Line Following Basics


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There are a number of ways to set up the course for a line following robot. It can be a black line on a white background or the reverse. Either way, the robot is "trained" to use sensor readings to detect the line and follow it by adjusting the course and/or speed of the robot.



Selecting the Sensors

I've used the QRD1114 sensor before and I like it. I would recommend it to those who like building their own circuits from scratch. It looks like this:

It is cheap, accurate and fairly easy to set up. It is just the IR transmitter and a phototransistor receiver with no electronics, so the user must set up the circuitry on a printed circuit board or proto-board. Here is a typical set-up schematic:


How Many Sensors?

Once you decide on the sensor, the next decision is to decide on how many sensors are required to do the job. With no consideration for speed, one or two sensors are sufficient. The problems with this approach become apparent when the robot speeds up. As speed increases, turns come faster and the robot reaction time must improve. But then comes the question - - How many sensors are enough???
I'm working on another project with a different microcontroller where I built an eight-in-line sensor array, so I wanted to experiment with fewer sensors. So I needed a number between three and eight. I picked five, an odd number, so that when the robot is on track, it is only over one sensor. The argument could be made that six sensors spaced close together can also be effective. Anyway, for no particular reason, I picked five over six sensors.


The Line Following Algorithm

A line following robot with five sensors only has a limited number of possible combinations (assuming no read error). If the sensors are spaced such that only one sensor is normally over the line at one time, then the combinations are limited to these: