= Ultrasonics =
* DEVICES: ultrasonic rangefinder sensor.
* THEORY: range finding, pulse measurement
* TOOLS: use oscilloscope or logic analyzer to observe/measure ranging
* HANDS-ON: Connect an ultrasonic rangefinder to the protoshield (power, ground, switch to trigger).  
   * Use Arduino to trigger ranging and measure result
   * Make an electronic tape measure
   * Make a Theramin.