A telecommand or telecontrol is a

command Command may refer to: Computing * Command (computing), a statement in a computer language * COMMAND.COM, the default operating system shell and command-line interpreter for DOS * Command key, a modifier key on Apple Macintosh computer keyboards * ...

sent to control a remote system or systems not directly connected (e.g. via wires) to the place from which the telecommand is sent. The word is derived from ''tele'' = remote (

Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...

), and ''command'' = to entrust/order (

Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through ...

). Systems that need remote measurement and reporting of information of interest to the system designer or operator require the counterpart of telecommand,

telemetry Telemetry is the in situ collection of measurements or other data at remote points and their automatic transmission to receiving equipment (telecommunication) for monitoring. The word is derived from the Greek roots ''tele'', "remote", an ...

. The ''telecommand'' can be done in real time or not depending on the circumstances (in space, delay may be of days), as was the case of Marsokhod.

Examples

*Control of a TV from the sofa *Remote guidance of weapons or missiles *Control of a satellite from a ground station *Flying a

radio-controlled airplane A radio-controlled aircraft (often called RC aircraft or RC plane) is a small flying machine that is controlled remotely by an operator on the ground using a hand-held radio transmitter. The transmitter continuously communicates with a receiver ...

Transmission of commands

For a Telecommand (TC) to be effective, it must be compiled into a pre-arranged format (which may follow a standard structure), modulated onto a carrier wave which is then transmitted with adequate power to the remote system. The remote system will then demodulate the digital signal from the carrier, decode the TC, and execute it. Transmission of the carrier wave can be by ultrasound, infra-red or other electromagnetic means.

Infrared

Infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of Light, visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from ...

light makes up the invisible section of the

electromagnetic spectrum The electromagnetic spectrum is the range of frequencies (the spectrum) of electromagnetic radiation and their respective wavelengths and photon energies. The electromagnetic spectrum covers electromagnetic waves with frequencies ranging fro ...

. This light, also classified as heat, transmits signals between the transmitter and receiver of the remote system. Telecommand systems usually include a physical remote, which contains four key parts: buttons,

integrated circuit An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or a microchip) is a set of electronic circuits on one small flat piece (or "chip") of semiconductor material, usually silicon. Large numbers of tiny ...

, button contacts, and a

light-emitting diode A light-emitting diode (LED) is a semiconductor Electronics, device that Light#Light sources, emits light when Electric current, current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy i ...

. When the buttons on a remote are pressed they touch and close their corresponding contacts below them within the remote. This completes the necessary circuit on the circuit board along with a change in

electrical resistance The electrical resistance of an object is a measure of its opposition to the flow of electric current. Its reciprocal quantity is , measuring the ease with which an electric current passes. Electrical resistance shares some conceptual parallel ...

, which is detected by the integrated circuit. Based on the change in electrical resistance, the integrated circuit distinguishes which button was pushed and sends a corresponding

binary code A binary code represents text, computer processor instructions, or any other data using a two-symbol system. The two-symbol system used is often "0" and "1" from the binary number system. The binary code assigns a pattern of binary digits, als ...

to the light-emitting diode (LED) usually located at the front of the remote. To transfer the information from the remote to the receiver, the LED turns the electrical signals into an invisible beam of infrared light that corresponds with the binary code and sends this light to the receiver. The receiver then detects the light signal via a

photodiode A photodiode is a light-sensitive semiconductor diode. It produces current when it absorbs photons. The package of a photodiode allows light (or infrared or ultraviolet radiation, or X-rays) to reach the sensitive part of the device. The packag ...

and it is transformed into an electrical signal for the command and is sent to the receiver’s integrated circuit/

microprocessor A microprocessor is a computer processor where the data processing logic and control is included on a single integrated circuit, or a small number of integrated circuits. The microprocessor contains the arithmetic, logic, and control circ ...

to process and complete the command. The strength of the transmitting LED can vary and determines the required positioning accuracy of the remote in relevance to the receiver. Infrared remotes have a maximum range of approximately 30 feet and require the remote control or transmitter and receiver to be within a

line of sight The line of sight, also known as visual axis or sightline (also sight line), is an imaginary line between a viewer/observer/ spectator's eye(s) and a subject of interest, or their relative direction. The subject may be any definable object taken ...

Ultrasonic

Ultrasonic is a technology used more frequently in the past for telecommand. Inventor

Robert Adler Robert Adler (December 4, 1913 – February 15, 2007) was an Austrian-American inventor who held numerous patents. He worked for Zenith Electronics, retiring as the company's Vice President and Director of Research. His work included developing ...

is known for inventing the

remote control In electronics, a remote control (also known as a remote or clicker) is an electronic device used to operate another device from a distance, usually wirelessly. In consumer electronics, a remote control can be used to operate devices such ...

which did not require batteries and used ultrasonic technology. There are four aluminum rods inside the transmitter that produce high frequency sounds when they are hit at one end. Each rod is a different length, which enables them to produce varying sound pitches, which control the receiving unit. This technology was widely used but had certain issues such as dogs being bothered by the high frequency sounds.

New applications

Often the smaller new remote controlled airplanes and helicopters are incorrectly advertised as radio controlled devices (see

Radio control Radio control (often abbreviated to RC) is the use of control signals transmitted by radio to remotely control a device. Examples of simple radio control systems are garage door openers and keyless entry systems for vehicles, in which a smal ...

) but they are either controlled via infra-red transmission or electromagnetically guided. Both of these systems are part of the telecommand area.

Encryption

To prevent unauthorised access to the remote system, TC

encryption In cryptography, encryption is the process of encoding information. This process converts the original representation of the information, known as plaintext, into an alternative form known as ciphertext. Ideally, only authorized parties can d ...

may be employed.

Secret sharing Secret sharing (also called secret splitting) refers to methods for distributing a secret among a group, in such a way that no individual holds any intelligible information about the secret, but when a sufficient number of individuals combine t ...

may be used.

References

{{Authority control Remote control