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.
I found this circuit in an Electronics Handbook from 1989. The circuit can be assembled with a...
The TDA2613 is the mono version of the TDA1521A and has pinouts compatible with an integrated...
This sound effect circuit uses only one integrated. We found it in a 90's EDN. The effects can be...