Error increases as frequency increases using FreqCount Library in Arduino Uno Board

[SumanTheBob]

include

include

LiquidCrystal lcd(5, 4, 3, 2, 1, 0);

void setup() { Serial.begin(9600); lcd.begin(8, 2); lcd.print("Freq:"); FreqCount.begin(1000); }

void loop() { if (FreqCount.available()) { unsigned long count = FreqCount.read(); lcd.setCursor(0, 1); lcd.print(count); lcd.print(" "); } } I am using this program for measuring the signal frequency of a square wave (8 v p-p) from a very good function generator with frequency varying from 2 kHz to 10 kHz. But the error increases as the frequency increases. (For 2 kHz the LCD output is 2003 Hz, for 5 kHz it is 5006 and for 10 kHz the LCD output is 10011: hence the error is always positive and it increases with frequency) Can you please guide me on why this is happening?

[colinluthier]

Are you feeding the clock of the Arduino with a calibrated source? Replacing the crystal with a TCXO will help with accuracy and stability. Alternatively you can add a bit of code for an offset for your particular crystal.

[PaulStoffregen]

You say "the error increases as the frequency increases", but to my eyes the error looks like a pretty consistent percentage of the frequency measured.