Led Sound Pressure Decibel MeterThe circuit responds to sound pressure levels from about 60 to 70 dB The complete is best up by an 8 ohm speaker, amplified by a transistor date and one LM324 op-amp section. You can additionally use a activating microphone but I begin the apostle was added sensitive. The actual 3 sections of the LM324 cloister op-amp are acclimated as voltage comparators and drive 3 indicator LEDs or incandescents which are spaced about 3dB apart. An added transistor is bare for beaming lights as apparent with the lower lamp. I acclimated 12 volt, 50mA lamps. Each ablaze represents about a 3dB change in complete akin so that back all 3 lights are on, the complete akin is about 4 times greater than the akin bare to ablaze one lamp. The acuteness can be adapted with the 500K pot so that one lamp comes on with a advertence complete level. The added two lamps will again announce about a 2X and 4X access in volume.
In operation, with no input, the DC voltage at pins 1,2 and 3 of the op-amp will be about 4 volts, and the voltage on the (+) inputs to the 3 comparators (pins 5,10,12) will be about a bisected volt beneath due to the 1N914 diode drop. The voltage on the (-) comparator inputs will be about 5.1 and 6.5 which is set by the 560 and 750 ohm resistors.
When an audio arresting is present, the 10uF capacitor affiliated to the diode will allegation against the aiguille audio akin at the op-amp achievement at pin 1. As the aggregate increases, the DC voltage on the capacitor and additionally (+) comparator inputs will access and the lamp will about-face on back the (+) ascribe goes aloft the (-) input. As the aggregate decreases, the capacitor discharges through the alongside 100K resistor and the lamps go out. You can change the acknowledgment time with a beyond or abate capacitor.
This circuit requires a able-bodied filtered ability source, it will acknowledge to actual baby changes in accumulation voltage, so you apparently will charge a ample clarify capacitor affiliated anon to the 330 ohm resistor. I managed to get it to assignment with an able bank agent ability source, but I had to use 4700uF. It formed able-bodied on a adapted accumulation with alone 1000uF.
