We found this circuit in a 1965 Electronic Design. Transistors are still common but admit equivalents for some of them. The circuit drains a current of only 4 mA.
With good filtration, a battery charger can be used as a power source. The filter shock can be the...
This circuit, found in documentation from the 1990s, uses a common 7-segment LED display. The...
This circuit activates a recorder from the signal obtained from a telephone line in the service. It is...