White Line Following
by Stephanie Adeyemo
The micromouse must be capable of following a rectangular track on a matte black background according to the dimensions of the track laid down in the rules for the IEE "Formula 3" Schools Micromouse web site.
The micromouse was able to give a clear indication when the the floor beneath it was black or white using a white line sensor. The Light Dependent Resistor was used to sense a white or black background. When the sensor is on a white line, it illuminates strongly and the resistance decreases to a few hundred ohms and when on a black surface, the resistance is high. A potential divider was used to convert the change in resistance into a change in voltage. Therefore on a white line (low resistance), the output voltage is low and on black suface (high resistance), the ouput voltage is high. The output voltage was then fed into an analogue input which converts it. The voltage at which the white surface transitioned into a black surface was called the threshold while programming the decisions to be made.
The circuit above is the circuit that was used as the simple white line sensor because it is a simple circuit and it is easier to programme with. Our micromouse made use of three white line sensor circuits all situated at the front right, front middle and front left of the micro mouse. The LED was used to reflect light on the backgorund surface. A white LED was used for each of our sensors because of its easy visibility during its initial testing on the breadboard as well as during circuit testing after soldering. From testing, our average threshold gotten was 3.5V.
During the testing of the three white line sensors, one major challecge was deciding the best positions on the micromouse to place the sensors because its movement on the track board had to be taken into consideration. Also, taking notes of the voltage measurements while testing th sensors when over a white of black surface. These measurements were of great use to our programmers who ensured a decision was made in the programming codes when the output voltage was greater or less than the threshold.