This circuit generates a stairstep waveform by an ingenious combination of 3 circuit elements:
- a "high" (265Hz) frequency pulse (555 timer) provides the charge to step-up the output
- the step pulse feeds an OpAmp pulse integrator/accumulator
- a low frequency pulse generator (OpAmp oscillator) provides the reset pulse that clears the accumulator and resets the 555
As always, all notes, schematics and code are in the Little Electronics & Arduino Projects repo on GitHub.