Designing a simple and yet functional Line Follower Robot (LFR) is always a fascinating and challenging subject to be learned, the LFR actually could be implemented in many ways start from a simple two transistors to a sophisticated PID (Proportional, Integrate and Differential) which take advantage of the programmable feature of microcontroller to calculate the PID equation to successfully navigate the black track line on a white background surface.
Designing a non microcontroller based LFR is quite challenging tasks as we need to limit the electronic components numbers so the LFR will not too complicated to be built by most average robotics beginners or electronic hobbyists, but at the same time we need to have a good speed control mechanism in order for the LFR to navigate the black track line successfully. The microcontroller based design LFR in the other hand is a popular choice because it reduces a number of electronic components significantly while still providing a flexible programmable control to the LFR.
On this tutorial we are going to build yet another LFR using just the standard analog components easily found on the market but use the same speed control method technique found in many good microcontroller based Line Follower Robot design. As the result we could get a good precision analog line follower robot that comparable to the microcontroller based Line Follower Robot design. On this tutorial you will also learn many useful information of how to use the operational amplifier.
The Line Follower Robot
This Line Follower Robot basically use a Cadmium Sulphide (CdS) photocell sensor or known as Light Dependent Resistor (LDR) and the high intensity blue Light Emitting Diode (LED) to illuminate the area under the photocell sensor to sense the black track line and the DC motor speed control technique to navigate the black line track as shown on this following picture:
The easy method to navigate the black track line is to turn ON and OFF the left or the right DC motor according to the sensor reading (black turn OFF and white turn ON), but using this method will make the LFR to move in zigzag way. By proportionally control both left and right DC motor speed according to the light intensity level received by the photocell sensor (reflected back by the black track line) we could make the LFR easily navigate this track. The common technique to control the motor speed efficiently is to use a pulse signal known as the pulse width modulation or PWM for short.
PWM basically is an ON and OFF pulse signal with a constant period or frequency. The proportion of pulse ON time to the pulse period is called a “duty cycle” and it expressed in percentage. For example if the proportion of pulse ON time is 50% to the total pulse period than we say that the PWM duty cycle is 50%. The PWM duty cycle percentage is corresponding to the average power produced by the pulse signal; the lower percentage produces less power than the higher percentage.
Therefore by changing the PWM duty cycles we could change the average voltage across the DC motor terminals, this mean we could vary the DC motor speed just by changing the PWM duty cycle. Therefore to make the LFR smoothly navigate the black track line, we have to adjust the PWM duty cycle according to the photocell sensor reading. The brighter light intensity level received by sensor (sensor is on the white surface) will result in higher PWM duty cycle percentage and the darker light intensity level (sensor is on the black line) received by photocell sensor will result in lower PWM duty cycle percentage.
Read more: The LM324 Quad Op-Amp Line Follower Robot with Pulse Width Modulation