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 common unijunction transistors, this 1968 General Electric circuit is powered by 12 V. |...
The transistors can be the BC548 and BC558 and the operational can be a 741. The circuit is from...
We found these circuits in a Popular Electronics from the 90s. The circuit has a simple low power...