1. Frequency identification

2. three ways to deal with frequency
1.Band Pass Filter with RLC Circuit.
2.Discrete Fourier Transform(DFT) or Fast Fourier Transform(FFT).
3. Digital Frequency Meter

3. 1.Band Pass Filter with RLC Circuit.
1.Capacitor passes high frequency signal and blocks low frequency signal
2.Inductor passes low frequency signal and blocks high frequency signal

4. 2.Discrete Fourier Transform(DFT) or Fast Fourier Transform(FFT)
1. Convert the sampled function from time
domain to thefrequency domain.
2. Separate merged waves.

5. 3. Digital Frequency Meter (comparative method)

6. principle

7. All with Arduino Triode magnifying circuit.
Signal shaping: Arduino digital pin, adjust by adjusting magnifying circuit.
2 timers:TCCR1A and TCCR1B.
1 counter:TCNT1 (16bit, maxium:65536)
Oscillator: ATmega 2560
ATmega 2560 has two 8-bit Timer/Counters with Separate Prescaler and Compare Mode. Four 16-bit Timer/Counter with Separate Prescaler, Compare- and Capture Mode.)

8. detail
Enable overflow interrupt with TIMSK1 = 0x01, used Arduino’s interrupt pin and attachinterrupt() function.
TCCR1B as prescaler, and ATmega2560 is of 16MHz.
Board
int.0
int.1
int.2
int.3
int.4
int.5
Uno, Ethernet 2 3
Mega2560 21 20 19 18
Leonardo 1 7
𝑓= 𝑟𝑒𝑑𝑖𝑛𝑔 𝑜𝑓 𝑇𝐶𝑁𝑇1 ∗𝑝𝑟𝑒𝑠𝑐𝑎𝑙𝑒𝑟