – there’s too much power. Either the voltage is too high or you need a current-limiter (low Ohm resistor) to keep the LED from pulling too much current.

Anyway, feel free to give me a shout if you need a hand figuring it out.

Thanks,

Steve

I’m loving your blog!

I am a complete Electronics Newb, but I have always been fascinated. I have a little home project on the go at the moment and basically need to control a stepper motor with a rotary encoder. Something like your mouse scroll wheel would be perfect. I want to be able to mirror the revolutions of the encoder on the motor i.e. 1 turn of the encoder = 1 turn of the motor (it is going to remotly control a swivelling platform).

In order to make the prototype I am trying to acquire the components that I will need. I have ordered an Arduino Uno and breadboard, some resistors and a stepper motor – I was hoping to use an old microsoft mouse like in your example.

Is there anything I am missing?

Sorry for such a helpless message!

thanks in advance,

Craig.

based on your pot check. For a 7-segment LED display like I’m using, you’ll need a serial to parallel LED driver since there are more LEDs than output pins on the Arduino, then you can get an Arduino driver and send it commands similar to that of the LCD display. I buy almost everything from SparkFun Electronics because they have a wealth of information about every product (here’s a serial LED Driver, for example: http://www.sparkfun.com/products/9622).

Thanks a bunch!

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