1. Crib Pediatric Dynamometer Abstract Many researchers are currently studying the activity of infants in search of a relationship between energy expended at an early age and the increasing obesity epidemic. Collecting meaningful data in this area has many obstacles. Current data acquisition techniques are very complicated, costly, limited by age, and unnatural for the subject. The idea of monitoring an infant’s activity in a crib with the use of piezo sensors bypasses some of the obstacles found in current methods. An array of sensors that cover the area of a crib mattress continuously measures changes in the force applied by the infant. A master-slave microcontroller configuration is used to sample each of the sensors. Each slave microprocessor samples a column of sensors and the master microprocessor collects data from each of the slaves. This master- slave configuration allows for easy expansion of the system to meet different sizing needs. All data is serially communicated to a computer from the master microcontroller. At this point, the data can be processed on a computer and analyzed through a graphical user interface allowing the researcher to visually and analytically examine the data. Group 12 Authors Brian Dodd EE ’07 Stephen Lin EE ’07 John Shon EE ‘07 Advisors Dr. Jay Zemel Dr. Babette Zemel Demo Times Thursday, April 19, 2007 10:00-12:00PM, 1:00-1:30PM University of Pennsylvania Dept. of Electrical and Systems Engineering Computer Master PIC Slave PIC Signal Conditioning GUI Graphical User Interface The Master PIC feeds data from the sensors to the computer by serial communication via USB. The GUI is built in Matlab, which will process the data from its raw format into a force reading using the calibration curve and the following formulas: The data is then graphed in a three- dimensional bar graph while being written to a file on disk simultaneously. Graphical User Interface The Master PIC feeds data from the sensors to the computer by serial communication via USB. The GUI is built in Matlab, which will process the data from its raw format into a force reading using the calibration curve and the following formulas: The data is then graphed in a three- dimensional bar graph while being written to a file on disk simultaneously. Signal Conditioning Circuit The signal conditioning circuit serves two primary purposes: multiplex the sensor array and prepare the signal for the slave microcontroller input. The multiplexing is performed by an 8-to-1 analog chip controlled by the slave microcontroller. The signal is then amplified to maximize the use of the available quantization levels of the A/D converter in the microcontroller. The last step involves offsetting the signal by 2.5V so that it is in the middle of the voltage range of the microcontroller. The layout of the signal conditioning circuit is given below. Signal Conditioning Circuit The signal conditioning circuit serves two primary purposes: multiplex the sensor array and prepare the signal for the slave microcontroller input. The multiplexing is performed by an 8-to-1 analog chip controlled by the slave microcontroller. The signal is then amplified to maximize the use of the available quantization levels of the A/D converter in the microcontroller. The last step involves offsetting the signal by 2.5V so that it is in the middle of the voltage range of the microcontroller. The layout of the signal conditioning circuit is given below. Master-Slave PIC System Data collection from each of the sensors is controlled and exported through a master- slave PIC scheme. Sampling of each of the 8 sensors in a column is controlled by a slave PIC16F88 microcontroller, and the 8 data bytes are saved in the PIC. When each of the slave microcontrollers have acquired their samples, the master PIC16F690 microcontroller coordinates the orderly transfer of data from each of the slave PICs to the master PIC. Once data has been acquired from each of the 72 sensors, the master PIC sends the time stamped data through an Rx-Tx line to a USB serial port for recording and processing on the computer. The entire board of sensors is sampled and the corresponding data sent to the computer every 5 milliseconds. Master-Slave PIC System Data collection from each of the sensors is controlled and exported through a master- slave PIC scheme. Sampling of each of the 8 sensors in a column is controlled by a slave PIC16F88 microcontroller, and the 8 data bytes are saved in the PIC. When each of the slave microcontrollers have acquired their samples, the master PIC16F690 microcontroller coordinates the orderly transfer of data from each of the slave PICs to the master PIC. Once data has been acquired from each of the 72 sensors, the master PIC sends the time stamped data through an Rx-Tx line to a USB serial port for recording and processing on the computer. The entire board of sensors is sampled and the corresponding data sent to the computer every 5 milliseconds. Sensor Array An array of Measurement Specialty’s LDT2-028K piezo film sensors is used to detect activity. When the sensor is subjected to a change in force it generates an external current. An example waveform from the output of the sensor when it is tapped is given below. The output from the sensors had to be calibrated against actual force data as a layer of padding is placed on top of the array. A Pasco Scientific CI-6618 Force Sensor was used to log force data. The maximum force from the force sensor was compared against a value obtained by integrating over the range of activity from the output of the piezo film sensor. A calibration curve was created using this data and is found below. Sensor Array An array of Measurement Specialty’s LDT2-028K piezo film sensors is used to detect activity. When the sensor is subjected to a change in force it generates an external current. An example waveform from the output of the sensor when it is tapped is given below. The output from the sensors had to be calibrated against actual force data as a layer of padding is placed on top of the array. A Pasco Scientific CI-6618 Force Sensor was used to log force data. The maximum force from the force sensor was compared against a value obtained by integrating over the range of activity from the output of the piezo film sensor. A calibration curve was created using this data and is found below. Amplifier Sensors BufferOffset A/D MUX Force Applied Force Removed Sensors Slave PIC Signal Conditioning Sensors Slave PIC Signal Conditioning Sensors O O