The cheapest leak detector possible

Using Arduino Project Guidance
1

Hello!

This is in continuation to this thead, since I can not reply..

I have made the "sensor" by just cutting a small gap in a two wire cable such that the copper wires are exposed but not touching, see very vague drawing below:

image
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Of course my cut was not so precise. Nevertheless, it worked. I tried it by adding a drop of water on top of it, then drying it out, and it worked flawlessly. I even tried covering it with dirt, then adding water to the dirt and it again worked. Needless to say I'm very happy with the result.

I guess I should also mention my intended use - I want to install it in concrete/brick walls just below water pipes so that eventual leaks can be detected early - combined with a solenoid water valve, thousands of dollars of damage can be potentially prevented. This being said, the wire will most likely reside in some kind of sand/cement mix.

By reading the linked thread and the resources given, I also made the code alternate the signal, to supposedly prevent corrosion:


#define A 16
#define B 17

int state = 0;

void setup() {
  Serial.begin(9600);
}

void loop() {
  state = !state;

  int _A = state ? A : B;
  int _B = state ? B : A;

  pinMode(_A, OUTPUT);
  pinMode(_B, INPUT_PULLUP);

  digitalWrite(_A, LOW);

  if (!digitalRead(_B)) {
    // leak detected, perform action
  }
  
  delay(1000);
}

It is truly so simple, that I couldn't even bother adding a schematic, there's just two wires connected to pins 16 and 17 of my controller that join together as a single cable with cut slots in the insulation.

This is not really related to the question but I'm going to mention it just to spare some considerations or eventually help out anyone trying to built this as well. The cable needs to be twisted to prevent EMI and also a small capacitor can be added between the two pins - advice gotten from here.

So getting to the real question - when working on old electrical installations I've seen AC cables that have been severely corroded, which means that the AC electricity alone is not enough to prevent corrosion. I obviously need to make sure the copper does not corrode or else the "sensor" would not work. What do I need to do to make sure the copper will not corrode?

In case there's not much I can do for zero dollars to achieve my goal, I'm not very familiar with metals, so I might be wrong, but I believe aluminum is more corrosion resistant than copper. Would an alternative solution be to just use aluminum cable instead?

Thank you for your attention!

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2

Using DC will actively corrode the electrodes, but is not the only way they will corrode. There are other natural forces at work there. The electrodes will still corrode. They will corrode slower than if you used the current in the same direction every time, but they both will still corrode.

If you want a moisture sensor that will not corrode then use capacitance instead of resistance.

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3

you can just make a pcb with goldfingers, order them by e.g. jlcpcb and be happy. Even so you should not use DC for moisture, but AC. So just use 2 pins to drive the sensor with alternating polarity. When not measuring put the pins on either LOW or high impedance.

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4

To clarify a couple of things for future reference:
Starting your own topic was the right thing to do, please don't add your question to other people's topics.
If you really need to add something to a closed topic you can flag it to the moderators explaining why you want it opening and we will consider opening it for you.

5

No. Al will oxidize creating a coating of aluminum oxide which is a Very good electrical insulator.

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6

You could try to find some cold plated "material" like electronics connectors or jewellery wire. Aluminum would be the worst possible choice.

7

You say 'cheapest leak detector', I'd say 'most reliable' ( if it has to survive burried in concrete, for decades I imagine ).

8

You might want to try this out first. Concrete is very conductive for the first month or two while it is curing and in fact will be slightly conductive afterwards. Maybe you can adjust for this conductivity in your circuit.

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9

The leak detector on this HPLC sampler sitting next to me is neat. There are two through-hole style capacitors hanging down from a circtuit board. One hangs a little lower than the other. They have the same capacitance. When the lower one gets wet with any fluid conductive or not, that affects the capacitance and now the two are not balanced anymore. This sets off the alarm.

I cant imagine those two caps coat more than a few pennies.

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10

The problem would be trading reliability with cost. Gold (or gold plate) might work as it is a noble metal. I would recommend doing it with AC and only power it when actively measuring. Another approach would be to enclose it and work it as a capacitance measurement as indicated by @Delta_G .

11

This circuit does the job of measuring conductance between two electrodes.

however you will need to find suitable conductors that wont corrode simply by being embedded in concrete

12

You could take a look at this stuff:
Honeywell leak detection cacle

I have no idea how it works but it looks like it wouldn't have any problems with corrosion. It detects water alll along its length so could cover quite an area.

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13

Look up the patent number, it will give you the information. They mention it is patented but never give the number in what I found, makes me wonder what part is patented, the jacket?

14
  • Cut to 4” by 2”

IMG_3198
IMG_31981080×1080 127 KB

  • Strip 2 inches of insulation from end of two wires.

  • Insert wires in corrugated cardboard about 1 inch apart.

  • Either connect the wires to the Arduino input/GND or to a transistor amplifier then to the Arduino input.

15

The OP needs to address what happens after a leak is detected. His plan will detect a non-existent leak for months after the leak was repaired. There will a long term problem detecting a subsequent leak.

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16

I haven't found the Honeywell patent yet but there are roughly a gagillian (10^umptyump) patents on water detection that make for interesting reading.

17

Find some old wiring using multiple layers of cotton threads and they will do the detection thing just fine. I suspect Honeywell is using a porous plastic foam for insulation.

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18

If it's poured in properly made concrete wall, even several years. Concrete is waterproof if there are no cracks or defects.
Brick wall is another story.

19

Thanks to everyone for the effort and information provided!

I think choosing a metal that is as corrosion resistant as possible would be the best solution.

I've been suggested stainless steel wire, which sounds so logical I'm wondering how I didn't come up with it myself.

The problem now is that cheap stainless steel (at least that I could find) is sold as ropes and not cables (as in electrical cables), so I need to come up with some form of "perforated insulation" for it, but I guess that's a much easier task than preventing copper from oxidizing!

20

You might consider this stuff:
Sleeving

Screenshot 2024-09-05 at 1.12.56 PM
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