PIC water sensor

[The Master]

Hi, How would i go about detecting water with a PIC?

I remember as a kid i made a little water sensor that turned an LED on. I think it used 2 transistors as a darlington pair but i cant find the book i got the circuit from. What about having pulldown resistors to make sure the PIC wont get a signal when there is no water.

Am i overcomplicating things again? It would be nice if i could have a high value pulldown resistor and just put the wires straight in the water but i would need a higher value resistor than the water and im not sure if that would be enough for a reliable pulldown

[skimask]

Built a level sensor for a friend's aquarium a couple of years ago. Took a small plastic ball (say 1/2 red, 1/2 white for arguments sake), weighted down 1/2 a bit so that end would stay in down in water, put a small piece of tin foil on the top end, then hung a small chunk of copper over the side, under 'tension'. I used the ball so the 'electrical bits' wouldn't get submerged and mess with his fish. Water level would drop, alarm would sound when the connection was broken. Since I was using a PIC, I set it up so it would only check once every minute or so instead of a continuous current flow. Once the alarm was tripped, then it would go continuously.

Or you could treat the water as the dielectric of a capacitor or a variable resistor, put 2 'probes' in there and use ADCIN or POT to check the resistance/voltage across the probes, looking for a major change.

Or a float and a lever switch, or an IR LED/detector pair, or, or, or, or...

A thousand different ways of doing it...

[Archangel]

. . . or put a magnet on that little ball and use a reed switch or hall effect device . . . How much water are we talking about here? A puddle under the water heater, a sump pump , a fish tank . . . ?

[Normnet]

The Quantum touch sensors are very good at detecting water.
The human body is 9x% H2o.
These sensors can also detect through non metallic containers.

Norm

[The Master]

How much water are we talking about here? A puddle under the water heater, a sump pump , a fish tank . . . ?

I hope your ready for this one. I need 2 sensors. One to go in a skull and one to go in a coffin.

Now before anyone starts making assumptions about me let me explain that these are halloween props that have misters in. They are going outside and will run for a few hours but they use water pretty quick. Ive got valves etc all ready to top them up but i need to know when they go below a certain level. To make it simple im only having the 1 sensor. Instead of a high level sensor im just going to turn the valve on for a set amount of time.

I am i bit short on space so i was thinking of 2 wires dipped in the water. I like some of the other ideas. I never thought about doing them before. I do want to keep the cost down though. Things like "Quantum touch sensors" sound expensive.

One other thing i should mention. The PIC thats controlling it will be controlling a lot of other things aswell. I cant use any blocking commands. Ive never used ADCIN or POT before so im not sure if they are or not

[mackrackit]

Use the wires and a 741 op amp.

When the water conducts across the wires the op amp triggers with the out put of the amp going high going to the pic. Or low if you wire the op amp the other way.

[The Master]

Sounds good. Ive found an "LM741 SINGLE OP AMP DIL-8 (NSC) RC" in rapid. Ive not done much with opamps before but i found a page on google about the 741 so i can start learning now.

Thanx for your help