The circuit Bargraph Voltage Indicator used IC op-amp two quad voltage comparators to illuminate a series of 4 LEDs indicating volume level.
The op-amp used in this particular circuit is the LM339. It is a popular IC and should be available from many parts stores.
The 1K resistors in the circuit are essential so that the LED’s turn on at different Voltage input levels.
The sensitivity can be decreased with R1 and the input control to read higher levels.
This circuit is easily expandable with more op-amps, and is not limited to use with the LM339.
Detail more,Plaese read in image.