I just got my first arduino about a week ago, and have some basic code running.
End result- I want 20+ proximity sensors that are sensitive enough to detect through a sheet of glass the presence of a plastic cup filled with a bit of liquid (Think beer pong table)
I've put together a makeshift capacitive sensor with a 4x4 piece of cardboard with aluminum foil on it. I've set up some code to read in the values it takes to charge/discharge, aka the capacitance (lol I THINK that's what it's called...). I've then hooked it up to an LED to vary brightness based on the closeness of an object (or the change in capacitance).
I've got all this working pretty well, and even included some code to work out smoothing it so it discards random spikes and drops in capacitance. The system works perfectly with something like a hand- turning the LED on when a hand is about 6 inches away from it and evenly increasing brightness to max by the time you are actually touching it. I've even put in editable constants for how much smoothing one wants, and average resting value and average close value, etc... (I'll upload it here when it's completely refined :P) *NOTE: This code is derived from code originally by Paul Badger(2007) that I found online. It has, however been drastically changed to fit my needs
But, that's beside the point- A cup filled with a little bit of water does NOT have the same effect on the sensor as a hand does.
Questions: A) How can I either make the sensor more sensitive so it can accurately detect the presence of a cup?/ How can I make the cup more "capacitive" (?) so the sensor can easily detect it?
B) Is there another sensor I could consider, knowing I have a rather tight budget? (However, information on the best possible sensor regardless of price might still be somewhat useful information...)
C) Is there any way I could refine the sensor EVEN FURTHER to detect the presence of a ping-pong ball in the cup as opposed to no ball?
Restrictions: A) Price B) Would like to (if possible) not require any modifications to cups/balls, as we would like them to be easily replaceable and not have to worry about their destruction C) Pressure sensors/buttons/switches/etc... are out of the question. They would require the compression of the sensor, which would require a moving part, which would require some kind of hole in the table, which would allow for spilled beer to get in between the cracks, which could mess up the electronics. (I would like to have the top be one solid sheet of glass) If I am wrong in this description, any help on that would also be appreciated :P
I think that's it! Please help me figure this out/point me in the right direction ;)