relatively constant velocity. The entire assembly was placed upon the stairs, as seen in

Figure 4-2.






















Figure 4-2: Stair-counter testing assembly

 The system recorded a reading of the range data from the surface of the staircase to

the infrared sensor once every 50 milliseconds. This delay was chosen, as it is longer

than the 32-millisecond update rate of the infrared sensors and therefore ensured that no

duplicate readings were accidentally recorded by the system. The microcontroller then

determined the first derivative of the data, applied a three element median filter to it, and

then determined the second derivative. A Dell Inspiron 8100 laptop computer then

recorded this data set. Communication between the Dell and the Rabbit were made via

the 57.6-kBaud connection provided for diagnostic purposes by the microcontroller. The

test was run a total of ten times on two separate staircases.

 The stair-counter testing also had a secondary purpose: to empirically determine a

second derivative threshold value for the stair-counter control code. The stair-counter