Digital Heart beat sensor

/*
* Project name:
Digital Heart beat sensor
* Copyright
(c) Researchdesignlab.com
* Test configuration:
BOARD: RASPBERRY PI & BEAGLEBONE
Software: ECLIPSE

*/

#PROJECT NAME:HEARTBEAT SENSOR
#PROJECT LANGUAGE:SHELL SCRIPT
#COPYRIGHT:RESEARCH DESIGN LAB(C)

echo 4 > /sys/class/gpio/export

echo in > /sys/class/gpio/gpio4/direction

count=0
k=0

while [ $k -lt 500 ]
do
x=$(cat /sys/class/gpio/gpio4/value)
if [ $x = 1 ]
then
count=$(expr $count + 1)
sleep 0.50
fi
k=$(expr $k + 1)
done
echo $count