.. 6.4

Distance Measurement, by ultrasound echo
========================================

**Objective**

Measure distance by measuring the time taken by :math:`40~kHz` pulse train to
echo from a hard surface.

**Procedure**

.. image:: schematics/sr04-dist.svg
	   :width: 300px

-  Keep a flat surface, like a cardboard sheet, around 10 cm from the
   echo module
-  Press START
-  Change the distance with time

**Discussion**

The distance is calculated from the time taken by a burst of sound to
echo from the surface kept in front of the module. The distance can be
measred as function of time, enabling to calculate velocity,
acceleration etc.
