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