Many TVs and other equipment are controlled by infrared remotes. When you point the remote at the TV and press the channel-up button, it changes the channel for you. Pressing the button makes the remote flash a pattern of infrared light at the TV. Infrared light is not visible to humans, but the TV’s infrared receiver detects the flashing light pattern. The TV’s microcontroller decodes this pattern and uses that information to change the channel for you.
The infrared light (IR LED) and receiver work great as "flashlights" and "eyes" for your ActivityBot. The IR LEDs shine forward, and the IR receivers detect reflections off of nearby obstacles.
The Propeller microcontroller receives reflection data from the IR receivers and uses it to make navigation decisions. In this way, your ActivityBot can roam around obstacles without first bumping into them.