This is a simple circuit using only one IC, a TL084 quad opamp. The integrator integrates the output. When the output is positive the integrator integrates in a negative direction. When its output goes below a selected negative value the output switches to negative. That makes the integrator integrate in a positive direction until its output goes above a selected positive value. That makes the output switch to positive again and the integrator integrates negative again. It does this continuously. Hence the integrator produces a triangle wave. The symmetry is fine-tuned by trimpot R4 which adjusts the midpoint bias of the circuit.

I operate the circuit from +12V. Since this may come from a noisy +12V switching power supply I provide some filtering with R2 and C2.

When I first set it up to measure THD+Noise with ARTA software (http://www.artalabs.hr/ I was getting only 8%. Wrong. Then I saw that I was clipping the triangle wave.

Clipping a triangle wave makes it more sine-like. This is the principal used by the XR2212 and ICL8038 (Intersil) and MAX8038 (Maxim) function generator ICs, only they clip their triangle waves in segments. They were all discontinued years ago. Although you can still buy them from companies in China (through eBay) I suspect that they are counterfeits. (But the ones I bought worked fine.)

As measured by ARTA Audio Measurement and Analysis Software the THD+Noise is 11.93% which is about right for a symmetrical triangle wave. The theoretical value is 12.1%.

The square wave output produces a THD+Noise of 42.98% which is about right for a symmetrical square wave. The theoretical value is 48.3%. Mine is lower probably because the edges are not as sharp as they could be.

Before finding ARTA I had been using a different spectrum analyzer program and I did not believe the results for THD+Noise. I decided to make my own triangle wave with the ability to tweak the symmetry. And I wanted something I could hold in my hands and which would produce an actual signal, not a simulation.

If you are not already a Maker (and you want to be one) see my tutorial on Making Things at www.jmargolin.com/making/jm_making.htm

JM