User:Timpo/Sli-fi

Sli-fi is an acronym for Smartphone Light Interface for Flying instruments and is a means of transmitting information between a mobile telephone and a scientific instrument mounted on an airborne platform.

History
Radio-controlled aircraft allow a pilot on the ground to adjust the flight dynamics of an unmanned aerial vehicle with only four parameters which are thrust or power level, the Yaw or direction, the pitch or angle of attack and the roll or twisting movement. They are used as platforms for various instruments that can detector a wide spectrum of emissions from very low radio frequencies, to invisible infra-red (heat), visible light (cameras)right through to gamma rays. they may also be fitted wit tools such as cutting, catching and cleaning mechanisms.

The usual aircraft flight control system controller contains two joysticks: one for roll and pitch (as in a fixed wing aircraft style control column and the other operating the yaw (rudder) and thrust (throttle)

A smartphone has a touchscreen that both accepts input from finger position and also displays output. Usually these functions are visually connected, but are actually separate. the instrument is usually arranged to ignore more than one finger position, but with most technologies can process two or more signals, were the screen set to operate as two joystick controllers. A small dot or circle below the controlling fingers shows the current 'joysticks' position.

The bluetooth facility uses short-wavelength UHF radio waves in the ISM band from 2.4 to 2.485 GHz )can interact with the remote platform, but class 1 only has a range of about a meter and even class 3   (100mW) is limited to about 100 meters. Fortunately the flashlight facility on smartphones is a white Light-emitting diode that can be modulated with Li-Fi which is  a bidirectional, high speed and fully networked wireless communication technology similar to Wi-Fi. Coined by Prof. Harald Haas,

VLC, visible light communication is a subset of optical wireless communications technologies. the difficulty is that the torch has a rather narrow beam, which needs to be orientated and decollimated to be aligned with the camera. This can be done with a physical attachment to an unmodified standard smartphone, but is more conveniently done by cutting the case and moving both the light source and the camera to the middle part of the longer side of the touchscreen.

This allows the operator to see the robot on the screen and to preview the information it is gathering, as well as showing images of the environment from from one or more on-board cameras. The volume of information that a li-fi arrangement has a wide bandwidth and so can download in realtime a larger volume of data than most radio links. Difficulties arises when the vehicle experiences major or total occultation from the controlling smartphone by intervening obstructions, and for this reason a group of linked smartphone operators may have be deployed in visually cluttered sites.

As with regular flight training the transfer of control between operators depends on effective discipline.