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The SCATIR Switch

Note: A new version of the SCATIR Switch is available from Tash, Inc.
The SCATIR Switch is no longer available for purchase from the Artificial Language Laboratory.
The information on this page is given for the benefit of users of the previous model of the SCATIR Switch.


Purchasing Information

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.

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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.

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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).

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Copy of instructions on instide of battery cover

Figure 1: Copy of instructions on inside of battery cover

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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.

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[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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This page was last updated March 30, 2005