1. Contact switches
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 added).
2. Non contact switches
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.
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)