Pediatric Dynamometer ABSTRACT The Children’s Hospital of the University of Pennsylvania has long been involved with the study of the correlation between obesity or bone density and youth exercise. In 2004, the Pediatric Dynamometer was born as an engineering project in the Moore School of Electrical Engineering. Current measurements of exercise are not capable of conveniently delivering the main metric by which correlation should be measured: exerted force. The Pediatric Dynamometer has been developed to provide a comfortable, durable modification to any youth’s shoes to allow for accurate measurement of force exerted by the foot over extended periods of time. The full implementation of the design consists of an inside-shoe embedded system, which receives signals provided by a Piezoelectric sensor and processes them in an on-board microcontroller. The control system contains algorithms for uploading the data into a computer for processing and storage. The sensor and inside component are installed within the shoe in an unobtrusive fashion. A prototype of the shoe which is fully functional and possibly marketable for athletic shoe applications is ready for demonstration. AUTHORS Armand O’Donnel Kevin MaADVISORS Jay Zemel Professor Emeritus University of Pennsylvania Group #9 Department of Electrical and Systems Engineering Top of PD Circuit (Digital Layer) Bottom of PD Circuit (Analog Layer) Circuit and battery mounted on foam rubber. Sensors are mounted on spring steel and sealed with silicone. Cable connecting PD to a computer. USB cable contains rs-232 converter. We added a 3.3V regulator to power the PD in the event of battery expiration. Below Minimum Threshold? (2) Update: Max Force Avg. Force Timestamp Write to Flash Memory Above Minimum Threshold? (1) ADC Data From Instrumentation Amplifier, x[n] NONONONO YES YES NO Integrate Signal y[n] = y[n-1] + x[n] Continue Integrating Pack Data into 10-byte Packet Progression of PD Circuitry over the years. Sensors used: 2x polyvinylidene diflouride strips Placement Of Sensors: One under heel of foot One under ball of foot Comfort: Layers of foam rubber are inserted above and below circuit. Protection: Sensors and circuit are mounted using waterproof silicone Shoe Integration Uses simple methods to communicate through a chosen COM port to retrieve information from the chip and issue commands Methods: Record Data – Retrieve sampled data Begin Sampling – Initialize force sampling Clear Memory – Clear stored data on chip Save Data – Save data recorded from the chip in a text file for easy analysis with excel Graphical User Interface Size: 1.4” W x 1.1” L x 0.3” H Power Consumption: 450 microWatts Power Source: 3.3V, 540mAh Lithium Battery Battery Size: 1” dia x 0.2” H HardwareSpecifications Force: Algorithms: Digital integration: add each sample to accumulator Accumulator value is current force Intelligent algorithm clears accumulator if necessary Peak and average force, timestamp saved to flash Thresholds: Algorithm uses min/max thresholds and hysterisis to prevent incorrect step detection, which would write spurious data to flash. Sampling Theory PIC16F690Microcontroller 16Mbit Flash Memory DataArchive PVDF PVDF Sensor Sensor PVDF PVDF Sensor Sensor InstrumentationAmplifiers Inside Shoe 200 Samples Per second 3.3V Button Cell Battery Khz Watch Crystal GraphicalUserInterface Sleep Mode USB to RS-232Converter