Low frequency oscillator
Since I've been on some deep chorus dive lately, here is a circuit snippet from Boss CE-3 (and others): LFO or in other words triangle wave oscillator made of comparator (Schmitt trigger) and integrator.
In this configuration comparator output from op-amp pin 1. is somewhat square wave as seen on first oscilloscope picture. Triangular wave is taken from the integrator output from op-amp pin 7. and it's relatively good triangular waveform.
Oscillator frequency is determined by R7 and C3. Common mod for Boss CE-3 chorus pedals is to change C28 (here C3) from 100nF to 47nF like I've done here. This mod will increase the maximum frequency.
This is not the best possible triangular wave oscillator. But this is enough for effect pedals. And that's what counts. You can try this with tremolos too.