Designing a low-voltage Moisture Sensor Grid or Pad?

[Firstly, my apologies to alt.engineering.electrical if this post is out of place there.]
Any ideas (and/or recommended references) as to where/how to get started?
What I'm aiming to create is a floor pad, the size of a prototype to be about four square feet, equipped with densely spaced, evenly distributed moisture-detection points. Obviously the use here of many moisture sensitive microchips would get too expensive. So I'm thinking more along the lines of a grid pattern of wires: wire anodes criss-crossing wire cathodes, each kept vertically separated by some non-compressible material possessing excellent water absorbtion characteristics; such that a low voltage current will flow between anode and cathode (to trigger an ultrasonic-alarm device) whenever "Kitten decides to do her thing" and the material thereby becomes wet... Now, I don't happen to know of any specific materials that would fit this bill. Nor do I have the specific technical experience or knowledge to guesstimate whether this idea is even plausible or not.
What I do know I have this problem with 'people and their pets' inside the house. I have poured over the internet searching for possible technical solutions to apply to this problem. Some I've purchased and tried (e.g. cat facial pheromone or Feliway), but none have worked. I have researched electronic pet repellants and found a couple of such products that do have a proven track record. But these simply deter animals from entering or remaining in a certain area by emitting an ultrasonic noise (silent to humans) upon the detection of motion --any motion, by any pet, person, or thing, for any reason. Such a device would definitely scare the cat out of the house, but wouldn't meet with the cat's owner's approval since it is not selective for specific problem behavior, and she wants the cat living indoors. Thus I need to develop a customized (yet affordable) technical solution, such as would briefly emit an ultrasonic "noise" to startle the cat, but *only in response to wetting behavior* by the cat.
Therefore, helpful feedback/references/possible plans/schematics/suggestions appreciated?
TIA, Ken
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Ken Moiarty wrote:

You don't need anything that complicated. Just get a suitable non conductive substrate and use contact adhesive to cover it with a single sheet of aluminium foil. Then remove small strips of foil to leave an interlocking pair of spaced fingers. Or form the same sort of thing using conductive ink. Or use a soft pencil and then electroplate.
Now energise it with a low current alternating voltage between each set of fingers and sense the impedance. When there is a step change, stick a couple of thousand volts, very limited current across it - or sound your ultrasonic "noise". Use ac for sensing to minimise corrosion.
With different settings, it can educate, terminally educate if you wish, rats,etc. They need quite a large current before they catch fire, btw and it ruins the fingers.
With yet more different settings, it can play a reward "happy tune", when fitted to a kiddie's pottie and activated by No 1s or 2s.
Mixing the rat and the child application could be unfortunate..
--

Sue













Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

of
one or more stock unetched PC boards. use dremmel or etching tool to cut traces. Darlington transistor or op-amp to sense conductivity.
equipped with densely spaced, evenly distributed

densely spaced is not needed.
note: urine is hard on electronics. you should seen the mess mice make of things when they get inside.
maybe trigger a self cleaning spray?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

relay switch | | E1--0 sensor 0-----------(+) 0---/ ----0 | Op Amp (out) ------relay coil--- ---------|------------(-) | | | Gnd R1 R2 | | gnd gnd
A simple Op Amp comparator circuit driving a relay would do it for you. There needs to be only very little current to get the op amp to go high at the output. I like the aluminum foil fingers idea that was posted. It is cheap and easily replaces after the critter soils it.
I don't know what the resistance of cat piss is but it will help you determine what value resistors are needed.. R1 and R1 should be equal. I am guess a 12V source and 100Meg resistors to start off with.. Look for a relay with a high coil resistance, They do make some "reed" relays that take very little current to fire..
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Fri, 26 Aug 2005 15:33:19 -0500, "DBLEXPOSURE"

LOL, you are a troo loon!
Here's what he needs:
+6V>--+----------+---------+--------+-----------+ | | | | | | | | [10K] | | | | | | [SENSOR] | +---|--[1M]--+ | | | | | | | | [10K]<--+--|+\ | E | |POT | >------+--[600R]--B 2N4403 VIN>--+-------------------|-/ LM393 C | | | | +--------NO | | | +-----+ | [100K] | | |K | O--> |<--NC | | | [DIODE] [COIL]- -| | | | | | O--COM GND>--+----------+---------+--------------+-----+
Ground the unused inputs and output of the unused comparator, then to set it up what you do is to run the pot all the way to ground, attach the sensor and pee on it, and then adjust the pot until the relay clicks in and then just a little bit more for good measure.
Then, you take the sensor out wash and dry it and put it back. The relay can be used to trigger any "disciplinary" device, remembering that Mark Twain said about cats, "Of all God's creatures, there is only one that cannot be made the slave of the lash. That one is the cat. If man could be crossed with a cat it would improve man but it would deteriorate the cat."
--
John Fields
Professional Circuit Designer
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Lol, Can't argue with that..
But I did build this some years ago,(Not to monitor cat piss). 2 resitors, op amp and I belive the relay was 5V with a 500ohm coil. Worked fine. Light goes on, Light goes off.....
But I am sure you will tell my why it dosen't work...
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
DBLEXPOSURE wrote:

Personally, I wouldn't use either of them! Sorry about that.
Yours because your comparator is using ground as the reference. Any "leakage" across the sensor is going to trip it. The cat stepping on it, or even breathing on it, probably would. For a non-perfect op amp, it is highly likely that it will be permanently tripped due to offset voltage. Because you don't control the back emf from the relay when it switches off - which could easily zap the op amp. Because you don't control the maximum voltage between the inverting and non inverting inputs, which could easily cause the op amp to permanently lock or self destruct. Because you use dc across the sensor, which will lead to corrosion and premature failure. Because you have no sensitivity or trigger point or hysteresis adjustment. Those sort of things. Depending on the sensor and the op amp, it certainly could work - but the odds are that it wouldn't work reliably in this application..
-- Sue
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Sat, 27 Aug 2005 09:58:42 +0100, Palindr?me

--
And mine?

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
John Fields wrote:

Oh, every engineer has their own way of doing things, have their favourite chips and favourite building blocks.
I am quite possibly too hung up on always using ac with liquid sensors. I thought that your circuit, even with the current limited to microamps, would tend to encourage dendritic growth or electrochemical migration - particularly with the odd chemicals that might crystalise out of cat urine in place. It depends on the gap left between the fingers and the underlying substrate, of course. But you do have 6 volts across the gaps.
I may easily be wrong! I tend to be very lazy and stick to the building blocks I have used before..
--
Sue
















Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Well, to be more precise, it's not *literally* a kitten that's doing the urinating here, but rather two full grown cats. (The long story is...)

My intention is to modify (or replicate) the decor mats currently being used to protect the carpet in our hallway, such as to _stealthily_ incorporate the moisture-sensor mat. This will be not only for the learning needs of the offending cats, but also to minimize the likelihood that a certain human might otherwise object to the 'operation' without giving it time to reach success. For as most do-it-yourself 'engineering' goes in my experience, anticipate plenty of trial-and-error based refining and tweaking before it performs "in the real world" for me as conceived.
Ken
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Fri, 26 Aug 2005 17:44:44 -0500, "DBLEXPOSURE"

--
If it did, you were just lucky.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I used it in an old Ikagami studio camera. We had a rash of Plumbicon tubes that has short lived filiments. I used the circuit to insert a light bulb in the filiment circuit when the camera was put into standby mode to cut the filiment current when the camera was not in use.
Could not have been luck because I don't have much of that...
Just a looney hack, I guess...
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Had you thought of buying or hiring the bell and pad system used for kids that wet their bed?
David
Ken Moiarty wrote:

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Yes. But I couldn't find any such products for kids that uses a pad which covers any appreciably sized area. A google search listed product after product in which the sensor "pad" is no more than a few square inches; just enough to fit in the diaper. Of course, I didn't check out everyone of the thousand or so Google search results so... If you know of such a product which employs a sensor pad that actually employs some spread-out like surface area, I would be eager to know the name of it.
TIA, Ken
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Fri, 26 Aug 2005 13:11:39 +0000, Ken Moiarty wrote:
Such a device would definitely scare the cat out of

So, finally, it comes to light that this is some babe, and she insists on bringing "her" cat into your house if you want to get laid?
It ain't worth it. She's addicted to cat, and can never love a man. Lose the bitch.
--
Flap!
The Pig Bladder from Uranus, still waiting for that
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Pig Bladder wrote:

That's life, if you want pussy, you have to have a cat...
--
Sue

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Thank you for this earnest piece of advice.
Ken :)
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here. All logos and trade names are the property of their respective owners.