This circuit that draws 1 out of 8 LEDs was found in an 80's American documentation. The circuit can also work with an astable using the 555 instead of the 4046 which is not a common component today.
This circuit using an operational amplifier was found in old American documentation. It can be...
If the circuit oscillates, emitting sound, it is because the transistor is good. This simple...
Like the previous circuit, this is used in the analog part of the telephone lines. The same...