Room Noise Detector

This circuit is intended to signal, through a flashing LED, the exceeding of a fixed threshold in room noise, chosen from three fixed levels, namely 50, 70 and 85 dB. Two Op-amps provide the necessary circuit gain for sounds picked up by a miniature electret microphone to drive a LED.

Parts:
R1____________10K 1/4W Resistor:
R2,R3_________22K 1/4W Resistors:
R4___________100K 1/4W Resistor:
R5,R9,R10_____56K 1/4W Resistors:
R6_____________5K6 1/4W Resistor:
R7___________560R 1/4W Resistor:
R8_____________2K2 1/4W Resistor:
R11____________1K 1/4W Resistor:
R12___________33K 1/4W Resistor:
R13__________330R 1/4W Resistor:
C1___________100nF 63V Polyester Capacitor:
C2____________10µF 25V Electrolytic Capacitor:
C3___________470µF 25V Electrolytic Capacitor.