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Access to the computer: switches, touchscreens, overlay boards, keyboard, mice

Common switch types:


1. Contact switches
These are the most common switches in school.
The user has to physically press or apply pressure to the switch to operate. Two state: on/off.
Most simply complete a circuit to make electrical contact, they do not need independent power source.
Most contact switches give tactile feedback (click and travel)
variables:
size/shape/colour- physical dimensions and characteristics of the switch surface
pressure -needed to operate the switch
travel -how much movement in the switch operation
feedback- tactile feedback (movement) and auditory click.
The switches usually terminate in a jack plug (either 1/4 inch or 3.5mm) (transfer between different sized jackplugs is easy)

Touch switches measure the change in inductance/capacitance in the switch surface (usually a metal plate). When touched by a hand/finger they trigger electrical contact. They need an electronic interface to record the switching. They are usually metal plates, they require contact with a surface that changes their capacitance (ie bare skin and it must not be too dry). The switches can be very sensitive to skin but most do not have any variable sensitivity control
Touch switches do not give any tactile or auditory response (unless addedwith additional hardware).

2. Non contact switches
These switches can detect movement or proximity to the switch surface.
Proximity switches need a power supply to operate, they do not give feedback unless they have additional electronics (auditory/visual).
Mercury tilt switches operate positionally by only making the contact (switching) when they are in a certain position.
Sound switches operate by switching in response to sound.
Peizo electric switches detects small muscle movements which trigger the switch operation.
Eye blink switches operate by changes in reflected light from the eye.
Light switches operate by switching in response to variations in light levels.
Suck puff switches operate in response to changes in pressure.

3. proportional switches
These switches can not only detect on/off state but can also measure The amount of movement.
The time the switch is pressed
and the pressure the switch experiences.

They can react variably to different levels of physical input.
The most common is the proportional joystick which reacts differently to movement.
Pressure sensing switches can operate differently in response to differing pressure.
Timed response switches can operate differently in response to the time the switch is pressed
(timed response switching can be simulated through the computer measuring the switch hold time and responding accordingly)
Proportional switches need a control device which can respond differently to different levels of input (e.g. electric motors, midi devices)

Soundbeam is a device which measures physical movement through utrasonics and converts that information into voltages which can operate a midi device.

Variable switch devices are not often used yet give the user much more flexibility in switch control. They allow the user to improve his or her physical switch operation.
They allow multiple switch activation without recourse to scanning especially useful for those individuals who find switch scanning difficult.

Switches can be operated by any movement (hand/finger/head/foot/elbow etc) For successful switch operation the movement must be easily repeatable and not involve too much physical effort or strain. There must be a good rest position and the switch must look acceptable for the individual.
The mounting of switches is important (positioned on table/mounted horizontally or vertically/ in plinth/built into head rest etc)

Overlay boards


The Overlay boards plug into the computer and is used to operate it in place of the keyboard.
The overlay board surface consists of a number of touch sensitive keys. Individual keys or groups of keys may be programmed to:
Paper or plastic overalys are placed on top of the overlayboard to show the user which keys and areas have been programmed onto the overlay board
two overlay boards are used in school: The concept keyboard and the intellikeys keyboard.

The concept keyboard


Plugs into the serial port at the back of the computer. It has to have special driver software to operate: Concept Plus Multimedia although some software (eg. Writing with Symbols) has the concept keyboard driver built in.

The Intellikeys board

Plugs into the keyboard connector of the computer so it can operate as an alternative letter board without additional software. It gives complete control over the computer, mouse and menus. It comes with a number of overlays which it recognises automatically. It also has two switch jack sockets for switch use so it can be used as a programmable switch interface.
The Intellikeys can be programmed with OverlayMaker and uses Intellipics as a multimedia authoring program.

Switches - Choosing a Movement

Switches can be operated in different ways; hands, head, foot etc. The switch may need a special mounting system to allow the desired method to be used.

Repeatability - A switch user will have to make a large number of switch presses which may take considerable effort.

Outcome - Make sure that the result of their efforts is worthwhile. Remember that there may be easier ways of doing something rather than struggling to use a switch.

Acceptability - The user's choice is final.

Access to other activities - The switch position should not obscure the task to be operated and should not get in the way of daily activities. The user should be able to work the switch and see the activity easily - remember that it can take some time for them to transfer their attention from the switch to the task. If this takes too long they may miss the activity.

Ease of use and setting up - A good switch system should be chosen; one that takes a minimum amount of time and effort to set up, and does not require a degree in engineering.