It can measure the frequency of signals with rectangular, sinusoidal and triangular shapes. Its measurement range is from a few hertz to 6.5 Megahertz.

The code is simple thanks to "FreqCount" and "LedControl" libraries. The device consists of several components:
     - Arduinio Nano microcontroller
     - Shaping amplifier board
     - 8 Digit 7 Seg Display 
     - and input jack

If we measure the frequency only on rectangular signals, then the input circuit (shaping amplifier) can be omitted, in which case we carry the signal directly to the D5 pin of the Arduino.  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.