Hi again,
Good to see the idea's flowing
Just thought I'd mention that the digital LC meter project obviously isn't my design, I just built it
About capacitive sensing...'capacitive touch sensor solutions', for this app, have both advantages and disadvantages as far as I can see. The advantages are, the techniques are well documented, they explain exactly how these algorithms work, including self calibration and cancelling out constant parasitic capacitances (which will probably be higher than your actual sensor). However, perhaps I'm just worrying about nothing but aren't touch sensors purely relative? NOT absolute?
I realise the application is for a fuel tank, so its not like you want to see '32pf' on your meter, you need to convert this to real-life data, ie: how much fuel you have. But, touch sensor algorithms allow for drift in capacitances, only sensing sudden changes. They have dynamic thresholds for proximity and/or touch, which means you only really get a 'yes/no' out of them, not a nice number which is linear to the input capacitance.
That said of course, there's more then one alogrithm for measuring capacitance. Ultimately when I mentioned 'charging/discharging', all you are really doing is using the capacitance as part of an oscillator. Comparing it to a 'known' capacitance to callibrate it, and to cancel out varitions in other components (which can be damn accurate). method). It can either be purely in in software, or, if you need your micro to be doing other things, the 'CCP' module, which is on many PIC's these days.
Sorrry, I'm not trying to confuse you here, just perhaps attempting to give you more food for thought. Nothing beats experimenting
Blueteeth