Page 172 - Handbook of Electronic Assistive Technology

160 HANDBOOK OF ELECTRONIC ASSISTIVE TECHNOLOGY

FIGURE 6-5 Illustration of mountings and stands for environmental control equipment�
the user depresses the active surface of the switch and this is their means of selection. By
similar means, pneumatic pressure is translated to on/off electrical control for the EC,
with the sip/puff switch operated by user respiration or an air-filled pressure pad switch.
With only a single degree of freedom (two states), the user is only able to operate one
function directly for on/off control. However, by deploying a menu of control functions
which is scanned automatically, the two-switch state can be used to start the scan and
then stop it at the desired or selected function. The signal transmission to select the item
may then be sent immediately on stopping the scan, or require a subsequent user switch
press. Hence one of the tasks of the EC controller is the implementation of this process
and a logic algorithm for the selection mode of operation. In the first generation of EC
units this was achieved in solid-state logic, whereas later generations have embodied
software algorithms.
Associated with the single-switch scanning process are a number of configuration set-
tings, which allow optimisation to the individual and their abilities. This includes:
• Scan rate – the number of scans in a set period (e.g., per minute).
• Scan dwell time – time duration that the scan remains on each item awaiting selection.
• Input delay time – time from when the switch is activated until the controller registers it.
• Minimum switch activation time – time the switch has to be activated to trigger selection.
• Start scan delay time – time period after initial switch press that autoscan will commence.
• Repeat scan number – how many times each menu is scanned once started.