Page 171 - Handbook of Electronic Assistive Technology

Chapter 6 • Environmental Control 159

of 3 s, but adjustable and set within the SPIU itself to avoid reliance on the transmitted
control signal for this safety-critical timing. Connection to the bed or chair motor set is
achieved using a ‘Y’-branched lead or a multiple port module. This allows the standard
handset also to be connected and provide full control. Typically, only some functions are
enabled for EC.
The SPIU is operated by the EC controller in response to a corresponding user selec-
tion. This control in early-generation ECS was by direct cable connection and progressed
to remote signal control, either IR or RF with second-generation systems. IR is used for
appliances within the single room, including the bed and chair control with a continu-
ous transmission signal. However, RF is typically used for call alarm functions (e.g., pager,
nurse call and community alarm) to ensure it can be activated from multiple rooms or
locations within the transmission range.
Lighting control provides an illustration of the evolution of control techniques with
the development of technologies. With first-generation systems, lighting control was
achieved using the peripheral interface units to directly switch the mains current sup-
plying the overhead light, initially under direct cable connection from the EC control-
ler and then using the remote RF relay units, which were often positioned in the ceiling
or loft void. With the introduction of commercially available IR-controlled wall panel
light switches, the same control could be achieved by fitting these as replacement light
switches and with IR signal control directly from the EC controller. The next development
was IR-controlled light bulbs, so that the adaptation for EC is reduced still further. For
extensive home lighting control there are also integrated systems incorporating all house
lights with interfaces for control from IR, WiFi and other sources. With home automation,
lighting and other functions have become a mass market product, from which EC users
can also benefit.

MOUNTING AND STANDS FOR EC CONTROLLER AND ACCESSORIES
The positioning of some components of the ECS can be crucial to its operation in some
applications (Fig. 6-5). For instance, the access method (e.g., switch) for the user to be
4
able to operate it and the EC controller for the display to be visible to the user. To satisfy
such requirements, various mounting systems and stands have been developed, including
attachments to wheelchairs, free standing from the floor or on a table top.

Controller Mode of Operation of Selection Process
Single Switch Scanning Access
Historically, the majority of EC controllers are ‘single switch scanning access’. The input
means has only binary states, on or off, representing whether the input device has been
activated or is not activated. In the majority of access devices this is actually an electrical
microswitch incorporated into a casing of a variety of sizes, shapes or a bespoke assembly.
It is therefore commonly referred to as a ‘user switch’. By selective voluntary movement,

4 http://possum.co.uk/.