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.
This circuit is suggested by National Semiconductor and makes use of the negative regulator LM2990...
This circuit was found in a 90s Radio Electronics. MOSFETs must have excellent heat sinks and heat and...
An oscillator slightly different from the previous one also appeared in Radio Electronics magazine in...