Line Detector

Posted on Feb 5, 2014

One of the simplest ways to show autonomous motion of a robot is to have it follow a line. In fact there are competitions for the fastest or for robots that can follow complex line mazes. Lines are either high contrast black lines on a white background or white lines on a dark background. Following numerous other circuits in this area, the standard detector circuit is to use an infrared (IR) optical sensor and a voltage comparator.

Line Detector
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The IR sensor consists of an infrared LED and phototransistor side by side. The phototransistor outputs a variable voltage depending on the reflective surface that it is placed near. The comparator has the negative input connected to the IR sensor and the positive input connected to an adjustable voltage. By adjusting this voltage appropriately the comparator can output a low or high voltage depending on the reflective surface it is placed near. For this project I decided to use the commonly available Vishay TCRT5000 optical sensor. This sensor has its maximum output at a distance of 2mm (0. 08 ) but can operate in the range from 1mm to 12mm (0. 5 ). To make sense of the voltage output from different sources here is a table that I derived through experimentation: After doing some research using my favorite tool (Google) I found a number of documents are proved useful in building the circuit for my line detector. One document was the manual for the CBA Line Following Module that features multiple socketed detectors and a simple comparator circuit. Most line-following robots utilize more than one sensor. Here is an excellent article that discusses why multiple sensors are useful and how to use 2, 3, 4 or even 5 sensors. However the light from two sensors can cause false readings and therefore it is important that only one sensor is active at a time. It takes longer to get readings from all the sensors but the readings are...

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