I need to create the simplest rectangular and triangular signal VCO I can using op amps. The output frequency should be changeable between 1k and 15k. I should also be able to change the amplitude of rectangular signal between 2 and 4 V. The triangular has to have the amplitude 5V. I was hoping I could modify this circuit by adding a DC voltage source somewhere to the V- input of the integrator, but I don't know how or if that's the answer to my issue. Can this circuit be modified for what I need or am I wasting my time and should look for something else?