Room Noise Detector

One LED monitors three levels: 50, 70 & 85 dB Useful to detect too noisy environments. 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 & 85 dB. Two Op-amps provide the necessary circuit gain for sounds picked-up by a miniature electret microphone to drive a LED. With SW1 in the first position the circuit is off. Second, third and fourth positions power the circuit and set the input sensitivity threshold to 85, 70 & 50 dB respectively.
Room Noise Detector - schematic

Current drawing is <1mA with LED off and 12-15mA when the LED is steady on. * Place the small box containing the circuit in the room where you intend to measure ambient noise. * The 50 dB setting is provided to monitor the noise in the bedroom

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