Bring to Light
Most remote control toys are operated by a radio transmitter. When you move the controls, the transmitter sends a radio signal, at a particular frequency, to a radio receiver inside the toy. The radio signal includes a distinctive set of electromagnetic pulses, which represents a particular command. The toy recognizes this command and carries it out. (See How Radio Controlled Toys Work for details.)
Rumble Robots operate on a similar system, but they use infrared light instead of radio waves. An infrared remote control is like a miniature Morse code lamp. It transmits messages by flashing a small light-emitting diode (LED) in a distinctive pattern of long flashes and short flashes. The infrared light emitted by the LED is invisible to our eyes, but not to the robot's light-sensitive panel. The sensor picks up the signal and deciphers the message.
This is the same principle used in standard television remote controls. In fact, the Rumble Robot controller looks a lot like a TV remote on the inside. The plastic controller housing contains:
- Three batteries
- A light-emitting diode
- Two circuit boards
Rumble Robots (as well as most other modern electronics) use printed circuit boards. A printed circuit board is a thin piece of fiberglass with thin copper "wires" etched onto its surface. These wires connect a number of electrical components together in a complex circuit.
The circuit boards in a Rumble Robot controller include:
When you move the plastic pads on the controller, they push down on the circuit board's buttons. The buttons are just pieces of rubber that hold small conductive plates. Pressing the button pushes the conductive metal piece up against a contact point on the circuit board. Normally, each contact point is an open section of the circuit between the battery and the integrated circuit. In other words, the etched wires do not connect, so the electric current cannot flow to the microchip. Pressing the conductive plate down on the wires closes the circuit -- the current flows across the plate from one wire to the next, and moves on to the microchip.
The integrated circuit sorts out which buttons are depressed, generates an appropriate command signal and passes it onto a transistor. The transistor amplifies the signal and activates the infrared light. The controller will keep sending the signal as long as buttons are depressed.
In the next section, we'll see what happens when this signal reaches the robot's light sensor.