Comparing two arrays, sending the result to Robertsonics MP3 Trigger

Projects Programming
1

Hello All,

I'm running into a wall on what I thought would be a pretty simple program.
I'll try to briefly describe what I'd like the sketch to do, then post the code with comments.

I'd like to continuously take readings from a force-sensing resistor.
If the reading is above a threshold, I'd like to tell the MP3 trigger to start playing.
As long as the sensor keeps getting relatively frequent readings above 0 (or some other arbitrary threshold),
I'd like it to keep playing. If the sensor gets no readings for a set period of time (3 seconds or so?) I'd like the trigger to stop playing.

Simple, right? Well, not for me, it turns out.

To determine if the sensor had received a number of consecutive zeros, I put in two arrays. One to store the sensor values and one of nothing but zeros.
I then wrote a simple boolean function to continuously compare the two arrays. If the arrays are equal (meaning, both are all zero), that should mean that
the sensor received no readings for a while.

As far as I can tell, the code below should do what I described, but it does not. When the trigger starts playing a track it just keeps on playing, no matter how many zeros.

I have two questions for the forum:

  1. Is there anything in my code that would cause this unexpected result ( I admit I'm not great with programming)??
  2. Is creating two arrays to determine if and when the sensor gets no reading a good way to do it? I would imagine there is a simpler or more elegant way of achieving this, but two arrays is my best guess so far.

I'd really appreciate any help on this. Many Thanks!

Here's the code:

/*Continuously read analog sensor values and compare them to an equal-sized
array of zeros.  Serially communicate with Robertsonics MP3Trigger*/

#define SENSOR 0      //In this case, a force-sensing resistor

int num = 30;
int val[30];          //array of sensor values
int zero[30];         //array of zeros
boolean isPlaying;

void setup() {
  Serial.begin(38400);
}

void loop() {
  
  int threshold = 20; 
  int i;
 
  for (i = 0; i < num; i = i + 1) {
    val[i]=analogRead(SENSOR);             //store sensor values
    zero[i] = 0;                           //store zeros
      delay(200);
      Serial.println(val[i]);
  
      if((val[i] >= threshold) && (isPlaying == false)) {
        Serial.write('p');                //Serial command for playing a track
        Serial.write(1);                  //track number
        isPlaying == true;
        delay(3000);
      }
  }
  
  if ((arrayCompare(val, zero, num, num)==true) && (isPlaying==true)) {  /* if 30 consecutive
                                                                         sensor values = 0*/
      
    
    Serial.write('O');                //Serial command for stop/start
    isPlaying == false;
  }
}


boolean arrayCompare(int x[], int y[], int len_x, int len_y) {    /*compare sensor values to 
                                                                  array of zeros.  Return true
                                                                  if all sensor values = 0 */
  
  int i;              
  for(i = 0; i < len_x; i++) {
    if (x[i] == y[i]) {
      return true;
    } 
      return false
  }
}
2

Your array compare function returns true as soon as one pair of elements matches. That does not agree with your post or the comments.

There is no reason to store an array of 0s to compare to.

You'd be better off recording when (using millis()) a non-zero reading occured, and periodically (every pass through loop(), probably) comparing now (also using millis()) to when the last non- zero reading occured. If the difference is greater than some value, send the data to turn the device off.

3

Thanks, Paul.
I'll try this as soon as I get a chance.
I was hoping for just this kind of function!

4

Well, after taking Paul's advice and wrestling with the code for way too long, I think I've got it working.
Millis() was definitely the way to go, and tweaking the code seems to allow the sketch to do what I need it to on a basic level.

Still, I realize there may be something else that I'm missing, or some other dumb syntax error in the code.

Here is the modified code, allowing Arduino to send serial messages to a Robertsonics .mp3 trigger depending on how much time has passed since the initial desired value is received from a sensor.

Good lord, this should not have taken so long, but it's good progress!

#define SENSOR 0 

int val = 0;           //Stores sensor value
int isPlaying = 0;  //toggle for whether sound is playing

unsigned long time_start = 0;   //stores sensor values if they are above threshold
unsigned long time_stop = 0;    //stores all later sensor values for comparison
unsigned long difference = 10000;  

void setup() {
  Serial.begin(38400);
}

void loop() {
  
  int threshold = 20; 
  val = analogRead(SENSOR);  //take a sensor reading
  
  delay(300);
  Serial.println(val);
  
  if((val >= threshold) && (isPlaying == 0)) {
        Serial.write('p');    //Serial message for "play"
        Serial.write(1);      //Serial message for "track 1"
        time_start = millis();  //store time of value above threshold
        isPlaying = 1;        //playing is "on"
        Serial.println(time_start);
        delay(3000);
  }
  
  val = analogRead(SENSOR);  //take another reading
  time_stop = millis();      //store the time of that reading
  
  if((val >= threshold) && (isPlaying == 1)) {    
    time_start = millis();    //if any value is above threshold, make it the new time_start
  }

 if(((time_stop - time_start) > difference) && (isPlaying ==1) && (val < 5)){  //if a low value happens long enough after a time_start
      Serial.write('O');    //Serial message for "stop"
      isPlaying = 0;        //playing is "off
      delay(3000);
  }
}

Cheers!