This simple circuit makes use of neon lamps to indicate the voltage of a power grid. The lamps are common neon and the circuit indicates whether the voltage is 110 V or 220 V.
This integrated circuit is recommended as a standard amplifier in sound equipment, TV sets,...
This circuit was taken from a popular 90's Electronics. The LDR is mounted next to the LED to feed...
This circuit with the operational amplifier CA3130 was found in an English publication from 1977....