This telephone circuit was found on a 90's EDN. It keeps a flashing LED to indicate that there was a call in your absence. The components admit equivalents.
This circuit was obtained from 1967 documentation. It uses a sensor to determine the trigger...
Found in an old Popular Electronics this circuit can also be adapted to be used as a shield. In...
This one-digit TTL modulus for 7-segment display can be parto f digital projects. Many of them can be...