A spectrum analyzer measures the magnitude of an input signal versus frequency within the full frequency range of the instrument.

In this project is presented a very simple way in which such a device can be made with the help of only a few components:
     - Arduino Nano microcontroller
     - 16X2 LCD display   
     - capacitor 47 nF   and
     - trimer potentiometer 10 kOhm
   The "FHTSpectrumAnalyzer" project was chosen as the source for creating the spectrum analyzer and minor changes were made to the code.  The display connection via I2C was changed to 4-bit mode, the ADC reference voltage was switched to internal 1.1 V.  You will also need the FHT.h library. 
    An audio signal directly through a 47 nF capacitor is fed to analog input A1, the spectrum analyzer has an automatic gain of the input signal, which improves the visual image of the spectrum analyzer.
     You can also use the button to select one of the six visual modes.

Finally, the device is housed in a convenient box that I also use for multiple devices. Otherwise, the device can be used as an effective visual detail within a DIY amplifier or preamlifier.