In the last section we saw that the Rumble Robot controller transmits commands via infrared light. Each controller has an A setting and a B setting. When you switch between the settings, the microchip changes the flash pattern of the infrared signal.
The robot has A and B settings as well. When you switch the robot from A to B, it will ignore the A-pattern signals, but will register the B pattern signals. If you have two robots of the same model, you have to set one on B and one on A. Otherwise, one controller would activate both of them. Different models use different patterns, to make battling easier.
The central element of the infrared receiver is a small photocell, an electrical component that responds to light. Photocells are one widespread application of the photoelectric effect, the emission of electrons by certain materials in response to certain frequencies of light.
The typical photocell consists of a light-sensitive semiconductor layer, sandwiched between two electrodes. The battery sends a constant electrical current across the two electrodes, whether the photocell is exposed to light or not. When you expose the photocell to the right kind of light, the boost in electrons amplifies the current flowing across the electrons. If the light flashes on and off, the current will increase and decrease in the same pattern. In this way, a photocell translates the light signal into an electrical signal (see How Solar Cells Work for more on this process).
The electrical signal passes on to the robot's central integrated circuit. Based on the digital pattern of this signal, the integrated circuit carries out certain actions, such as moving forward, turning or throwing a punch. In the next section, we'll look at the components involved in these actions.