The first OpAmp works as a square wave generator, the other two work as integrators. An integrated square wave results in a triangular wave. Then again, the triangular wave is integrated, which reaults in a sinusoidal wave. The last OpAmp is an inverting output amplifier, which scales the signals to the right amplitude. With the three switches you can choose between the three wave forms. To start simulation, you need to inject a noise. To do so, shake phone.
