How to make a simple and cheap liquid switch (without floats).

Step 1: What you need:

Picture of What you need:
There are a few simple and accessible items that you will need to make this switch.
- 1 NPN Transistor - I used the TIP120 from radioshack but just about any NPN will do.
- 1 1Kohm resistor
- 1 capacitor - I used a 25v 1000 microfarad. The capacitor is not necessary but it will allow for a slight delay so a pump will stay on for a bit longer when the liquid is no longer contacting the electrodes.
- A piece of copper or other heat sink. If you are using this for high current operation you will need a bigger heat sink than just a piece of copper.
- misc wire - I'm sure you have some laying around.

Note: For this switch to work the liquid will need to be slightly conductive. It works with tap and purified water but probably not distilled unless an electrolyte is added.
Remove these adsRemove these ads by Signing Up