This analyst is, a sensitive instrument, in the frequency changes and width of a acoustic signal. Thus the brightness of LED that turns on each moment of is proportional signal width, while the colour of proportionally frequency. The circuit input sensitivity is regulated with R2, in order that in powerful signals they turn on the red LED, in the middle the yellow LED and in the low green LED. The display unit, is constituted by 3 lines of 10 LED the every, what is checked by a counter decoder (IC2). Two gates IC?-b, function as the IC2, with the R6 regulate the frequency. When does not exist signal in the input, then no one LED does not turn on. As soon as it will be applied signal, then the LED will begin to blink depending on the rythm and the intensity of signal.
Can experiment with the prices of resistances R4, R5, so that you find the value that suits in like your. Initially it can they are placed trimmer 1K?, in the place of R4, R5 and after is found the suitable value, they are replaced with permanent resistances. What it wants it can it adds also other LED, adding other a completed same press with the IC2. The particular circuit does not have the claim, the precision of measurement input signal.
R1= 1K8Kohm R6= 100Kohm trimmer IC1= LM3915
R2= 100Kohm trimmer C1= 100nF 100V IC2= 4017
R3= 1Kohm D1....10= RED LED IC3= 4011
R4= 100 ohm.....1Kohm D11....20= YELLOW LED
R5= 100 ohm.....1Kohm D21....30= GREEN LED