Found in a 1924 book by Gernsback, this circuit uses a double variable capacitor, a component not very common at the time. Listening was done on a loudspeaker at the time.
This circuit triggers a relay when a pulse of light hits the LDR. The potentiometer serves as a...
In the figure we have the way to implement a NO OR or NOR gate with an operational amplifier. The...
The presented circuit is used to test ordinary fluorescent lamps. This circuit also has a mains...