2. Electronic switchesElectronic switches differ from mechanical switches in that they require a power source for operation and theneed to depress a switch is eliminated. No force or contact is required to activate, just motion across a field,beam or sensor. Some options to choose from are proximity, fibre optic and infrared switches.• Proximity switches require a body part to enter the field of the switch.The range or field and speed are adjustable. Proximity switches can beplaced in any position required. Some examples are near the jaw/chin,in a tray top or a head array. They will operate through most materials,depending upon thickness. www.asl-inc.com/Catalog/Index.asp?use=226• Fibre optic switches. Thin transparent fibres (plastic) emit an invisible beam of light (worksthrough internal reflection, ref: Wikipedia) that can be positioned to be broken by a body part forswitch activation. A fibre optic switch would be suitable to operate a single switch scanning system,which will be covered below. Common locations for a fibre optic switch could be the chin/jawarea and the tray top. An example of use: several holes would be cut into a tray top with beamsdirected up through each. The user would move a finger across the hole corresponding to thedirection of choice to move the wheelchair. Direction and speed are set, but programmable.• Infrared switches involve “…frequencies beyond the red end of the visible spectrum, i.e.frequencies with longer wavelengths than red light. Perceived by humans as heat. Commonlyused for remote-control devices…” (ref: Wikipedia).• An example of an infrared switch is the Self-Calibrating Auditory Tone Infrared (SCATIR) switch. It“…works by detecting a beam of reflected pulsed infrared light. The Switch is a momentarycontactoptical switch with auditory feedback. It is suitable for use with a variety of control gestures,such as eye-blink, eyebrow movement, finger movement, head movement, and facial musclemovement. It can be activated at a distance so the controlling body part does not need to be inphysical contact with the switch sensor.” www.spectronicsinoz.com/product/scatir-switch• Infrared switches are similar to the fibre optic switches in that they are most commonly used withsingle switch scanning systems. Both would be placed according to individual requirementsin similar places and require movement in or out of a field to activate. Speed and direction are set,but programmable.Non-proportional DevicesHead arrayThe ASL head array is one type of head array. It consists of a three-piece head supportwith a proximity switch embedded in each pad. The three switches provide forward, leftand right with some veer possible when activating two pads simultaneously. Reversecan be added to the system using a sequence of taps to change forward to reverse.Alternately, reverse can be added using a separate switch.www.asl-inc.com/Catalog/Index.asp?use=226
Scanning systemsScan systems allow the user to operate wheelchair and seat functions with a single switch.To operate the wheelchair, the user would watch the visual display unit located in front ofthem as a set of direction arrows light up in sequence. When the direction of choice is lit,the user would activate the switch to select. Pressure on the switch must be maintainedto continue moving, as momentary* (not latching*) switches are used for safety reasons.www.asl-inc.com/Catalog/Indexd978.html?use=226The location and type of switch is chosen to best suit individual function. The switch canbe mechanical or electronic. Scan systems are available through ASL, Penny & Giles andDynamic. Current technology can incorporate a scan system into the master control unitof the wheelchair, e.g. G91s by Dynamic, as pictured.www.dynamiccontrols.com/index.cfm/1,92,htmlScan systems can be cumbersome to use and, therefore, are mostly used when an individual has only onereliable switch site available and good scanning skills.The ClicktoGo is an example of a scanning device for switch operation of multiple systems.“The ClickToGo is operated by single or multiple switches via a scanning interface. Theeight direction indicators are illuminated by ultra-bright LEDs and can be scanned in manydifferent ways. When a direction is chosen, pressing a switch drives the chair.”• Integrating Communication, Environmental Control and Computer Access by UniquePerspectives Ltd” www.spectronicsinoz.com/browse.asp?cat=16969Heavy Duty JoystickThe heavy duty joystick is an example of a multi switch unit. The website states, “It haseight driving directions allowing selection of forward, reverse, left, right and the four diagonaldirections. Although a switched device, the Heavy Duty Joystick gives good performancewhen used with the correct acceleration and deceleration settings”.www.dynamiccontrols.com/index.cfm/1,92,htmlAs the name implies, the Heavy Duty joystick is an alternative for users who are hard on their joysticks andmay otherwise damage the electronics inside a standard proportional joystick.Sip and PuffSip and puff is pneumatic (mechanical) switch control. It is operated by intra oral air pressure, not respiration(Lange, 2005) and so can be used whilst using a ventilator. Four commands are used: hard puff, soft puff,hard sip, soft sip. The forward command is latched such that the wheelchair continues moving until a furthercommand is received to stop or change direction. An emergency stop switch is built-in to stop the systemshould the mouth piece fall out of the user’s mouth. A fibre optic switch can be used.Some versions have full directional control through the pneumatic switch commands. Others such as the ASLsip and puff system have a combination of intra oral control and head steering/veering. Further mechanicalor electronic switches can be added to increase options as needed.