The circuit has been designed to create a spectrum analyzer that will provide an analysis of
a sound to determine at various frequencies, the volume of sounds that make up the overall
sound spectrum.
Circuit Explanation
The device is sensitive enough to determine the sound wave components of frequency and
amplitude with the changing of frequency and the width of an acoustic signal. The
proportionality of signal width is indicated by the brightness of LED as it turns ON while the
color indicates the proportionality of frequency. In order for the red LED to turn ON in strong
signal, the sensitivity of the input circuit is adjusted by resistor R2. The middle signal is
represented by a yellow LED while the low signal is indicated the green LED.
The 10 LEDs in 3 lines comprise the display unit which is ensured the IC2 as it functions as
a counter decoder represented by the two gates ICa-b.the frequency of the counter is being
regulated by R6. No LED will turn ON in the absence of any signal in the input. The LEDs will
begin to flicker or blink depending on the intensity and tempo of the signal, once a signal
has been applied in the input. The values of the resistors R4 & R5 can be varied that will be
suitable for the desired requirements. Alternatively, this can be done by placing a 1K ohm
trimmer in place of R4 & R5 during the initial regulation and adjustment of the values. It can
be eventually removed and replaced with permanent resistors as soon as the desired
values are achieved. Additional LEDs can be added in connection to IC2 although this
circuit does not precisely measure the input signal.
Part List
R1= 1K8Kohm
R2= 100Kohm trimmer
R3= 1Kohm
R4= 100 ohm…..1Kohm
R5= 100 ohm…..1Kohm
R6= 100Kohm trimmer
C1= 100nF 100V
D1….10= RED LED
D11….20= YELLOW LED
D21….30= GREEN LED
IC1= LM3915
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