Based on a 555, this 80's American documentation circuit detects the voltage of a battery and can then disconnect the charger. The transistor may be a general purpose type.
This circuit from an old Argentine publication shows how it is possible to use a tunnel diode in a...
To invert the rotation of a motor by changing the levels of an Arduino output or another...
This ultra-low distortion driver was found in 80's Analog Devices documentation. The circuit has a...