The voltages in an adjusted range in the trimpots are indicated by 3 LEDs. The LEDs indicate when the voltage is below the range, above the range and in the range.
This filter, from an audio publication from 1977, passes the frequency range corresponding to the...
In the figure we have three voltage doubler configurations that can be used in high and low...
This circuit was found in Motorola documentation from 1966. The lamps are according to power and...