Oznog, thank you very much for the information! I have successfully found the sensor and read through the datasheet. The 555 circuit is as straightforward as they get, but could you tell me how you converted the frequency O/P from it, to a numerical O/P (assuming you did!!!)
I can think of several ways of achieving it, with ever increasingly large component counts! I have PIC programming knowledge, but not the kit to do any programming. So a non-PIC solution would be more appreciated, although anything would be welcome!
Thanks again.