A comparator circuit, in general, contains a threshold (reference) voltage to which another
signal is compared. If the signal is greater than the reference voltage, the
output voltage of the comparator is 
. If the signal is less than
the reference voltage, the output voltage of the comparator is 
.
In the controller circuit the comparator (comparator 1) is used to shift the Levels of the square wave from 0V and 5V to -5V and +5V.
The output of the J-K flip flop is a voltage square wave with Levels
of 0V and 5V. This square wave is the input to the comparator.
The comparator circuit utilizes one of the 741 op-amps on the LM324
Quad Op-Amp chip shown in Figure 
.
The purpose of the comparator in this circuit is to shift the
voltage Levels of the square wave produced by the flip flop to the power supply
Levels (
) of the op-amp. This change in amplitude creates a
square wave signal that is symmetric around ground (ideally) but does not affect the shape or
frequency of the square wave input signal. Hence, the output of the comparator is also a
square wave, but its voltage Levels have been shifted from 0V and 5V to
-5V and +5V.