VU meter circuit is an IC number LM3914. This is a circuit that is commonly used standards. Within the integrated circuit LM3914 is a voltage range advantage. This is the fourth leg split. Reference voltage pin 6 is low, and the reference voltage divided up.
When raising the power supply circuit and the signal came, the sound signal to be via D1 Optical Direct Fire only split the signal to positive The C1 and R1 signal smoothing filter. Then, light is sent through R2 to access the input pin 5 of IC by the IC to the display of the signal starts from the output pin 1 or LED1 contiguous to the leg 10 or LED10. You can choose form of a display 2. is a bar display and the display. Select use the switch S1. VR1 which acts on the set voltage reference ICs and R3 of the output current limiting function. If the value at which R3 LED1-LED10 are very bright.