Child Friendly Timer

Designers: Sean Breit, Stephanie Liu, and Srinivasan Yegnasubramanian
Client Coordinators: Lenora Champion
Supervising Professor: Dr. Larry N. Bohs

An electronic timer was constructed for use in pediatric therapy sessions. Presently, for timed sessions, a therapist sets an electronic kitchen timer that beeps when time is finished. However, most young children do not have a clear concept of time and cannot understand how much longer their practice sessions should continue. The Child-Friendly Activity Timer (CFAT) was created to provide these children with a visual and qualitative measure of time during their therapy sessions. The CFAT features a small rabbit moving across a hill toward its burrow, and a digital display that shows the time remaining for the therapist. When time expires, a beeper sounds and the rabbit returns to its starting location.

How this project helped
The client is a two-year-old with a feeding disorder. Part of the client’s prescribed therapy includes timed feeding sessions, where he is required to practice activities such as holding his spoon and drinking from a cup for specific periods of time. The CFAT helps the client understand how much time remains in his therapy session, and when the session is over. Other children at Duke Hospital also benefit from this device in timed therapy sessions.

The CFAT is a microprocessor-controlled device that contains both a numerical and physical display of the progression of time. The user programs the CFAT using six pushbuttons. Three buttons set the time in increments of 30 seconds, one minute, and ten minutes. The other three buttons start, stop, and clear the timing process. The microprocessor reads from these six pushbuttons and controls the time displayed on a 4 ½ digit LCD 7 segment display as well as the movement of a toy rabbit, attached to an arm on the shaft of a servomotor.
The CFAT consists of three sections: 1) input acquisition; 2) time and display processing; and 3) numerical and physical display (see Figure 2). The input acquisition section contains the pushbutton hardware and the software required to process user input. The pushbuttons connect to the data lines on a Z-180 microprocessor (Z2 Prototyping board, Zworld, Inc, Davis, California) through a tri-state latch (74HCT373). The six-bit binary number representing the state of the pushbuttons is translated into an instruction by the microprocessor. The program contains de-bouncing routines that prevent the microprocessor from reading unintentional input. Additionally, the input software prevents the user from making logistical errors, such as accidentally clearing the time remaining during operation without first stopping the timer.

The time and display section controls a countdown timer and the servomotor. The countdown timer uses the real-time clock on the Z2 board to calculate the time remaining. The servomotor is controlled using an 8-bit binary number that increases at a constant rate determined by the input time. This binary number is converted into an analog current using a digital to analog converter (DAC0832), and then converted to a voltage using a single-sided operational amplifier circuit (LM358). This varying voltage is translated into a square wave with linearly varying pulse width using a voltage controlled oscillator (CD4046). The square wave is connected to the control line of the servomotor. The servomotor moves through 30 steps over an angle of 120o.

The output section comprises a numeric display, a physical display and an audible buzzer. The time is displayed on a Varitronix 4 ½ digit LCD display. This display is controlled using 32 serial bits from a MM5452 controller chip. The serial clock and count data are generated by the microprocessor. The physical display is a toy rabbit attached to the shaft of the servomotor. To conserve power, a transistor switching circuit turns off the servomotor whenever it is not being moved. This feature dramatically reduces power consumption since the servo motor only operates for 30 seconds, regardless of the input time. Finally, a small buzzer sounds when the time is finished.

The CFAT uses four C batteries in series to provide a 6V DC supply, which powers the servomotor and the buzzer directly. The 6V DC is regulated to 5.2 volts to power the microprocessor and the other IC’s.

The final cost of the Child Friendly Activity Timer was approximately $380.

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