Make an Environmental Noise Ratio Detector

This circuit is called the detector noise environment, and also indicates by means of a flashing LED when exceeding the limit specified in the environmental noise, chosen from three fixed levels. This circuit uses two operational amplifiers, in the first position SW1 circuit is not connected, positions 2, 3 and 4 define the input sensitivity threshold to 85, 70 and 50 dB, respectively.

Environmental Noise Ratio Detector Circuit Diagram:

 
Parts List:
R1 = 10K
R3 R2 = 22K
R4 = 100K
R5, R9, R10 = 56K
R6 = 5K6
R7 = 560R
R8 = 2K2
R11 = 1K
R12 = 33K
R13 = 330R
C1 = 100nF
C2 = 10μF 25V
CAP 470UF 25V C3 =
C4 = 47μF 25V
D1 = LED red
IC1 = LM358
Q1 = BC327
MIC1 = Miniature electret microphone
B1 = 9V