Using a single supply quad comparator LM339, LM239, LM2901, LM2901V, NCV2901, or MC3302, we can build a square-wave oscillator with simple circuit and formula. Here is the schematic diagram:

square oscillator using comparator circuit schematic diagram

We can build a square-wave oscillator with simple circuit and formula, using a single supply quad comparator LM339, LM239, LM2901, LM2901V, NCV2901, or MC3302. Following figure shows the circuit schematic diagram :

When you need  many square-wave oscillators in one circuit, this circuit is very usable since the quad packaged comparator provide four comparators in one single  integrated chip. [ source: Motorola Application Notes]