RC toys typically have a small handheld device that includes some type of controls and the radio transmitter. The transmitter sends a signal over a frequency to the receiver in the toy. The transmitter has a power source, usually a 9-volt battery, that provides the power for the controls and transmission of the signal. The key difference between radio controlled and remote controlled toys is that remote controlled toys have a wire connecting the controller and the toy, while radio control is always wireless.
Most RC toys
operate at either 27 MHz or 49 MHz. This pair of frequencies has been allocated by the FCC for basic consumer items, such as garage door openers, walkie-talkies and RC toys. Advanced RC models, such as the more sophisticated RC airplanes, use 72-MHz or 75-MHz frequencies.
Let's take a closer look at the RC truck we saw on the last page. We will assume that the exact frequency used is 27.9 MHz. Here's the sequence of events that take place when you use the RC transmitter:
1.You press a trigger to make the truck go forward.
2.The trigger causes a pair of electrical contacts to touch, completing a circuit connected to a specific pin of an integrated circuit (IC).
3.The completed circuit causes the transmitter to transmit a set sequence of electrical pulses (see How Radio Works for details). Each sequence contains a short group of synchronization pulses, followed by the pulse sequence. For our truck, the synchronization segment -- which alerts the receiver to incoming information -- is four pulses that are 2.1 milliseconds (thousandths of a second) long, with 700-microsecond (millionths of a second) intervals. The pulse segment, which tells the antenna what the new information is, uses 700-microsecond pulses with 700-microsecond intervals.