make paths work also when executed via crontab

readSensor.sh

@@ -29,16 +29,17 @@ MAXTEMP=40
 # CMD should point to the compiled Adafruit binary that does the acutal reading from the sensor
 # See https://github.com/adafruit/Adafruit_Python_DHT for details
 # The 'sudo' is not needed if the user executing the script is member of the group 'gpio'
-CMD="sudo ${PWD}/external/Adafruit_Python_DHT/examples/AdafruitDHT.py"
+CMD="sudo ./external/Adafruit_Python_DHT/examples/AdafruitDHT.py"
 
 # Location where the readings should be stored
-OUTFILE="${PWD}/output"
+OUTFILE="output"
 
 
 #
 # no configuration/changes should be necessary below this line
 #
 
+cd "$(dirname "$0")";
 touch "$OUTFILE" 2> /dev/null
 
 if [ ! -w $OUTFILE ]; then