Picture of bathtub water level detector
I have always thought that someone should make a product that will sound an alarm if your tub is in danger of overflowing..

So, I have pieced this one together out of two easily available items that can be found very inexpensively at the Dollar Tree or ebay

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Step 1: Things to get

Picture of things to get
touch activated light up flashing led toy. 

I found this little frog at Dollar Tree, but you can also find them on ebay,
for example: 
ebay: touch activated color changing led light up toy
ebay: water activated color changing toys

Magnet activated security alarm siren, from Dollar Tree

Suction cup to hold the frog to the side of the bathtub at the desired water level

Hot knife/soldering iron
some lengths of thin wire

sugru to reseal the frog after modifications are made

Step 2: Reverse engineering

Picture of reverse engineering
I spent some time looking at the two circuits and redrawing them so I could understand the a bit better.

I always seem to want to combine two electronic products into one, but I'm never sure how to handle the fact that each has its own separate power supply and how to connect them in such a way that the power supply of one does not defeat/destroy the logic of the other.

I found by poking around that the power supply of the shrieker was interfering too much with the behavior of the frog circuit, so I shorted that out and relied entirely on the frog circuit power supply.  This wound up making the shrieker less loud, but still audible, so I went with that.

Step 3: Combined schematic

Picture of combined schematic
I poked around till I found an arrangement that worked.

Siren circuit:

I shorted the reed switch as shown.

I removed the power supply and created connections to the frog circuit there.

Frog circuit

Soldered in the leads from the screamer circuit from one pad on the high side of the led and the other lead to ground as shown.

Step 4: Reassemble the frog and siren

Picture of reassemble the frog and siren
The reassembled frog needs to be water tight.  Also, I need some way to run the wires from the frog circuit to the screamer circuit, so I added some eyebrow/antennas to him.

foobear (author) 2 years ago
Interestingly, this guy published a similar idea the very next day, though his design is better for sure: http://kipkay.com/featured/liquid-alarm-gadget/
omnibot3 years ago
Very cute and practical.
In step 2 the capacitor is actually an inductor (fancy name for a coil).
ChrysN3 years ago
Smart idea and I really like how you used a frog, that's cute.