See PLL for schematics and source code. Power Bugdozer uses two 9-volt batteries, for a maximum of 18 volts. Rechargeable batteries are cheaper per use and landfill friendlier. The batteries are center tapped for the motherboard. So, only half the voltage is passed to the regulator, wasting less power.
Full voltage is provided to the LEDs and DC motors.
The Maxim MAX603 is at the heart of the onboard power supply. It can continue providing 5 volts even when the source drops to only 5.32 volts. Low current use. Unlike the National Semiconductor LM2940T used by Boe-Bot , this regulator sips very little current. All chips have 0.15-microfarad decoupling capacitors.