IR Line Following Sensor
IR stands for Infrared. A Line Follower Robot (LFR), needs a sensor for detecting the line which is in contrast with the surface over which the bot grazes. This line sensor can be easily made using cheap IR (infrared) pair. The IR Tx (transmitter) emits IR radiations and the Rx (receiver) helps to recieve it. the circuit shown at the end worked well in my Arduino LFR without much disturbance by ambient light around.
How the IR pair looks : 
The blue coloured one is the Tx, while the white one is the Rx. In some cases Rx is also black coloured. The longer connecting lead is the anode (positive) while the shorter one is the cathode (negative) for both.
Checking an Infrared Transmitter :
You can check whether a Tx is OK by connecting to a supply and viewing it through a mobile camera, you will be surprised to see a violet-pink light which otherwise you cannot see through naked eyes. **Check doing the same with your TV remote IR in the front**
Checking an Infrared Receiver :
This is a methodof checking whether an IR Rx by resistance method.
Final Schematic for Line Sensor :
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