leak detector

Add some salt and see what happens.

Pure water does not conduct. Impurities in the water can cause conduction. Try salt , like the previous poster suggested!!!

Ionic liquids are poor conductors, and, depending on the electrodes, may not conduct at all at low voltages--you have to overcome the cell potential before you can get any current to flow.

One approach would be to use a 2N7000 with a 1-10M resistor from gate to source. Connect the sensing gap between gate and the + battery terminal, and connect the FET in series with the alarm negative lead--drain to the alarm, source to the - battery terminal.

Adding 0.1 uF in parallel with the resistor will give you decent static discharge protection.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal
ElectroOptical Innovations
55 Orchard Rd
Briarcliff Manor NY 10510
845-480-2058
hobbs at electrooptical dot net
http://electrooptical.net

And with the right amount, you can make chlorine too, good for swimming pool.

Using a couple of AMPs,

N\aCl + HOH -> NaOH + H + O + Cl

On a sunny day (Wed, 25 Aug 2010 07:48:25 -0700 (PDT)) it happened linnix wrote in :

Especially the H and O, form an explosive gas. One teacher I had used electrolysis that way to blow soap bubbles, that then floated in the auditorium. You could explode those with a lighter, He also mentioned the volume goes up faster then the diameter of the bubbles, so the bang goes up exponential with size.

les,

Yes, a H & O motor can drive the filtering pump as well, with waste HOH back into the pool.

To reiterate what's been said:

• Absolutely pure water isn't all that good of a conductor. In fact, you can cool vacuum tubes with 1000V plate potentials using distilled water from the store, and flow only a few milliamps of current to ground when the coolant water is fresh. (I haven't done this, but it's in the Amateur Radio literature).

• Even with a bit of salt in it, water doesn't conduct anything like a metal does. Some experimentation with an ohm meter, some water, some salt, and some lemon juice would be educational at this point.

• So you can make a leak detector that 'looks' for tens or hundreds of k-ohms across your leads, and hope that the water has enough impurities to conduct. It's been done before.

And the meta-lesson:

• There's a reason for the saying "thems what can, do; thems what can't, teach". Not everything you learned in high-school electronics was right. In fact, not everything you learn in _any_ class is 100% right; it's just that some classes manage to teach more right stuff than others.

• So take everything you hear (even this posting from me!) with a grain of salt. Learn how to check your assumptions (which means you have to learn how to _recognize_ your assumptions) before you do anything really critical.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at http://www.wescottdesign.com/actfes/actfes.html

An oft repeated lie ;-)

Common copper electrodes corrode making yellow/brown to green/blue gunk.

An inert anode (graphite, lead dioxide, platinum) will make hypochlorite (bleach) and chlorate, but not more than traces of chlorine gas.

Acid is required to liberate chlorine, or a divided cell (which makes its own acid).

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms

Well, 18Mohm comes to mind. I can think of a few people here who consider that a conductor.

I don't remember what units, it's always "megs", missing the dimension. Possibly cm.

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms

Hypochlorite or Chlorate can work too, if I can transfer them to the pool water without transferring the salt.

--
_Pure_ water (distilled, deionized) is a non-conductor, but ordinary
tap water isn't.  

It isn't usually a _good_ conductor, either, so what you could do
would be to increase the voltage across the probes and measure the
current through them.  Then:

         E
    R = ---
         I

will get you the resistance.


Try this: (View in Courier)

            It-->       
     +----------------+------+--E1
     |+               |+     |
    [9V]           [METER]  [E2]
     |   ->|   |

--
Correction:

Using a potentiometer to measure the voltage across R2 would cause no
loading whatsoever once null was achieved.

here is a guide that uses a smoke detector

ep2/Finish/

apparently the sensing circuit has a high enough potential to overcome the water resistance?

it would be nice if it would detect pure water..since we may be doing the rain barrel thing in the future water shortages to come.

i wonder would these inexpensive models detect pure water?

=A0|

=A0|

=A0|

If that's what you wanted to do -- use some other property of water. One example is its high permittivity - it makes for a great change in capacitance. All the better in that the electrodes can be sealed in a thin dielectric, protecting them against the corrosion likely in a resistance measuring system. Yes, its more complicated - if you don't want to do some real studying/learning, you may want to get a commercial device.

water?

Many years ago I did such a sensor for irrigation monitoring...

PVC pipe, capped on the end, copper pipe interference-fit inside, cage outside ("ground").

IIRC, a few hundred pf's per foot of water. ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |

                   Spice is like a sports car... 
     Performance only as good as the person behind the wheel.

i tried the smoke detector mod. it would not detect the water. the deivce is more sensitive to touch of my skin than the capful of water.

On a sunny day (Wed, 25 Aug 2010 09:54:00 -0700 (PDT)) it happened divx dude wrote in :

Some water detectors use a mercury contact in a floating case. When water level rises, the thing tilts a bit, and the contact makes. I have a pump in the basement with such a thing attached, to automatically start the pump if the basement floods (happened once). I also have an electronic alarm, that works very much the way Phil described, except I use a PCF8591 ADC and 1M to plus (so +5V) with 2 long galvanised screws as sensor, one connected to ground and one on the ADC input. When water reaches the screws, the ADC voltage drops below 5V. Works on the water here. You could use a normal HC74XX gate, maybe one with a Schmitt trigger input, too.

+5 | 1 M | 0---- 1 M ------- HC74xx | sensor 10 n pins | 0----------------------

On a sunny day (Wed, 25 Aug 2010 17:46:03 GMT) it happened Jan Panteltje wrote in :

Oops:

+5 | 1 M | 0------- 1 M ------- HC74xx | sensor 10 n pins | 0----------------------

Yeah I just stuck my DMM probes in a glass of tap water. 30k ohms or so. Funny I thought that the conductivity was a lot lower than this. Many years ago I tried measuring the conductivity of the water in my fish tank. I had hard time.... I wonder what I did wrong?

George H.

I recall some nice videos of 'pure' water being attracted to a high voltage probe.

d text -