Radio control (often abbreviated to R/C or simply RC) is the use of radio signals to remotely control a device. The term is used frequently to refer to the control of model vehicles from a hand-held radio transmitter. Industrial, military, and scientific research organizations make [traffic] use of radio-controlled vehicles as well. A remote control vehicle is defined as any mobile device that is controlled by a means that does not restrict its motion with an origin external to the device. This is often a radio control device, cable between control and vehicle, or an infrared controller. A remote control vehicle (Also called as RCV) differs from a robot in that the RCV is always controlled by a human and takes no positive action autonomously.
Dual-Tone Multi-Frequency (DTMF)
Dual-tone multi-frequency (DTMF) signaling is used for telecommunication signaling over analog telephone lines in the voice-frequency band between telephone handsets and other communications devices and the switching center. The version of DTMF used for telephone tone dialing is known by the trademarked term Touch-Tone (canceled March 13, 1984), and is standardized by ITU-T Recommendation Q.23. It is also known in the UK as MF4. Other multi-frequency systems are used for signaling internal to the telephone network. A DTMF TELEPHONE KEYPAD :
The contemporary keypad is laid out in a 3×4 grid, although the original DTMF keypad had an additional column for four now-defunct menu selector keys. When used to dial a telephone number, pressing a single key will produce a pitch consisting of two simultaneous pure tone sinusoidal frequencies. The row in which the key appears determines the low frequency, and the column determines the high frequency. For example, pressing the '1' key will result in a sound composed of both a 697 and a 1209 hertz (Hz) tone. The original keypads had levers inside, so each button activated two contacts. The multiple tones are the...