problem with hc-sr04 ultrasonic sensors

Using Arduino Project Guidance
1

Hello everyone!
I want to use 8 hc-sr04 ultrasonic sensors with arduino uno. For the first 7 sensors i want to know if there is an obstacle at 200 cm max in front of them and for the 8th sensor at 50cm. I tried the NewPing library but they are still pretty slow.
Can anyone tell me if there is something wrong with my code.This is the code that i used:

#include <NewPing.h>
 
#define SONAR_NUM     8 // Number or sensors.
#define MAX_DISTANCE 200 // Max distance in cm.
#define PING_INTERVAL 33 // Milliseconds between pings.
int k;
int k2=0;
 
unsigned long pingTimer[SONAR_NUM]; // When each pings.
unsigned int cm[SONAR_NUM]; // Store ping distances.
uint8_t currentSensor = 0; // Which sensor is active.
 
NewPing sonar[SONAR_NUM] = { // Sensor object array.
  NewPing(6, 7, MAX_DISTANCE),
  NewPing(4, A0, MAX_DISTANCE),
  NewPing(12, 13, MAX_DISTANCE),
  NewPing(8, 9, MAX_DISTANCE),
  NewPing(2, A3, MAX_DISTANCE),
  NewPing(5, A1, MAX_DISTANCE),
  NewPing(3, A2, MAX_DISTANCE),
  NewPing(10, 11, MAX_DISTANCE)
};
 
void setup() {
  Serial.begin(9600);
  pingTimer[0] = millis() + 35; // First ping start in ms.
  for (uint8_t i = 1; i < SONAR_NUM; i++)
    pingTimer[i] = pingTimer[i - 1] + PING_INTERVAL;
}
 
void loop() {
  for (uint8_t i = 0; i < SONAR_NUM; i++) {
    if (millis() >= pingTimer[i]) {
      pingTimer[i] += PING_INTERVAL * SONAR_NUM;
      if (i == 0 && currentSensor == SONAR_NUM - 1)
        oneSensorCycle(); // Do something with results.
      sonar[currentSensor].timer_stop();
      currentSensor = i;
      cm[currentSensor] = 0;
      sonar[currentSensor].ping_timer(echoCheck);
       }
  }
  //k=0;
  // The rest of your code would go here.
}
void echoCheck() { // If ping echo, set distance to array.
  if (sonar[currentSensor].check_timer())
    cm[currentSensor] = sonar[currentSensor].ping_result / US_ROUNDTRIP_CM;
}
 
void oneSensorCycle() { // Do something with the results.
k=0;
  for (uint8_t i = 0; i < SONAR_NUM; i++) {
    if(i<=6){
    if(cm[i]>0 & cm[i]<200){
       if(k==0){k=i+1;}}
       
    }
    if(i==7){
    if(cm[i]>0 & cm[i]<50){
       if(k==0){k=i+1;}}
       
    }
  }
  if (k!=k2){
  Serial.print(k);
  k2=k;}
}
2

Code compiles fine and is pretty much the NewPing15Sensor example sketch, but with 8 sensors and a different oneSensorCycle() function. I could not figure out what you are trying to achieve in your version of the oneSensorCycle() function, though. More details of what was supposed to happen and what you got will be helpful.

3

What the code does: if an obstacle is detected by any sensor, the number of the sensor is printed, but only once ( i dont want to keep sending me the same number). If no obstacle is detected by no sensor, zero is printed (only once again until something else happens). The code works. The problem is that the sensors work slowly and me (-the obstacle) i have to stand 2 or 3 seconds in front of one in order to get the number printed. I wonder if i have to change the ping interval or something else at the code or this is the best the sensors can do. Also, i have the serial begin at 9600 bps but NewPing15Sensor example sketch has 115200 bps. Is this a problem for what i want to do? (sorry if this is a stupid question)