It's speed is dependent on how much toward the 12 volt source the wiper is moved. 15 degrees of center. Any voltage applied outside this range will cause the motor controller input amplifiers to overdrive and to discontinue output and the motor will stop abruptly. The free end of one 2200 ohm resistor now goes to the PH terminal, the free end of the other 2200 ohm resistor now goes to the PL terminal and the center terminal of the potentiometer still goes to the PW terminal. If you get tired of diddling with a pot, or if your application requires it, this motor control board can also be controlled by a micro controller.
Internal safeguards prevent the controller from working without it.
A control voltage from a filtered PWM output of a micro controller such as the Basic Stamp, or PIC16F84 or any other of your choice can be utilized. It must be within the voltage constraints discussed previously and is applied to the PW terminal directly. See other pages of this site for examples of how to do this as well as downloadable sample programs. It is important to be sure that the ground from the microprocessor circuitry and the ground from the motor control circuit are tied together. For some strange reason, this is not covered under warranty.