Introduction: 5 Minute Water Sensor

Picture of 5 Minute Water Sensor
Something I find really annoying to do is filling up a jug of water. Because the water dispenser lets out the water quite slowly, it takes  ages to fill up the jug completely. So I came up with the idea of making a water sensor that will let me know when the jug is full, so I don't constantly have to focus on it.

Because I didn't have very much electronic experience, I made it from trash. To make it I used a cheap kid's toy that I got from a kid's magazine. Basically, it was a small sack that started laughing if you squeezed it. The sound it makes is not perfect, but it works fine. Instead of this any toy that makes a sound when a button is pressed could be used. Happy Meal toys would probably work perfectly.
The two open ended wires are just regular uninsulated 1.5mm wire. I attached it to the toy with some hot-glue (no soldering).

Making this took me just about five minutes. The rewiring was very straightforward, and thankfully there was no soldering needed.

How to make it
  1. Remove any covering or casing, so that you can get to the switch. In my case all I had to do was cut off the sack to get to the plastic casing underneath.
  2. Remove or just rewire the switch so there are two open ends. All I had to do was to press the wires onto the switch plates.
  3. Glue (or solder, depending on your toy) the wires down so there are two open wires sticking out
  4. Bend the wires around the casing, making sure that they don't touch. Leave a 1-2cm gap so it can be hung over the side of a jug.

Here's a video of the sensor in action:


CementTruck (author)2013-01-11

What would be needed for this to work in the opposite fashion? i.e. an empty pet water dish. I want an alarm to sound when the dish is empty. Maybe a float pressing up on a NC switch? I like the size and simplicity of this buzzer.

jbrecken (author)CementTruck2013-01-11

Wouldn't it zap your pet if he drank water with electricity running through it?

CementTruck (author)jbrecken2013-01-11

low power. I'm willing to take the chance. ;)

grundisimo (author)CementTruck2013-01-13

I don't know about yours, but my local dollar store sells the alarms you put on windows ( they go off when the magnet on the window is moved and the circuit breaks). I would think if you connected a wire to each side of the circuit it would do what you want... I hope I could help...

Sassah122 (author)grundisimo2013-03-02

The alarm system uses a magnet and a magnet sensor. so if you attach the sensor to the side of the bowl, at the top, and get the magnet to float, the alarm would go off as soon as the water level goes down.

sjroth (author)jbrecken2013-01-11

With a 1.5V button cell, that's unlikely

MikB (author)sjroth2013-01-12

Caution: With dogs, more likely to eat the entire device than be electrocuted!

Sassah122 (author)MikB2013-03-02

The easy solution would be to hang the device up on a wall out or reach and get some long wires do dangle down.

bajablue (author)MikB2013-01-18

lol... TRUE! ;-D

You can get float switches online; looks like this one can be set to either Normally-Open (NO) or Normally-Closed (NC):
BTW, it may be good to use a long wire and put the alarm in another room, to avoid Pavlov-ing your dog out of drinking from his bowl!

An amendment to my last comment: there are several reasons why a float switch is preferable to the two-wire method for a pet water bowl:
1- two wires with voltage between them will tend to corrode if left in water. With enough voltage (like 12V) and some salt or baking soda in the water, copper will corrode while you watch. (If you want to try it, use baking soda and not salt; electrolysis of salt water produces chlorine.)
2- pure water might not be conductive enough for some circuits.
3- depending on the voltage of the alarm circuit, your pet might feel a tingle from putting his tongue near the two wires (like putting your tongue on a 9V battery). Won't be dangerous but it might startle him. I know from experience that at 12 V in salt water, this can get quite unpleasant.

sjroth (author)CementTruck2013-01-11

I don't know much about circuits but I know that there is a way to make it the other way around. I can't remember it exactly, but I think it was a pretty basic circuit.
Of course, a float and switch would work fine. But it would probably take up quite some space in the bowl.

The Lightning Stalker (author)2013-01-13

I recommend soldering because the hot glue will eventually come loose and cause connection problems.

In some cases that may happen, but in my case the hotglue has stayed on the plastic pretty well so far.

Give it a few months. The metal will begin to oxidize even if the hot glue continues to hold.

denewf (author)2013-01-14

Good thinking!
Another great basic idea to build upon.
Some of the comments are also very helpful

jespoir (author)2013-01-14

Very cool! Keurig brewers use this same exact method, if you've ever opened one up.

gentry (author)2013-01-14

I like the minimalism of this. Since this isn't intended to be sitting in the water for long periods, this probably doesn't matter much, but try to use plain copper wire, not tinned wire, as the "tin" sometimes contains lead.

sjroth (author)gentry2013-01-14

Thanks for the tip, I'll keep that in mind for the next time I make something to do with wire.

AphexHenry (author)2013-01-13

Smart, I could use it in my cabin, when the bucket under the sink get full.

sjroth (author)AphexHenry2013-01-13

Sure, but you will probably need to add an amplifier of some sort so that it can be heard around the cabin.

AphexHenry (author)sjroth2013-01-13

No worries, if I run the water, I will be around.

Silence (author)2013-01-13

this the same principal as a moisture meter for house plants ?
I don't have much in the way of a green thumb and am always over or under watering my plants :P

sjroth (author)Silence2013-01-13

I'm sure this is very similar, but I'm guessing a plant moisture sensor would go off as soon as the soil is too dry rather than too wet. And I think it wouldn't be sensitive enough. If you need a soil moisture sensor, you can get some really cheap ones here.

xenobiologista (author)2013-01-13

Could use this in my lab. The stupid sensor on my vacuum aspirator waste trap that we use for sucking up liquids is broken.

qwerty987 (author)2013-01-12

I think you could use a similar design to make a sensor that would light up a light when the water level is low. You could use it in a motor home and you might put in several sensors at different levels so you would know about the water level but then a float might be a bit more easy.

sjroth (author)qwerty9872013-01-12

Yeah, of course you could use a toy that has LED's instead of a toy that makes a sound. But remember, originally this was only designed to get my attention while filling up a jug of water.

randofo (author)2013-01-11

You should increase the surface area by bending the wires so they interweave like zipper teeth (without touching of course). This will put them closer together, increase surface area, and generally make it more sensitive.

sjroth (author)randofo2013-01-11

Good idea. However, since the wires are pretty flexible they would make contact as soon as you touched the legs slightly. I could try it with stronger wire though.

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