Abstract from Fall 2013 MidTerm Paper

Introduction
This paper covers the theory and practical use of a controller powered by an Atmel micro controller to operate a boost converter power driver used in an electric bike configuration.
A typical electric bike setup has a single voltage source to drive the motor from a controller. This presents a limitation because the battery size will dictate how fast and far the electric bike can travel. With a fixed voltage, the battery size must be specified. Smaller batteries are lighter, charge quickly, cost less, and are easier to service. However, they are limited in speed and distance. Larger batteries can operate and greater speeds and travel further distances, but are heavy, expensive, and take longer to charge.
Use of a boost converter is one option to get the benefit of small and large battery setups. The boost converter takes the voltage from the small battery and “boosts” it to a higher value, which is used to drive the motor at higher speeds. The converter is not 100 percent efficient, so some energy is used, somewhere in the range of 5-15% loss. This loss generates heat, so the boost converters are fitted with a heat sink to dissipate it from the device.
This project fills in the gaps by adding an output level controller that is operated from a switch mounted on the handlebars of the bicycle. When the operator presses the switch, the voltage boost is active. Another press of the switch returns the bicycle to the default voltage level of the battery. This is all done by means of an Atmel ATTiny85 microcontroller.

The entire paper can be read here