Assistive Technology - Tools and Applications 6

Switches and Scanning

Air Link infra-red switch

Jelly Bean switch

In AT terms, a switch usually refers to an object that can be touched or activated by a body part in order to give commands to a computer by a person with restricted motor control.

With related software, a single body movement can operate a computer via a switch.

This requires a training and learning period, and pupils' expectations should not be raised too much as it is very slow in operation.

A switch makes an electrical connection between two contacts, such as a light switch. The button on a mouse and a key on a keyboard are switches. In AT terms, a switch usually refers to an object that can be touched or activated by a body part, in order to give computer commands. This usually refers to touch, but puff (blow) and suck switches are other examples.

Switches are, therefore, useful to pupils who are limited to gross motor movement and can only touch a single, fixed target. They are also useful to those with very fine, but limited, motor movement, such as those restricted to head control. With the use of appropriate software, input by switch can manipulate a computer.

Most switches are contact switches - they operate by touch or grip, and give feedback, such as a click, or spring return. This audio and tactile response is important for users who cannot easily tell what their limbs are doing.

With momentary switches, such as a key on a keyboard, the switch remains on until you release it.

For pupils who cannot speak, switches such as the BigMac will play a pre-recorded message. Switches are also available to operate toys.

Multiple switches are also available, where a variety of functions need to be performed by different switches. The Wafer Switch is an example. These do not give audio or tactile responses.

Selection and positioning of switches

There are a large variety of switches available and selection will depend on the user's needs. A large switch, screwed to a table, may be necessary for a pupil with gross and un-coordinated hand movement. On the other hand, a soft head-switch, attached to a wheelchair with Velcro, might be an option for someone that can control head movement.

Positioning of the switch to achieve comfort, control and consistency will need trial and error, and perhaps a little ingenuity. It should be as accessible as possible for the user, and need the minimum of intervention to allow him or her to use it.

Software programmes are available to help motivate and train switch users. These are sometimes in game form, with simple cause and effect being the most basic. Inclusive Technology's SwitchIt suite is an example.

Software for switches

In order for a switch to work, the user must have some method of choosing an action to activate by pressing the switch. This is normally achieved by scanning software. This is different from the scanning used in 'electronic copying' and involves a method of selecting a target option on a computer monitor. This is normally achieved by selecting the desired action from a range of options automatically displayed on the monitor, usually presented on a moving row or grid basis. A single switch can, therefore, be used to operate a normal computer. Much of the software designed for special needs, such as Clicker, will have a scanning option.

Scanning is actually relatively easy in operation, but does require a training period. However, pupils' expectations of switch use should not be raised too much as it is very slow. Teachers might try writing a paragraph, using a switch, to gauge its limitations. Nevertheless, for some pupils it may be the only means of access.