Stepper speed control Sparkfun stepper pro

unlike the big easy driver. (which has a pulse pin), this board looks to speed controlled entirely in software by adjusting either the timing (delay) between "step" commands, or by varying the number of steps in thecommand for a fixed time. you could make either, (or both) the delay or number of steps a variable. you could adjust the variables in software, or use a physical input like a potentiometer or rotary encoder to change values. bear in mind most steppers develop maximum torque at a certain speed, so in practice thier speed is usually kept fairly constant and thier main purpose is usually precise positioning and holding position rather than speed control. having said that, I have successfully used the simpler "easy driver" board setting the speed (pulse interval) using Arduino's "tone" function as well as using other pulse sources like 555 timer ICs. if speed control is your main aim, perhaps also experiment with one of the "easy driver" type boards.