Crib Pediatric Dynamometer

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 infants 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

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.
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.
Computer
GUI
Master PIC
O O O O
O O O O
Slave PIC
Slave PIC
Slave PIC
Signal Conditioning
Signal Conditioning
Signal Conditioning
Sensors
Sensors
Sensors
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.

Sensor Array An array of Measurement Specialtys
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.
Force Applied
Force Removed