Penn State
Electrical Engineering
Spring 2002
Group Members: EunJung Kim, Peyman Safabakhsh, Scott Bellows, Greg Van Orden
Abstract: A severely disabled three-year-boy is
unable to use the educational toys made for other children of his age. Our
design improves on many conventional toys' shortcomings and packs several useful
features in one easy to use toy. This toy will be used to teach the child
"cause and effect." Since the child is not able to exert enough
force to operate conventional toys, our design includes a button that uses a
touch sensitive charge transfer sensor integrated into a very sensitive
mechanical switch that can be enabled once the child gains better control of his
arm. Sound volume control and light motion speed control provide the therapists
the options for setting a safe operation mode. The light display is bright
and colorful to keep the child interested. Since the child has difficulty
following motion, the light display will move in a continuous fashion. Our
sound circuit design is able to record music clips as well as human speech for
extra customization. This design once implemented will be aesthetically
pleasing, practical, reliable, and fun.
Specifications:
Dimensions: 11.5 x 10 x 2.5 inches
Power: 4 D cell batteries are required
Theory:
The button was designed with two means of activation. The first is a charge-transfer sensor and the second a micro-switch. The reason there are two methods of activation is to provide an added challenge after the child has learned ‘cause and effect.’ The touch sensor will simplify the child’s task of activating the toy. When he learns that his action or touching the button activates the toy, the challenge of physically pressing the micro-switch can be added.
The QProx QT110 chip, the charge-transfer sensor, was chosen because of its simplicity in design and the amount of flexibility it allows in the physical design of the button. The QT110 is a self-contained digital IC capable of detecting near-proximity or touch. It will project a sense field through a maximum of 8mm of almost any dielectric material. The QT110 was specifically designed for human interfaces like toys and appliances or anywhere a button may be found. A sensing electrode is used to project the field and may be any size or shape. The metal electrode will be placed just underneath the button, which is less than 8mm thick. This will allow the button surface to be plastic instead of the metal electrode.
In order for our toy's light display to capture the child's attention, the lights were designed to be large enough and bright enough to compensate for his limited vision. Since our toy is battery powered, the lights need to operate efficiently and as in any other product, durability is desired. In comparison with conventional small light bulbs, LED arrays provided better characteristics in virtually every category. The only shortcoming of the LED's is their highly directional light beam. In order to compensate for that, a highly dispersive cover will protect the lights.
The ideal controller for a sequence of lights is a logic state machine, due to its ease of implementation and easily controllable motion speed through a variable clock. The clock speed is changed using a sliding rail to allow the therapist to set a safe traveling lights speed. A fader circuit has been included with each LED array to make smooth transitions between arrays. The variable light speed and smooth transitions between lights will help prevent Jonathan from having seizures.
Considering the ease of operation and low power usage of digital sound chips versus analog tape recording and playback, the group chose the digital approach. Since recordable sound chips allow for further customization at little or no surcharge, a sound chip capable of recording 20 seconds of music was chosen. Due to the child’s hearing impairment, the group deemed the output volume of the sound chip insufficient. An audio amplifier was added to raise the volume to the desired range and to provide a volume adjustment feature. Since the music playback time is variable, the ending of the light sequence needed to be controlled by the sound chip. Some additional logic was added to synchronize the two modules.