Room Noise Detector
Circuit diagram:
This circuit is intended to signal, through a flashing LED, the overcoming of a fixed threshold in ambient noise, chosen between three fixed levels, that is, 50, 70 and 85 dB. Two operating amplifiers provide the necessary circuit gain for sounds captured by a miniature electret microphone to power an LED. With SW1 in the first position the circuit is off. The second, third and fourth positions feed the circuit and set the input sensitivity threshold to 85, 70 and 50 dB, respectively.
The current drawing is <1mA with LED off and 12-15mA when the LED is on.
Use:
• Place the small box containing the circuit in the room where the ambient noise is to be measured.
• The 50 dB setting is provided to control the noise in the bedroom at night. If the LED is on, or flashes often, then your bedroom is inadequate and too noisy to sleep.
• The 70 dB setting is for living rooms. If this level is often exceeded during the day, your apartment is quite uncomfortable.
• If the noise level is constantly higher than 85 dB, 8 hours a day, then you live in a dangerous environment.