Switches Series Part 1: Types of Switches

-- by Liza MacLean, OT

Switches are necessary tools in our daily lives. Think about all the ways you interact with your environment to make things happen: you wake up in the morning and turn off your alarm clock and turn on the light; you flick the television on with the remote control to watch the news; when you get to work you turn on your computer and type some emails. How do you do all of this (and more) when you don’t have the range of motion, strength or dexterity to reach, grasp, press, push or manipulate all of those switches, buttons and keys?

The short answer is with a different kind of switch, commonly known in the AT world as a “single switch”. A simple definition of a standard switch is that it is an electromechanical device that is used to activate or deactivate an electrical signal by opening or closing a contact. An assistive technology single switch is a bit different in that it typically consists of a momentary contact switch, cord/cable and a 3.5 mm mono plug.

So how do single switches work? And what can you do with them?

Depressing or activating the momentary contact switch closes the electrical circuit and activates the equipment that the switch is connected to via the 3.5 mm plug. A single switch can be connected to a range of equipment or technology such as:

• A toy that has been specially adapted to be activated with a switch 
• A PowerLink environmental control unit to turn a radio or a lamp on/off
• A range of environmental control devices (infrared or radio frequency) to operate the TV, DVD, stereo, telephone and even the whole house (e.g. lights, doors) via home automation systems
• A computer (via a switch interface) to allow access to single switch games, or to access email, internet and type documents via an on screen keyboard
• A powered wheelchair to turn it on/off, change modes and even drive the wheelchair
• A range of speech generating devices to provide voice output for people with communication impairments. 

As you can see, these clever little devices help to adapt a huge range of equipment for individuals with disabilities to enable them to engage and participate in activities and have control over their environment that they might otherwise not be able to achieve. 

The big question many people ask is ...

When should you start using switches?

Previously it was thought that a child had to show an understanding of cause and effect before introducing switches, however current research and practice has shown that the use of switches can help to teach cause and effect to children with disabilities, so the earlier you can introduce switches into play and therapy sessions the better. For older children or adults, the choice to use a switch as an access method should be when their physical skills aren’t adequate to use other access methods (see my article on the access hierarchy) or when their cognitive skills mean that other access methods may be too complex, or a combination of both of these factors. 

How does a person with a disability access a switch? And what type of switch is best?

I’ll explain more about the principles and process of switch assessment in my next article, but in summary, switches come in varying shapes, sizes and have different activation methods. If there is a body part that can be independently controlled, then there is usually a switch that can be found to capture that movement.

Type of Switches

Switch types can be grouped into the following broad categories:

Mechanical switches – these are switches which are activated by physically depressing or grasping the switch with movement of a body part such as a hand/finger/head/foot/knee/elbow/eyebrow/cheek/tongue etc. Examples of these types of switches are the Jelly Bean Twist, Buddy Button, Moon Switch, Smoothie, Jelly Beamer, Big Beamer, Pillow Switch, Specs Switch, Grasp Switch etc. Mechanical switches are the most commonly used switches with many people with disabilities and have the advantage of providing auditory (sound/click) and tactile (the feel of depressing/activating the switch) feedback which is helpful for people just learning how to use a switch, and for those with visual and cognitive impairments. Wireless switches are available too.

Touch/low touch switches – these switches require less force to activate for people that have reduced strength but don’t offer the same auditory and tactile feedback as mechanical switches. Examples of these types of switches are the Plate Switch, Membrane Switch, etc

Sensor/proximity switches – these switches are activated by the slight movement of a body part such as a muscle twitch, or a movement to break a beam or to come within a certain range of a switch to activate it. They are useful for people with very limited strength and movement such as motor neurone disease. Examples of these switches are Eye Blink Sensor, Adjustable Proximity Sensor, Peizo Switch Candy Corn Switch, Mini Beamer etc.

Sip/puff switches – these switches can be activated with the mouth with either a single function of sip or puff, or dual function of both sip and puff (to control more than one device, or for two switch scanning). They are frequently used with people with limited upper limb movement, such as high level quadriplegia.

Voice/sound switches – these switches are activated by sound or voice and are useful for people with limited physical control, but can also be sensitive to other extraneous noise in the environment. 

In my next article, I’ll help you with the process of carrying out a switch assessment, and choosing the best switch, movement and switch position for the user.