Line follower Robot - without using Microcontroller!!

Difficulty Rating : 3/10

Ever wanted to make a Line follower Robot, 'without' using  Microcontroller ???
Then you have visited a right place.

Inspiration:

I stumbled upon this Robot in my First year of Engineering during one of the Intercollegiate Robotics Championship (Regional) and ever since, it was my dream to make this Robot on my own. I googled for it & got many designs, but all Microcontroller based. I even shortlisted a few but my senior Pratik Kamat asked me take small steps first and suggested me to make one without the use of Microcontroller and with self designed logic.

Now, as a part of Electronics workshop in Sem-IV (II Year), we were supposed to make a project based on 'Electronics'. Since I was introduced to Microcontrollers at that stage, I made a proposal to make a Microcontroller based LFR( Line follower Robot). But it was rejected by my Batch in-charge as no microcontroller based projects were allowed for current semester. So i decided to make a LFR without using microcontroller. So, started the designing...

And to my surprise, the design was not that tough as it looks. All my friends loved it, batch in-charge appreciated it & (what startled me was the fact that) my immediate Seniors couldn't understand the working at all !!!!

Components : 

• High power LED (5mm) - 2 to 4
• LDR's -2 to 4
• Preset 20k -2 to 4
• 220 Ohm Resistors -2 to 4
• L293d -1
• Geared motors -2
• Chassis
• 4.8V NiMh rechargeable battery
• Burg strip, 2 pin relimat & other secondary stuff..

Circuit diagram:

The Circuit diagram with two pairs of LED-LDR. Click on the image for full-size version.

Click Image for Enlarged View

The Circuit diagram with four pairs of LED-LDR. Click on the image for full-size version.

Click image for enlarged view

Click image for Enlarged view

Working principle:

Our 9th grade science book has taught us that, when light falls on white surface, it gets reflected. When it falls on black surface (or any dark surface) light gets completely absorbed by it. How is this concept applied here? The sensor module has two LED-LDR sensor pair mounted on it (Minimum two is required. You can use any number). The LED or light emitting diode is a semiconductor light source which we will be using. I had used a 5mm white LED for my project. Also, LDR or Light dependent resistor is used here as a Light sensor. It senses the reflected light; i.e light transmitted by the LED and reflected from the surface. If the surface is white, LDR will detect the light. In case the sensor is placed over black surface, LDR cannot detect any light, as the black surface has absorbed all the light.

How Robot follows Line:
(Here I have used two LED-LDR sensor pair instead of four)

Please try to understand that the Left sensor-pair is connected to the left Motor and Right sensor-pair is connected to the right Motor. Notice that the sensor (Either left or right), from which the arrow is pointing outwards is our white LED (transmitter) which emits white light and the one on which arrow is pointed to is LDR or Light dependent resistor (Receiver). This LDR detects the amount of light that will get reflected from the surface, depending on whether the surface is white or black-line.

Straight

Left turn

Right turn

How it Works:

This Line Follower Robot basically use a Cadmium Sulphide (CdS) photocell sensor or known as Light Dependent Resistor (LDR) and the high intensity white Light Emitting Diode (5mm LED) to illuminate the area under the LDR sensor to sense the black track line. The LDR will decreases its resistance in the presence of light and increase its resistance in the dark. The region under the LDR is illuminate with a high intensity white LED, the white surface will reflect most of the light to the LDR surface while the black track line will absorb most of the light, therefore less light will reflect to the LDR surface. The 20KOhm trimpot and LDR basically is the voltage divider circuit. When the LDR detects the black track line it will receive less light intensity (LDR resistance increase). Result, the geared DC motor will turn slowly or stop. When the LDR on the white surface it will receive maximum light intensity (LDR resistance decrease) . Result, the geared DC motor will turn fast.

The IC L293D is a motor driver IC, used for boosting current levels, large enough to 'drive' the DC motors.

This is the pic of my 1st prototype using Breadboard (2 LED-LDR sensor)

The sensor mounting

Here's the video of my first Test-Run :

                                         


Feel free to comment if you are stuck up, or want to know more about its designing aspects, or if you find any bugs in the circuit diagram.