AC voltmeter circuit composed of milliammeter

By adding a few semiconductor diodes to the milliamp meter , you can measure AC voltage and turn it into an AC voltmeter , as shown in the figure VD1 and VD2 form a half-wave rectifier. The four resistors in the figure are separate multiplication resistors: the multiplication resistors in figure b are connected in series, and their effect is the same as that in figure a. The " * " terminal in the figure is the common terminal. No matter what voltage is measured, one of the two test leads must be connected to the " * " terminal .