This electronic circuit is a simple water level indicator alarm that is based on few transistors . The circuit is very simple and it has a very low current consumption , so you can use a 9 volts battery to powering this water level indicator alarm . This water level indicator alarm electronic circuit can be used even for rain alarm or short circuit alarm , a resistance with a value from 0 to about 1 M ohm will trigger it . The Q1 transistor acts as a switch which applies current to the unijunction relaxation oscillator Q2 . The signal frequency of the alarm circuit is give by the values and ratios of the C1 / R2 .
If you don’t have the transistors marked on the schematic diagram you can replace them almost with any similar types . As you can see in the schematic diagram , between probes is mounted a switch ( you can use a push-button) for testing the circuit , but it can be removed .
The speaker used in this project must have a impedance between 15 and 90 ohms .