This circuit is from a technical documentation on the National Semiconductor LM3909. The tripping transformer has a 1:1 turn ratio and the circuit is powered with 5V.
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...