Capacitane switch

[mixos]

Take a look at the project I attach you:

Wireless Liquid Level Sensing for Restaurant Applications

It measures capacitance to determinate the liquid level of a glass and send the results wireless on a base station. It's quite interesting and i think you can take much ideas on how to convert it to fit your needs.

Hope this turn you to the right direciton.

[bogdan]

why not use ultrasonics?
put a senstor at the top of the tank and it can determine the distance between the sensor and the water.
or, i am thinking of another way, with the capaciatance switch. maybe a better rensor would be to run 2 insulated paralel, horizonatal wires in the tank. put them very close together. water cobing between them means an increase in capacitance.
i am thinkting of another basic method.
use a magnet attached to a floating device, and enable the floating device to moove up/down on a vertical wire at the edge of the tanks. on the other side of the tank you could have some reed switches.

[bogdan]

here is something nice...........
http://www.newscientist.com/news/news.jsp?id=ns99992123

[Kid_TanECE]

 

Looking at the circuits that converts pulse width to voltage. I found that it might be very tasking to implement the circuit as well as finding the neccessary parts. Some devices are not readily available as there are not a lot of experimenters from where I come from.
 Looking at the catalog of one of our electronics stores, I found that they have an available frequency to voltage IC named the LM2907N.
I wonder if it would be feasible If I could connect oscillator output directly to this device so I could use its output to drive my ADC and display?
By the way, I changed my capacitance tank design. Instead of making the sides of the tank the conducting plates, I plan to place two copper plates wrapped in insulation(I plan to use two PCBs for my prototype),  and place them inside the tank at a few centimeters from each other. I'm thinking I could get a more accurate capacitance with this design.
What do you guys think?

[bogdan]

i have a suggestion.
putting the plates closer togther increases the capcity, wich is small when using water as dielectric.
also, i suggest that when insulating the plates, use something wich has a high relative permitivity. this means that you will have a big difference between the 2 capacitances.
why not use thick insulated wire from a transformer?

[Staigen]

Hey Smaug, something come to my mind when i first see this topic, why not use an emittercoupled clapp-oscillator with a frequency around 200 to 600 Khz or so, with a capacitive sensor as part of the tuning capacitor, and using a 4046 ic to detect when the saltwater is reaching the sensor. I can upload a little schematic for you to show what i mean, if you want to. Btw, what is your tank made of?

//Staigen