A scanner powered by the limited power available on a peripheral bus. In particular, the scanner can operate within the 2.2 watts provided over a USB connector. The scanner of the present invention uses a contact image sensor (CIS) which uses optics to distribute light from each light emitter to multiple pixel positions, preferably using a single LED for each color. An electric motor for driving the platen uses rare earth magnets to limit the power required. Instead of the traditional method of biasing the CIS scanner against the platen with a spring, the platen itself is spring-biased. The moveable spring biasing of a platen is possible because a worm drive motor is used allowing a helical thread on the worm drive to contact the platen gears as they move up and down as biased. Preferably, the helical thread of the worm gear has a single point of contact with a gear on the platen, further limiting the friction and allowing the platen to move up and down with respect to the stationary motor. Varied duty cycle digital pulses are used directly to drive the motor. Only the most significant bits are used to limit the amount of circuitry needed to calculate the speed. The digital controller circuit also operates on a 3.3 volt power supply. The platen itself is preferably made of a hard material to limit the footprint of the platen, and a small diameter platen is used.