This sound level indicator circuit can survive used to control the intensity of a sound recording or else featuring in a disco. It has 5 measurement domains among 70 and 120 dB; performance accuracy is 0.5 dB. Microphone M1 is used to receive the acoustic indicator and is coupled to C1, C2, R1 and R2. This components, at once with the microphone’s part and with the input impedance of the amplifier form an input filter. The filtered gesture goes to operational amplifier IC1 whose sensitivity can be real switched with S2 corresponding to the five measuring domains.
D1 … D4 diodes rectifies the alternating voltage by the side of the amplifier output and feeds the indicator tool through R9. D5 is used now order to keep the sound level gauge indicator touching far above the ground voltages; it limits the rectifier’s output voltage whilst the sound level is too high.
On standard conditions the input current is with reference to 2 mA with the purpose of is why the circuit can live powered with 2 x 9V batteries. S1 switch is used to disconnect the sound level measuring device device following measurement. The indicator tool must experience a graded size appearing in dB with the utmost set great store by of +10.