This circuit is for traditional old-style telephone lines found in an American 1980s documentation. Components are common and the optical coupler can be replaced with an equivalent.
This circuit found in a 1988 documentation consists of a timer or sequential timer controller. The...
XTAL from 4 to 20 MHz can be used in this oscillator. The XRF choke can range from 10 to 100 µH...
We find this simple musical instrument in a 1977 Radio Shack documentation. The key resistors must be...