This circuit that generates signals between 1.5 and 2 kHz was found in a documentation from the 90's. The capacitor C1 can be changed to obtain other frequencies.
We found this circuit in the November 1985 issue of Radio Electronics magazine. It uses TTL...
The basis of this circuit is a CA3130 operational amplifier. The transistor can be BC548, and the...
This circuit switches off a load in case of excess current acting as a fuse. The circuit is from a...