Its measurement range is from a few hertz to 6.5 Megahertz. Three measurement time intervals are also available - 0.1, 1 and 10 seconds. If we measure only rectangular signals, then there is no need for a shaping amplifier and the signal is fed directly to the digital pin 5 from Arduino.
   The code is very simple thanks to the "FreqCount" library which you can also download below.

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The device is very simple and consists of several components:

      - Arduino Nano microcontroller
      - Shaping amplifier board
      - LCD display
      - Input signal shape selector
      - Input JACK
      - and Time interval switch : we can choose three intervals 0.1 -1 -and 10 seconds . 

As you can see in the video, the instrument is very precise in the whole range, and we can also calibrate the frequency meter with the simple procedure described below: 

   In the Arduino libraries folder find the FreqCount library, 
in the FreqCount.cpp file find the lines: 
    #if defined (TIMER_USE_TIMER2) && F_CPU == 12000000L 
    float correct = count_output * 0.996155; 
and replace them with:
    #if defined (TIMER_USE_TIMER2) && F_CPU == 16000000L 
    float correct = count_output * 1.000000;  
where 1.000000 is your correction factor, the
correction must be carried out by applying 1 MHz to the input of the frequency meter.
After changing the file, upload a new sketch to the Arduino board.

   Finally, the frequency meter is built into a suitable plastic box and is another useful instrument in the electronic laboratory.