Metal detector using Arduino

[velvetvodka]

I made a metal detector using Arduino for my college project. Our metal detector is detecting the metal. Our professor told us to implement a counter to count every time the metal is detected.We implemented the count. But the problem is every time our led flickers the count goes up.
I do not know how to rectify it.
Here's the code:

const byte npulse = 12; // number of pulses to charge the capacitor before each measurement
 
const byte pin_pulse = A0; // sends pulses to charge the capacitor (can be a digital pin)
const byte pin_cap  = A1; // measures the capacitor charge
const byte pin_LED = 12; // LED that turns on when metal is detected
#define Interval  5000
int numberOfTurnOn = 0;

unsigned long msecLst = 0;

void setup() {
  Serial.begin(9600);
  pinMode(pin_pulse, OUTPUT);
  digitalWrite(pin_pulse, LOW);
  pinMode(pin_cap, INPUT);
  pinMode(pin_LED, OUTPUT);
  digitalWrite(pin_LED, LOW);
}
 
const int nmeas = 256; //measurements to take
long int sumsum = 0; //running sum of 64 sums
long int skip = 0; //number of skipped sums
long int diff = 0;      //difference between sum and avgsum
long int flash_period = 0; //period (in ms)
long unsigned int prev_flash = 0; //time stamp of previous flash
 
void loop() {
 
  int minval = 2000;
  int maxval = 0;
 
  //perform measurement
  unsigned long msec = millis ();

  long unsigned int sum = 0;
  for (int imeas = 0; imeas < nmeas + 2; imeas++) {
    //reset the capacitor
    pinMode(pin_cap, OUTPUT);
    digitalWrite(pin_cap, LOW);
    delayMicroseconds(40);
    pinMode(pin_cap, INPUT);
    //apply pulses
    for (int ipulse = 0; ipulse < npulse; ipulse++) {
      digitalWrite(pin_pulse, HIGH); //takes 3.5 microseconds
      delayMicroseconds(3);
      digitalWrite(pin_pulse, LOW); //takes 3.5 microseconds
      delayMicroseconds(3);
    }
    //read the charge on the capacitor
    int val = analogRead(pin_cap); //takes 13x8=104 microseconds
    minval = min(val, minval);
    maxval = max(val, maxval);
    sum += val;
 
    //determine if LEDs should be on or off
    long unsigned int timestamp = millis();
    byte ledstat = 0;
    if (timestamp < prev_flash +12) {
      if (diff > 0)ledstat = 1;
      if (diff < 0)ledstat = 2;
    }
    if (timestamp > prev_flash + flash_period) {
      if (diff > 0)ledstat = 1;
      if (diff < 0)ledstat = 2;
      prev_flash = timestamp;
    }
    if (flash_period > 1000)ledstat = 0;
 
    //switch the LEDs to this setting
    if (ledstat == 0) {
      digitalWrite(pin_LED, LOW);
    }
    if (ledstat == 1) {
      digitalWrite(pin_LED, LOW);
    }
    if (ledstat == 2) {
      digitalWrite(pin_LED, HIGH);
    }
    if(ledstat == 2) {
            if ((msec - msecLst) > Interval)  {
                msecLst = msec;
                numberOfTurnOn++;
                Serial.println (numberOfTurnOn);
            }
        }
 
 
  }
 
  //subtract minimum and maximum value to remove spikes
  sum -= minval; sum -= maxval;
 
  //process
  if (sumsum == 0) sumsum = sum << 6; //set sumsum to expected value
  long int avgsum = (sumsum + 32) >> 6;
  diff = sum - avgsum;
  if (abs(diff)<avgsum >> 100) {   //adjust for small changes
    sumsum = sumsum + sum - avgsum;
    skip = 0;
  } else {
    skip++;
  }
  if (skip > 64) {  // break off in case of prolonged skipping
    sumsum = sum << 6;
    skip = 0;
  }
 
  // one permille change = 2 ticks/s
  if (diff == 0) flash_period = 1000000;
  else flash_period = avgsum / (2* abs(diff));
}

[Paul_KD7HB]

What is the LED telling you when it blinks?

[jremington]

@velvetvodka

every time our led flickers the count goes up

What makes the LED flicker?

[Idahowalker]

How long does the LED have to be lit for there to be metal detected? Just use the length of time the led is on to determine metal detection.

[velvetvodka]

I tried that, the metal has to be held for 5 seconds for the count to go up.

But my problem arises when the led is flickering for 5 seconds, the count goes up

[k727]

I recommend that you implement (in software) a jitter filter - see "debouncing".