Best choice for detecting water?

[ardhuru]

- Using and ADC channel to read the resistance across the probes. Normal state should be infinite resistance; anything less and sound the alarm. However, I don't know how to use ADC to measure resistance. According to the datasheet, the max recommended impedance 10k for ADC is anyhow. So I don't know if this is a poor idea besides the point.

You could use the ADC input, or use the input as a digital pin. Essentially, the resistor between the pin and ground, and the water body would form a potential divider. With no water, your ADC reading would be almost, or equal to zero. When water bridges the probe, it should get close to the full Vdd (200+, for the resistor value I have used).

Alternately, if you're using the pin as a digital input, it would be low till water bridges the probe, and then swing high.

The 2nd version of the schematic would be even better, where you control current going thru' the water, as you could reduce the corrosion by a very significant amount.

BTW, please excuse the shabby drawing, thought it would be faster than drafting it.

Regards,

Anand

[Acetronics2]

Hi,

I think a fair solution could be to use capacitive detection using the RC oscillator :

The probe being the ... Capacitor.

just compare the duration of, say 256 osc periods to an external RCTime result ...

With water , the capacity of the probe is high ... Osc runs slow ...

When dry, the capacity is low and osc runs faster ...


Interest ??? can even run the 32 Khz clock for power saving, no direct contact of the electrodes and the water ( works with " pure" water also - no corrosion or dirt disturbing measurements )

Some level MEASURES can also be made using the RCTime command, but less power savings ...

Alain

[ShortBus]

Anand,

Thank you for taking the time to sketch out your schematics! It's a big help.


Alain,

I'd have no idea how to implement something like that (I'm a software guy who's muddling through electronics); though it does sound interesting.

[Charles Linquis]

About 40 years ago, I needed electrodes for electrolyzing water. All the metal ones had problems, but I found a great solution in the carbon rods that go down the middle of zinc-carbon dry cell batteries. They even have a metal cap crimped on one end that you can solder to.

If you can still find them.

[ardhuru]

You should be fine with stainless bolts as sensors, as long as you've properly insulated / epoxied the connection between them and the wire. Plus, if you can, run the pic off a 3 volts supply, the probes will last that much longer.

Regards,

Anand

[Melanie]

This device is extremely reliable (as long as it's not sewage which tends to coat the optics!) and is actually manufactured by Honeywell Microswitch in the USA. Connect with minimal components directly to your PIC (or even Relay).

http://docs-europe.electrocomponents...6b8001adaf.pdf

It is a little power-hungry for Battery applications though.

You don't have to go Stainless Steel if you use AC exitation on your probes... PWM say a 1kHz signal to one probe (via a 100nF Capacitor, the other probe (again via a 100nF) can be used to detect the signal returning. To minimise power consumption, turn the PIC on only every few seconds (typical Rain Detector application to alert you to take the washing indoors).

[Acetronics2]

Hi, Folks

This one doesn't show any Pic ... is not a " Bling-Bling" device, but works perfectly ...

Published in ... 1983 !!!

DUS means: general use Silicon diode : 1N4148, BAW62 ...

Alain