The second part of this tutorial about the software can be found here:
What you need:
* 2 X pieces of wood 4X6. 1/4'' and the other 1/2'' thick
* 1 X 3 inches pipe. length varies depending of the deep of your pit.
* A couple of screw
* 1 X 1k resistor
* 1 X Raspberry pi
* 1X HC-SR04 ultrasonic sensor