This circuit keeps the neon lamp on for a moment when it receives a pulse. The turn on time depends on C. The transistor is of the old type, from the 60's, when the circuit was published.
This circuit monitors the voltage of a 12 V battery. The indicated levels let you know if the...
This circuit turns on an old cassette recorder when the telephone rings, thus enabling the...
This circuit is from an old Popular Electronics, but it can be easily implemented nowadays, even...