Hallo Bartosz,

this circuit will not work with standard '51 micro, because standard port pin cannot deliver needed current.

Anyway, I think that it's a very nice idea to combine the rigid timing scheme of a micro with a bit 'analogous dirt' of outsourced discrete circuitry. Of course, everything could be managed by central micro, but would that be fun? If you deligate certain functions to outsourced circuitry, many hobbyists can contribute with their special ideas. Here, I totally agree with Charles.

There are many other applications, where it can be of benefit to mix micro related circuitry and discrete ones, even analogous ones. Think of a music syntheziser for instance, where the micro guarantees stable and correct tone frequencies, but where the sound is generated by 'dirt' analogous ciruitry, adding a well portion of uncertainty and imbalance, which is needed to keep the sound attractive for human ears. Such hybrid solutions can show a real amazing performance, if you take the best of both...

Kai