Writing your code Your code should continuously read from the Arduino in an infinite loop. The code will stop when you press CTRL-C. Create an uint8_t array of 512 elements. For every iteration of the loop, read in 512 bytes into the array - as before, the read function may not return 512 bytes at once, so you will need to keep track of how many bytes you have received and keep calling read until you get 512 bytes. When you get to 512 bytes, call the dft function to calculate and display the DFT as histogram. I have also provided this dft function in the dftlib.c file. Note, that it is called dft not fft because it doesn't actually use the Fast Fourier Transform algorithm to calculate the DFT. This dft function expects three arguments - the array of uint8_t data items which you read from the Arduino, an array of double items into which dft puts the frequency values, and the size of the array. After calling dft, you should call dft_print, which will display the frequency spectrum. This dft_print function expects two arguments - the array of double items that was filled in by dft and the size of the array. The skeleton code can be downloaded from Compile and run your program as follows. Use the -03 option to enable maximum optimization. Otherwise, the DFT calculations may be too slow. $ gcc -03 -o dataread dataread.c dftlib.c $ ./dataread /dev/ttys2 000 --- 047 071 096 120 142 167 191 216* 240 382 407 431 456 The numbers on the left represent the frequency and the bars that go the right represent the intensity of the frequency in the received signal. When you run the code, you should be able to see what frequencies are in the signal. you press and hold down the button, you will see the frequencies change. int lookup_index = 0; #define SIN_FREQ 100 long sin_freq = SIN_FREQ; #define LOOKUP ARRAY SIZE 128UL #define PWM RESOLUTION 8 #if PWM RESOLUTION <= 8 #define PWM_t uint8_t #else #define PWM_t uint16_t #endif PWM_t *lookup_array; // lookup array for sin(2pi ft) PWM_t lookup_array1[LOOKUP_ARRAY_SIZE] { 127, 133, 139, 146, 152, 158, 164, 170, 176, 181, 187, 192, 198, 203, 208, 212, 217, 221, 225, 229, 233, 236, 239, 242, 244, 247, 249, 250, 252, 253, 253, 254, 254, 254, 253, 253, 252, 250, 249, 247, 244, 242, 239, 236, 233, 229, 225, 221, 217, 212, 208, 203, 198, 192, 187, 181, 176, 170, 164, 158, 152, 146, 139, 133, 127, 121, 115, 108, 102, 96, 90, 84, 78, 73, 67, 62, 56, 51, 46, 42, 37, 33, 29, 25, 21, 18, 15, 12, 10, 7, 5, 4, 2, 1, 1, 0, 0, 0, 1, 1, 2, 4, 5, 7, 10, 12, 15, 18, 21, 25, 29, 33, 37, 42, 46, 51, 56, 62, 67, 73, 78, 84, 90, 96, 102, 108, 115, 121 }; // lookup array for sin(2pi f t) + sin(4pi ft) PWM_t lookup_array2[LOOKUP_ARRAY_SIZE] = { }; 127, 136, 146, 155, 164, 173, 181, 189, 196, 204, 210, 216, 221, 226, 230, 233, 236, 238, 239, 239, 239, 238, 236, 234, 231, 227, 223, 219, 214, 209, 203, 197, 191, 184, 178, 172, 165, 159, 153, 147, 141, 135, 130, 125, 121, 117, 114, 111, 108, 106, 105, 104, 104, 104, 104, 105, 106, 108, 110, 112, 115, 118, 121, 124, 127, 130, 133, 136, 139, 142, 144, 146, 148, 149, 150, 150, 150, 150, 149, 148, 146, 143, 140, 137, 133, 129, 124, 119, 113, 107, 101, 95, 89, 82, 76, 70, 63, 57, 51, 45, 40, 35, 31, 27, 23, 20, 18, 16, 15, 15, 15, 16, 18, 21, 24, 28, 33, 38, 44, 50, 58, 65, 73, 81, 90, 99, 108, 118 ISR(TIMER1_COMPA_vect) long temp = lookup_array[lookup_index]; OCR1B = ((temp * (OCR1A+1)) / (1<> 2); if (lookup_array != lookup_array2 && digitalRead(5)==HIGH) { digitalWrite(13,HIGH); lookup_array = lookup_array2; else if (lookup_array != lookup_array1 && digitalRead(5)==LOW) { digitalWrite(13,LOW); lookup_array = lookup_array1; } } #include #include #include #include #include #include void dft(uint8_t*, double*, int); void dft print(double, int, double); #define N 512 int main(int argc, char **argv) { char *port = argv[1]; /* Open the file */ int fd = open(port, O_RDONLY); // code to set communication rate to 9600 bits per second struct termios tio; tcgetattr(fd, &tio); cfset speed(&tio, B9600); tcsetattr(fd, 0, &tio); // reopen the serial port so that the speed change takes effect close(fd); fd = open(port, O_RDONLY); if (fd < 0) { perror("Could not open port"); exit(-1); } } uint8_t data[N]; double dftdata[N]; // TODO create a loop that continuously // // close(fd); reads N bytes from fd into the data array calls the dft function to create the frequency values calls the dft_print function to print the DFT #include #include #include #include void dft(uint8_t* x, double* X, int N) { double Xr[N]; double Xi[N]; for (int k=0; k < N; k++) { Xr[k] = 0; Xi[k] = 0; for (int n=0; n < N; n++) { double s = x[n]-128; Xr[k] += s*cos(2.0*M_PI*k*n/N); Xi[k]. -= s*sin(2.0*M_PI*k*n/N); }| } for (int k=0; k < N; k++) { X[k] = } } sqrt(Xr[k]*Xr[k] + Xi[k]*Xi[k]); #define NBUCKETS 20 void dft_print(double* X, int N, double fs) { double disp[NBUCKETS]; int bounds [NBUCKETS]; double max = 0; for (int k=0; k < NBUCKETS; k++) { int j; int lbound = (double) N/(2*NBUCKETS)*k; int ubound = (double) N/(2*NBUCKETS)* (k+1); bounds[k] = 1bound; double sum = 0; fort-hound, izuhound S for (j=lbound; j70) count = 70; printf("%031d", Irint (bounds[k]*fs/N)); for (int j=0; j < count; j++) { } } printf("*"); printf("\n"); for (int k=0; k < NBUCKETS; k++) { printf("\033[A"); } }