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3 LDR based Line Follower

3 LDR based Line Follower


As the name indicates, SLIM-BOT, is a small, simple, compact robot, which may be moved or controlled using various inputs, without using any micro-controller. There is no need of programming language or coding to make and control the Slim-Bot. This is the basic project for those, who don’t have any knowledge in micro-controllers and programming. The various controls for the Slim-Bot is completely based on the electronic circuits only.

Sometimes, IR sensor may misbehave due to interference from sun-light or other gadgets like IR remote etc. Using LDR may eliminate the external IR interference and more comfortable. More over IR light is invisible to naked eye. So, it is difficult to confirm that the IR LED is working properly or not.

To make LDR (Line Depending Resistor) based Line follower, two sets of, White light emitting LEDs (as Light Source) and Light Depending Resistors (as Light Sensors) are used on either side of a line, fitted on the front side of the Slim-Bot. The signal generated by the LDRs, based on the presence of the line, is fed to the two digital inputs of the 8 pin berg strip. The Slim-Bot moves forward or takes turn accordingly to move itself on the line.


About LDR sensing:

To make the Slim-Bot compact, two numbers of Light Sensor Modules / Boards are made for reading the presence of the line. Each Light Sensor Board contains, a White-LED and a LDR sensor, which are positioned side-by-side on a small PCB. A transistor with required current limiting resistor and connectors are used for each Light Sensor Board. A 100K trimpot (variable resistor) is used to adjust the output signal voltage. The trimpot has to be adjusted to get proper threshold voltage as input to D0 or D3 pins of 8 pin connector on the Slim-Bot. 

The complete circuit diagram of Light Sensor Module / Board is shown below.

When, the Light Sensor Board is connected to power supply (here it is 3.7VDC), then the white LED glows. Adjust the emitting light from white LED to reflect on the LDR, when placed above a white surface, at a small distance. The signal output may be observed by connecting a red LED across the signal output and ground. Adjust the trimpot, until, the red LED gets OFF on black surface and GLOWS on white surface.


Working of Line Follower:

Two such Light Sensor Modules / Boards are fitted on either side, in front of the Slim-Bot. The circuit diagram, connecting the two Light Sensor Modules to the 8 pin berg strip on base board, is shown below.

When, the output from Light Sensor Board gets high signal, due to white surface (reflected light from white-LED), then the motor on the same side rotates. Similarly, when the output from Light Sensor Board gets low signal, due to black surface (insufficient reflected light from white LED from black surface), then the motor on the same side stops rotation.

So, the motor on white surface side rotates in forward direction and the motor on black surface side (line is drawn in black colour) stops rotation. Thus, making the Slim-Bot to automatically re-position on the line. When both the LDR sensors are above the white surface, the Slim-Bot moves straight forward, continuously.

CLICK HERE to know, how to make BASE for SLIM-BOT.

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