How to know Arduino Sampling Rate - arduino

Question

/*
fft_adc_serial.pde
guest openmusiclabs.com 7.7.14
example sketch for testing the fft library.
it takes in data on ADC0 (Analog0) and processes them
with the fft. the data is sent out over the serial
port at 115.2kb.
*/
#define LOG_OUT 1 // use the log output function
#define FFT_N 256 // set to 256 point fft
#include <FFT.h> // include the library
unsigned long time;
void setup() {
Serial.begin(115200); // use the serial port
TIMSK0 = 0; // turn off timer0 for lower jitter
ADCSRA = 0xe5; // set the adc to free running mode
ADMUX = 0x40; // use adc0
DIDR0 = 0x01; // turn off the digital input for adc0
}
void loop() {
while(1) { // reduces jitter
cli(); // UDRE interrupt slows this way down on arduino1.0
for (int i = 0 ; i < 512 ; i += 2) { // save 256 samples
while(!(ADCSRA & 0x10)); // wait for adc to be ready
ADCSRA = 0xf5; // restart adc
byte m = ADCL; // fetch adc data
byte j = ADCH;
int k = (j << 8) | m; // form into an int
k -= 0x0200; // form into a signed int
k <<= 6; // form into a 16b signed int
fft_input[i] = k; // put real data into even bins
Serial.print("input ");
Serial.print(i);
Seirla.print(" = ");
Serial.println(k);
fft_input[i+1] = 0; // set odd bins to 0
}
fft_window(); // window the data for better frequency response
fft_reorder(); // reorder the data before doing the fft
fft_run(); // process the data in the fft
fft_mag_log(); // take the output of the fft
sei();
Serial.println("start");
for (byte i = 0 ; i < FFT_N/2 ; i++) {
Serial.print("\t output");
Serial.print(i);
Serial.println(fft_log_out[i]); // send out the data
}
}
}
Im using this FFT example code for FFT
cli(); // UDRE interrupt slows this way down on arduino1.0
for (int i = 0 ; i < 512 ; i += 2) { // save 256 samples
while(!(ADCSRA & 0x10)); // wait for adc to be ready
ADCSRA = 0xf5; // restart adc
byte m = ADCL; // fetch adc data
byte j = ADCH;
int k = (j << 8) | m; // form into an int
k -= 0x0200; // form into a signed int
k <<= 6; // form into a 16b signed int
fft_input[i] = k; // put real data into even bins
Serial.print("input ");
Serial.print(i);
Seirla.print(" = ");
Serial.println(k);
fft_input[i+1] = 0; // set odd bins to 0
}
in this input part How much input time period?
Theres no delay(); function in this example
while(!(ADCSRA & 0x10)); // wait for adc to be ready
this line work like delay() function? and this function how long wait for Analog0?

Answer 1

The sample rate is set in wiring.c:
https://code.google.com/p/arduino/source/browse/trunk/hardware/cores/arduino/wiring.c?r=565#210
So on an 16mHz arduino has a maximum sample rate of at 9600hz, but the real sample rate highly depends on on the delay you have between conversions.
As your baud rate is pretty high and you don't do a lot of calculation it should somehow be next to 9600hz.
update:
there's a more accurate answer here: https://arduino.stackexchange.com/a/701