The IR board consists of 4 pairs of IR emitters and receivers.
The comparator used is LM324 (quad comparator).The threshold voltage at which the comparator triggers is set by a potentiometer.
The sensors are not modulated,so their range is restricted to about 5 cm(which is sufficient for following a line).
Whenever a receiver detects an IR signal,the respective LED glows.
A signal is sent to the Micro Board,which takes necessary action.
The output voltage from the sensor board is not more than 5v.


Related items : The circuit used can be found here

Related items : Download the LM324 comparator datasheet from here