So many replies I think you might have a problem focusing on any given solution. Why don't you just put off the mosfet for the moment, in that unless you have or willing to obtain a logic level mosfetyou will just be making your project more complex then it needs to be to just run your motor.
Here is the classic drawing from the Arduino playground that can be used with solenoids or motorsup to 4 amp loads using a common TIP120 NPN power transistor:http://arduino.cc/playground/uploads/Learning/solenoid_driver.pdfYou would just wire your motor as a replacement of the solenoid L1 in the drawing.I would use the 1k ohm base series resistor. Note that you can either turn the motor on and offusing digitalWrite() commands, or you can run the motor at variable speeds from 0-100% usinganalogWrite() commands. Same circuit supports both modes of operation, you just have to pick an output pin number that supports pwm commands if you wish that option.
Do you think I implement the soft start here?
If you are using the mosfet in a switching mode, on or off only, then you need a gate voltage that fully saturates the device on, 10vdc for your device. That of course can not be provided by directly from an Arduino output pin. You can however wire up a normal npn transistor as a switching device ...
Or does this particular MOSFET fully saturate at 5v? How do I work that out from datasheet? I admit my eyes glaze over looking at all that detail. Which is the relevant parameter?I assumed that Sparkfun wouldn't release a product with a major design flaw, so is there something here I am missing? Will this shield work properly, or is there more to this than meets the eye?
Also figure 7 in the data sheet shows a graph of five different gate/source voltages curves (labled Vgs) and how much current each of those values will allow to flow from source to drain. This device will switch on and off just fine with direct connection to arduino output pins.
By the way SF seems to have that same switch board available in a single channel option ...
Oh yeah, I made one of those too. I know a little knowledge is a dangerous thing, so I wanted to make sure I had some small grasp on the fundamentals before wiring them up to something big.
That is much easier to implement in software. Just use analogWrite() statements starting with a zero value and gradually increase the PWM value to 255 (100% on) at whatever ramp-up speed you wish. Again be sure to wire to an output pin that supports PWM commands.