#include <stdlib.h>

#define MAX 29
uint8_t arr[MAX] = {1, 2, 3, ... };


/* Arrange the N elements of ARRAY in random order.
   Only effective if N is much smaller than RAND_MAX;
   if this may not be the case, use a better random
   number generator. */
void shuffle(uint8_t *array, size_t n)
{
    if (n > 1)
    {
        size_t i;
        for (i = 0; i < n - 1; i++)
        {
          size_t j = i + rand() / (RAND_MAX / (n - i) + 1);
          uint8_t t = array[j];
          array[j] = array[i];
          array[i] = t;
        }
    }
}

...

while(1) {
  srand(...);
  shuffle(&arr, sizeof(arr));
  for(uint8_t i = 0, i++, i <= MAX {
    effect(arr[i]);
  }
}

uint8_t   rnd_arr[29];

for(int i=0; i<29; i++){
   rnd_arr[i]=i;
}

for(int i=0; i<100; i++){
   uint8_t     a = rand()%29;
   uint8_t     b = rand()%29;
   swap(&rnd_arr[a], &rnd_arr[b]);
}