This circuit of measurement of level uses the UAA180 of SIEMENS and a circuit of rectification of precision, round the IC2B. The calibration has become in steps 3db from the one Led in the other, ensuring, a very good rate of precision, in the measurement of entering acoustic signals. The Led can be square, thus when they are placed the one by in the other, they give the picture of bar, without space.
R1= 47Kohm R7=2.2K ohm D1....8= LED GREEN
R2= 1Mohm R8-10=330Kohm D9-10= LED YELLOW
R3= 33Kohm R11=180Kohm D11-12= LED RED
R4= 10Kohm C1= 47uF 25V D13....17= 1N4148
R5= 220ohm C2-4=47nF 100V IC1= UAA180
R6-9=390ohm C3=2.2uF 25V IC2= TL072
All the Resistors is 1/4W 1% metal film