Servo - May 2012

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The Sensor Olympics 2 – Going the Distance

THE SCRIBBLER IS LOOKING TO TURN ITS OPENING VICTORY INTO A WINNING STREAK.

www.servomagazine.com/index.php?/magazine/article/may2012_TwinTweaks

Last time, we pitted some members of our robot menagerie against each other in a thrilling contest for infrared sensor supremacy. The slow and steady the line following sensors, the components themselves lacked any identifying information that might lead to a datasheet or other specifications. The official Scribbler information from Parallax is also less than illuminating – the Scribbler page describes the sensors as IR phototransistors, and the schematic does not indicate whether the sensors are implemented as digital or analog inputs. We wanted to know whether the sensors were used as digital or analog inputs because that would affect the way we

Open Rangefinder

Obstacle avoidance sensors are a popular feature for robot kits. A classic ingredient for a maze navigating bot, obstacle avoidance sensors generally work by sending out some sort of pulse, waiting for it to reflect off of an obstacle, and sensing the reflected pulse. The strength and delay of the reflected pulse give valuable clues as to the distance of an obstacle. The Scribbler and the Mark III both come with a classic solution for obstacle detection: infrared sensors. Both robots use a combination of infrared transmitters to send out a beam of infrared light and an infrared detector to sense the reflected beam. The Scribbler uses transmitters and detectors that are mounted in the very front of the bot, while the Mark III uses the extremely popular 2YOA21 Sharp rangefinders. Before we devised some tests for the sensors, we wanted to get a bit more acquainted with them.

The Scribbler obstacle avoidance sensors are a bit more accessible than the line following sensors, and can be reached simply by removing the Scribbler’s lid. Much like