Water Alarm - Maker Factory ELECTRONICS EXPERIMENTS BOX Manual

2.67 Water alarm

Circuit 142: Water level alarm with LED
Setup information
Install the two transistors, the diode and the four resistors as shown in Fig. 2.142. The ten jumper wires
come next. Check the placement on the board again and only then connect the battery.
Experiment
Even if everything is wired correctly, nothing will happen at first. But if you dip the two bare wire ends that
represent the sensor in water, the red LED will go on. You could use the circuit to monitor the water level of
the rain barrel in your garden.
The circuit diagram for this experiment is shown in Chap. 3, Fig. 3.142.
168
Components required:
2 x 2N3904 transistors,
1 x red LED, 1 x 1 kΩ
resistor, 1 x 10 kΩ resis-
tor, 2 x 220 kΩ resistors,
1 x breadboard, 1 x 9V bat-
tery with clip connector
Fig. 2.142: Water level alarm
with LED