Decibel circuit and structure schematic
As shown in the figure is a decibel circuit that responds to sounds from a pressure level of about 60 to 70 decibels. The sound picks up the 8 ohm speaker by a transistor and an LM324 stage op amp amplification section. You can also use a dynamic microphone, but I find it more sensitive to speaking. The four op amp sections of the remaining 3LM324 are used as LED indicators for the voltage comparator and driver 3 or incandescent lamps spaced about 3 dB apart. Another transistor is required, with the incandescent down light displayed. A 12 volt, 50 mA lamp can be used. Each indicator light represents a volume change of approximately 3 decibels, such that when all 3 lights are turned on, the volume is approximately 4 times higher than the level required for a light. Adjustable sensitivity with a 500K pot, such a light comes with a reference sound level. The other two lights will show an increase of approximately 2 and 4 times.
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