Projektlabor Robotik MINTgrün

Für eine vollständige Beschreibung sowie den Originalcode besucht diese Website.

Mithilfe eines Metalldetektors ist es möglich, zu bestimmen, ob ein Objekt aus Metall besteht, bzw. um Metall zu detektieren. Der Detektor besteht hauptsächlich aus einer Spule, deren Induktivität durch das in der Nähe befindliche Metall verändert wird. Diese Änderung wird durch den Arduino gemessen und es kann festgestellt werden, ob sich Metall in der Nähe des Messaufbaus befindet.

Bauteile:
1 Arduino Nano
1 10 nF Kondensator
1 Diode
2 220 Ohm Widerstand
1 LED
etwa 5 Meter dünnes Kabel zu einer Spule gewickelt

Schaltplan des Metalldetektors als PDF

/*
 * Metal detector
 * We use the code of this project, 
 * with minor changes:
 * https://www.instructables.com/id/Simple-Arduino-Metal-Detector/
 */
 
const byte npulse = 3; // 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
 
void setup() {
  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 = 1023;
  int maxval = 0;
 
  //perform measurement
  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(20);
    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 + 10) {
      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);
    }
 
  }
 
  //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 >> 10) {   //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));
}