Found in a Popular Electronics from the 90s, this circuit activates a recorder for automatic recording of telephone calls. The circuit was used with old cassette recorders of the time.
The figure shows three circuits for using headphones in amplifiers with speakers that do not have...
In this charger, the charging current is basically limited by the LEDs. The transformer is a low...
This configuration is from an old integrated circuit manual. The circuit can be applied to modern...