Working (?) PWM circuit by operation amplifiers

Last time I concluded that playing with high voltage AC was a bit too dangerous. Therefore I decided to consentrate low voltage pulse width modulation. Below is a picture-link to a good PWM page.


Yes, I shamelessly copy-pasted other peoples work here. The above picture is a good example of a PWM modulation circuit. The first two operation amplifiers (the leftmost triangles) produce a saw-tooth wave which is thresholded by the bottom op-amp and switched on/off with the fourth. This circuit includes all the basics what you need to know about operation amplifiers. We have inverting and non-inverting amplification, negative, (sort of positive,) fast and delayed feedback.

I was building this to test whether I remember how to use op-amps, but I ran into a problem. I don't have an oscilloscope. I could measure my circuit at work, but I think I don't want to mix business and pleasure just yet. The next step would be then aquiring a cheap oscilloscope...