The sensors of this liquid alarm are formed by two pieces of wire with the ends peeled off. The relay depends on the supply voltage that can be between 3 and 12 V. The transistors can also be the BC548.
Based on components from Linear Technology, we find this circuit in a 2005 manual. The circuit...
This circuit triggers oscillator 555 when the supply voltage drops below the value set in the pot....
This amplifier provides a power near to 1W. The supply must be made with a voltage of 9 V coming...