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.
This circuit, shown in the figure, can operate from 4 to 100 MHz, based on a 2N2222 transistor or...
We found this circuit in a 1988 publication. A touch of the sensor causes the relay to trip and...
This dual flasher for high brightness LEDs was found in an American documentation from the 90's....