Line Follower

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Contents

Kit Contents

The line tracker kit consists of three sensor modules. 

Linetracker.jpg

Functions

A line tracker mostly consists of an infrared light sensor and an infrared LED. It functions by illuminating a surface with infrared light; the sensor then picks up the reflected infrared radiation and, based on its intensity, determines the reflectivity of the surface in question. Lightly colored surfaces will reflect more light than dark surfaces; therefore, lightly colored surfaces will appear brighter to the sensor. This allows the sensor to detect a dark line on a pale surface, or a pale line on a dark surface.

Benefits

The line tracker allows your robot to follow a pre-marked path and allows humans to indirectly control the robot while it is autonomous.

Applications

The line tracker enables a robot to autonomously navigate a line-marked path. By drawing a line in front of a robot outfitted with a line tracker, one can dictate the robot’s patch by showing it where to go without using a remote controller. A typical application uses three line trackers, with the middle sensor aligned directly above the intended line.

Range Limits

The range for the line tracker is approximately 0.02 to 0.25in (from the ground) with optimum sensitivity at 3 mm (about 1/8 inch). The minimum line width it can detect is 0.25in.

The line tracker is an analog sensor, meaning that it can output many more values within its range of potential values (in this case, from 0-5V) than a digital sensor, which would output only a handful of discrete values in the range (e.g., 1, 2, 3, 4, and 5V), as is the case for a digital sensor. This range of output from 0-5V is sent to the microcontroller, which translates it into a corresponding range of integer values from 0 to full scale. Full scale is 1023 for 10-bit Analog-to-Digital values such as with easyC or ROBOTC for PIC, 4095 for 12-bit values such as with ROBOTC for Cortex and 255 for 8-bit values such as with MPLAB. When using the Cortex Microcontroller, typical white/black/"away from everything values" will be 38/662/770 for easyC, 153/2650/3076 for ROBOTC and 9/166/192 for 8-bit values. When using the PIC Microcontroller, typical white/black/"away from everything values" will be 38/882/1012 for both easyC and ROBOTC and 9/220/253 for 8-bit values

For this particular sensor, the output will be low when the surface is pale or highly reflective and high when the surface is dark and absorbs infrared energy.

Note:There is an error on the Inventor's Guide insert packaged with older Line Follower Kits. It calls out an optimal range of 0.02 - 1.0 inches. The optimal range is 3 millimeters.

Technical Information

  • Sensor Type
    • Infrared light sensor and infrared LED
  • Line width
    • 0.25in minimum; optimal line width is 0.5in
  • Optimal Range
    • 3mm (just under 1/8in), effectiveness drops off by approx. a factor of 10 at 5/8in
  • Response Frequency
    • 50Hz
  • Light Source
    • GaAs infrared LED with a peak wavelength of 940nm
  • Receiver
    • Si phototransistor with a sensing wavelength of 850nm (max)
  • Wiring
    • Black - ground; Red - (+) power; White - control signal



ROBOTC Sample Code

Linefollower.png

CMU Robotics Academy Resources


easyC Sample Code

Line Follower Figure 2.jpg