Frequency Counter using Arduino

Ardino frequency counter. The sketch was downloaded after a search on Google. Most sketches are identical in nature and performance. There is a significant amount of variation in these oscillator/frequency counters... and the sound and frequency display show movement of nearly 100Hz. Some of this can be removed by using high more stable/high quality components. However the microcontroller does sample the length of the individual waveforms.
CIRCUIT: A CD4047 multivibrator creates a square wave who frequency is selected using a 10KΩ potentiometer and a .22uF cap. The output is transmitted to a CD40106/74HC14 Hex Schmitt trigger to stabilize the oscillation--but this part can actually be eliminated. The Arduino can tap the Q or Q-LO output of the CD4047, if desired. If an LM555 timer or a different oscillator is used, the 74HC14 is probably necessary to "square up" the wave. A speaker allows the tone to be heard and an LCD displays the audio frequency.