Portable Stimulation and Assessment Tool

Designers: Kit Yee Au-Yeung, Daniel T. McCormick
Client Coordinators: Mary Caldwell
Supervising Professor: Dr. Larry N. Bohs

A portable sensory stimulation and assessment device was designed to aid therapists in evaluation of patients recovering from head injury and coma. Currently available devices are all very large or separately stimulating devices, often occupying an entire room. The Portable Stimulation and Assessment Tool (PSAT) effectively tests four sensory areas: tactile, visual, auditory, and olfactory.

How this project helped
According to Mary Caldwell, an OT in Pediatric Rehabilitation at Duke Hospital: “The stimulator allows us to to evaluate cognitive awareness and sensory status at bedside in one session, and from that to develop treatment strategies on extremely motorically involved patients.  Prior to this compact unit, a full assessment may have taken the therapist several consecutive trips to bedside.”

The PSAT (Fig’s 1, 2) is divided into four independent systems, which test four sensory areas: tactile, olfactory, visual and auditory.

The tactile probe is physically and electrically independent of the rest of the device. It utilizes a miniature vibration motor powered by a single AAA battery, encased within a penlight housing. A vibrating pager motor is used because of the small  size and low power requirement. The activation switch is the push-button of the original penlight.

The olfactory stimulation system uses an air freshener which is mounted flush to the back of the PSAT. The freshener is replaceable through the battery compartment. A mechanical slider opens small slits in the back of the PSAT to allow the scent to emanate from the cartridge.

The auditory, visual and LCD circuits (Fig. 2) are controlled by a Basic Stamp II microprocessor. A pushbutton switch updates the message displayed on the LCD screen, such as “blink your eyes”. A slide switch controls the backlight on the LCD     screen. Rocker switches activate the visual stimulation, melody generation, and intensity functions. A serial port is installed on the side of the device to reprogram the microprocessor. The intensity rocker switch controls the flashing rate of the visual system and the volume of the auditory system.

The visualization system comprises 19 LED’s arranged in a pattern of three concentric rings consisting of 1, 6, and 12 LED’s respectively per ring. The duration that each ring is lit differs depending on the state of the intensity switch: 200 ms for        low and 85 ms for high. A Darlington transistor relay powers the visual system.

The auditory system has three functions: melody generation, message recording and playback, and amplification. The record and playback is usually in stand-by state. When the melody generation function is activated, power to the record and playback function is removed to prevent distortion. The record and playback function allows a 20 s message to be recorded. The melody generation function uses a low power differential amplifier (LM386) designed for audio applications to    improve sound quality. One of three different melodies is selected using a slide switch.

The device is powered by 4 AA batteries in series, and consumes at most 150 mA. The device is contained within a 4″x7.5″X1.3″ plastic casing.  The total cost is $240.

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