This circuit allows the activation of a remote telephone bell made with a common piezoelectric capsule. The circuit does not need power, as it is powered by the line call signal itself.
The inverter circuit shown in the figure can be used to power a fluorescent lamp in an emergency...
This circuit was found in 80's Popular Electronics. The circuit uses an infrared-sensitive phototransistor...
Found in documentation from the 1980s, this circuit generates signals that can reach a few...