The Cerebellum provides the user with two LEDs and two buttons that can be used to debug, enter information such as a start command, or just blink happily. The green LED is mapped to PIC16F877 pin B0, the yellow LED is mapped to B2, Button A is mapped to B4, and Button B is mapped to B5. These ports are also pinned out to the digital I/O bus; reference the digital I/O section for more information on using these signals as digital I/O.

Button A and Button B are both pulled low with a 22 kOhm resistor, and will connect to logic high when pressed - therefore the buttons are active high. A logical "high" or 1 will turn on the LEDs.

The red power LED is not under user control, but can still provide useful feedback. The power LED will blink if the Cerebellum detects a low battery condition. Under normal operating conditions, the power LED is continuously on.