The LM3914 is a monolithic integrated circuit that senses analog voltage levels and drives 10 LEDs, providing a linear analog display. A single pin changes the display from a moving dot to a bar graph. Current drive to the LEDs is regulated and programmable, eliminating the need for resistors. This feature is one that allows operation of the whole system from less than 3V.
www.ti.com/lit/ds/symlink/lm3914.pdf
www.ti.com/lit/ds/symlink/lm3914.pdf