Water switch

Be careful and never use this idea working with the mains (or high voltage)!!!

Just use batteries with low voltage and the worst thing that can happen is that your battery drowns in the water...

Having made soft and paper buttons, a student wanted to have a bathing suit with LED's. When jumping into the water the LED's should light up.
Besides from the problems with electronics and water, it looked simple: two wires into the water should make a switch. The battery and LED's should be in a plastic bag and sealed.
But it didn't work!

The water, apparently being too clean, had a resistance of several K...

Solving this problem is easy and the things you can do with it are fun. Make your own rain meter, make a jacket which lights up in rain, make your milk bottle interactive etc.

Step 1 What do you need?

Tools:
soldering iron
solder
wire (preferable not too thick)
scissors
pliers
tape
(battery holder)

parts:
transistor BC457C or something like that
3V cell
a LED, around 3V
a resistor around 4K

Comments

[techxpert]

if you put a relay where the led was it could handle high voltage

[techxpert]

funny schematics what did you use i like it

[MatthewEnderle]

(removed by author or community request)

[mathieulj]

This is not quite the same circuit. The LED is at the wrong place, it should be between the transistor and the positive battery terminal(since this is an NPN transistor). Also, the symbol you used for the transistor is wrong (it's actually the symbol for a logic and gate).

The transistor doesn't make the current through the water any bigger, it simply pulls a high current through the LED when a small current goes through the water (when wired as suggested by the author).

[MatthewEnderle]

I fixed the schematic and removed the old one.

[mathieulj]

Much better indeed, although the BC457 is an NPN transistor (as opposed to the PNP symbol in your schematic). With the diode wired on the negative batter terminal, a PNP such as the BC557 should be used. If you wire the LED to the positive terminal, the NPN transistors should be used.

The essential diffrence between the two is that one ( PNP ) is controlled by the current pulled out of it while the other (NPN) is controlled by the current pushed into it.

[Jodex]

This is great if you are just learning to use transistors. And of course might be useful anyways.

Great!