Circuit Project Electronic

The circuit has both square-wave and triangle-wave output. The left section is similar in function to a comparator circuit that uses positive feedback for hysteresis. The inverting input is biased at one-half the Vcc voltage by resistor R4 and R5. The output is fed back to the non-inverting input of the first stage to control the frequency.
The amplitude of the square wave is the output swing of the first stage, which is 8V peak-to-peak. The second stage is basically an op amp integrator.
The resistor R3 is the input element and capacitor C1 is the feedback element. [...]

Related Links
More Circuit about Function Generator
Squarewave Oscillator by IC LM339
XR2206 Function Generator.
8038 Tri-Waveform Generator (Easy Oscillator Generator)
Waveform Generator with ICL8038
Triangle and Squarewave Generator
Function Generator by IC 1458

Read more Source:

http://www.circuitsuggest.com/single-supply-function-generator.html