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Introduction The Self-Calibrating Auditory Tone Infrared (SCATIR) Switch is an experimental multipurpose momentary-contact optical switch with auditory feedback designed for use by persons who experience difficulty in activating mechanical switches. It works by detecting a beam of reflected pulsed infrared light. It is suitable for use with a variety of control gestures, including eye-blink, eyebrow movement, finger movement, head movement, and facial muscle movement. Because it works on an optical principal, it can be activated at a distance. The controlling body part therefore need not be in physical contact with the switch sensor. Dimensions are 2.5cm x 6cm x 9.5cm.
Theory The SCATIR Switch makes use of a sensor consisting of an infra-red-sensitive phototransistor. These two electro-optical devices are positioned so that they share virtually the same optical axis. This becomes the optical axis of the sensor. The switch is activated whenever an infrared-reflective surface (such as skin or light clothing) is placed on this optical axis at a distance within the range of the switch.
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Adjustment of the Activation Distance
The maximal distance allowed for the activation ("activation
distance") can be adjusted from a few centimeters to less
than a millimeter. This adjustment can be made manually or
automatically
(self-calibration), as explained below. When the activation distance
is reduced to its minimal value, the switch simulates a zero-force
touch switch. When an activation distance of, say, three centimeters,
is chosen, the switch can be activated from as far away as three
centimeters. This permits more cosmetically appropriate switch
placement, such as in or on a wheelchair headrest. It also frees
the user from the physical constraint of actually having to touch
the sensor surface. The switch can be activated through a transparent
protective or supportive structure, such as a clear plastic lap
tray.
Auditory Tone The switch incorporates an auditory tone source which emits a high- frequency beep when the switch is activated. This auditory feedback can be enabled or disabled by means of an internal selector switch. The user can select either of two auditory feedback modes: Discrete beep mode: a short momentary beep to indicate activation, which returns to silence regardless of the length of time the switch remains activated. Continuous Tone Mode: a tone which lasts as long as the switch is activated.
Output Relay The SCATIR switch provides access to an internal relay through a standard 3.5mm phone jack. This provides a switch closure suitable for small- current devices. DO NOT use this output for direct control of line-powered (120 volt) devices. For such purposes, an additional external relay must be used to isolated the SCATIR switch.
Self-Calibrating Mode When
the switch is to be activated by a body part that cannot always
maintain a constant activation distance from the sensor, the switch
can be operated in self-calibrating mode. In this mode, placing
the activating body at ANY given distance within the range of
the switch will serve to define that distance as the activation
distance. Once activated at this distance, the switch may be turned
off by moving the body part completely out of the optical axis
of the sensor.
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Manual Calibration Mode When in manual
calibration mode, the activation distance is set by the user by
adjusting a potentiometer (variable resistor). Once the distance
has been set, it will remain the same until readjusted. To set
the distance, place the activating body part just slightly beyond
the desired activation distance and turn the potentiometer until
the tone stops. The manual calibration mode is especially useful
if the path traced by the activating body part is along the optical
axis of (directly in line with) the sensor.
DIP Switch Settings [See Figure 1] Inside the battery cover of the SCATIR switch is a four-station DIP switch. The first station turns on or off the auditory tone feedback. The second station changes the tone mode (beep or continuous). The third and fourth stations determine the calibration mode (self-calibrating or manually adjustable).
Figure 1: Copy of instructions on inside of
battery cover
Power Source /Recharging
The SCATIR switch is equipped with
a new Nickel Metal Hydride (Ni/MH) rechargeable battery. This
battery does not develop a memory effect as did its predecessor,
a nickel cadmium(NiCad) battery. Occasional deep cycles (total
discharging and full recharging) are not needed. The capacity
(amount of charge) that the battery is capable of holding is also
higher than the nickel cadmium battery. However please observe
the following charging instructions to avoid overcharging the
battery and shortening its usable life.
To recharge the Nickel Metal Hydride (Ni/MH) battery in the SCATIR
switch, insert the cylindrical plug of the charger into the charger
jack labeled "12 v in" on the side of the SCATIR
switch. The yellow LED near the charger jack lights up to indicate
that the charging current is going to the battery. The charging
time for a fully discharged battery is 14 to 16 hours with the
SCATIR switch turned off. Charging with the SCATIR switch on requires
about 48 hours. The charger may be left plugged in continuously
without harm to the rechargeable Ni/MH battery only if the SCATIR
switch is left turned on and the sensor is plugged in. Charging
the Ni/MH battery for several days with the SCATIR switch turned
off will shorten the life of the battery. Do not attempt to
charge non-rechargeable batteries. Do not plug the charger into
the SCATIR Switch if a non-rechargeable battery is installed.
[Note: The charging circuit of
the SCATIR switch has been designed to facilitate replacement
of the charger, if necessary. The charger that comes with the
SCATIR switch may be replaced by any 12-volt unregulated (16-24
volts open circuit) power supply with a coaxial plug that is 5.5
mm outside diameter and with a 2.1 mm inside diameter. The output
of the charger may be either polarity DC, or even AC. Radio Shack
adapters 273-1652 or 273-1610 may be used. Power may also be obtained
from the battery of a powered wheelchair. For details on how to
use a wheelchair battery for powering the SCATIR switch, contact
the Artificial Language Laboratory.
A suitable replacement battery
is available at Radio Shack: 9V/150mAh Rechargeable Ni-MH Battery, Radio
Shack Catalog #: 23-529]
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