Hi Steve,

yes I already read the patent notice. But for educational purpose explanation would be appropriate.

From your message it looks like you technique would be different from this Optical PLL.

I have tried to put this PLL on paper but couldn't get the oscilation.

Keeping modulation freq. and the distance fixed then every time the inverted echo interfers with the modulation, it will cause one condition all the time same. How it is going to oscilate ?? that I didn't understand.

Of course the oscilation can be used with 8052 to measure the distance.

Simon