Water Indicator

Are your plants thirsty? Because they cannot speak to you, use electronics to communicate with them. This simple circuit monitors the amount of water in the soil.
Or you can check whether it is raining outside without going outside and getting wet!
A simple modification shows the basis behind the so-called lie detector.

You will need these components
Resistors:
One 390 ohms (orange – white – brown)
One 100k ohms (brown – black – yellow)
Diodes:
One protection diode (1N4002 or similar)
One light emitting diode (LED)
Transistors:
One NPN type DS548 or similar small signal type
Miscellaneous:
One battery clip
4 lengths of tinned copper wire
2 x 25cm lengths of insulated hook up wire
2 x 12cm lengths spaghetti insulation
11 self-tapping screws with washers
Baseboard and project overlay No. 3