Arduino based Outdoor People Counter. see https://github.com/petervojtek/diy/wiki/Arduino-based-Outdoor-People-Counter

people-counter-v1.ino

#include <lowpower.h>
#include <EEPROM.h>

int currentSessionId;
int humanCount = 0;
int eepromHumanCount = 0;
long eepromLastSyncAt = 0;

const int trigPin = 9;
const int echoPin = 10;
const int humanCountedLedPin = 11;

boolean iSeeHuman = false;
boolean iTrackHuman = false;
long lastTimeISawHuman;

// once we observe a person, we count number of times the person stays in front of our device
int numberOfPingsObsevedHumanIsInRange = 0;

// minimum count of hitting a "person" by ultrasonic sensor to accept it as a person
static int minPingCountToAcceptHuman = 2;

static float maxBlackoutInMillis = 500;
static int iSeeHumanThresholdInCm = 250;

// set to true to make the LED blink everytime we count a person
const boolean DEBUG = true;

void setup() {
  LowPower.powerDown(SLEEP_8S, ADC_OFF, BOD_OFF);  
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);

  detectCurrentSessionId();

  if(DEBUG){
    pinMode(humanCountedLedPin, OUTPUT);
    blinkHumanCountedLed();


    Serial.begin(9600);
    delay(500);
    printHistory();
  }
}


void loop()
{
  iSeeHuman = pingDistanceInCm() < iSeeHumanThresholdInCm;

  if(iSeeHuman && !iTrackHuman) // we have first contact with human
  {
    numberOfPingsObsevedHumanIsInRange = 1;
    iTrackHuman = true;
    lastTimeISawHuman = millis();
  } 
  else if(iSeeHuman && iTrackHuman)  // we already recognized him and we keep tracking him
  {
    numberOfPingsObsevedHumanIsInRange++;
    lastTimeISawHuman = millis();
  } 
  else if(!iSeeHuman && iTrackHuman) 
  {
    if((millis() - lastTimeISawHuman) < maxBlackoutInMillis)
    {      
      // wo dont see him now, but we believe he may still be in sight
    }
    else 
    { // we havent seen him for too long
      iTrackHuman = false;

      if(numberOfPingsObsevedHumanIsInRange >= minPingCountToAcceptHuman){
        humanCount++;
        if(DEBUG)
          blinkHumanCountedLed();
          
        }
      }
    } 
  else  
  {
    // !iSeeHuman && !iTrackHuman - nothing to do
  }

  syncHumanCount();
  LowPower.powerDown(SLEEP_15Ms, ADC_OFF, BOD_OFF);    
}

long pingDistanceInCm(){
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);

  long durationInMicroseconds = pulseIn(echoPin, HIGH, 15 * 1000); 

  long cm  = durationInMicroseconds / 58;
  if(cm == 0){
    // when the background is too far away, the measurement may return distance = 0 cm
    // in such case we want to avoid counting this ping as a human presence
    cm = 500; 
  }

  return(cm);
}

void detectCurrentSessionId(){
  int previousSessionId = EEPROM.read(0);
  if(previousSessionId == 255) // "Locations that have never been written to have the value of 255."
    currentSessionId = 1;
  else
    currentSessionId = previousSessionId + 1;

  EEPROM.write(0, currentSessionId);
}

int majorHumanCount;
int minorHumanCount;
int majorBytePosition;
int minorBytePosition;

// we dont want to write too ofter to eeprom:
// atmel warns the eeprom may die after 100.000 r&w cycles (per single eeprom byte)
// also the 1byte write takes cca 3.3ms

void syncHumanCount()
{ 
  if((humanCount - eepromHumanCount) > 10){ 
    majorHumanCount = humanCount / 256;
    minorHumanCount = humanCount % 256;

    majorBytePosition = currentSessionId * 2 - 1;
    minorBytePosition = majorBytePosition + 1;   

    EEPROM.write(majorBytePosition, majorHumanCount);
    EEPROM.write(minorBytePosition, minorHumanCount);

    eepromLastSyncAt = millis();
    eepromHumanCount = humanCount;

  }
}

// session 1: 1,2
// session 2: 3,4
// session 3: 3*2 -1, 3*2
// session 100: [100*2 - 1, 100*2]

// majorBytePosition = sessionId*2 - 1
// minorBytePosition = sessionId*2
void printHistory()
{
  Serial.write("History\n\n");

  int sessionHumanCount;
  for(int sessionId = 1; sessionId < currentSessionId; sessionId++)
  {
    majorBytePosition = sessionId * 2 - 1;
    minorBytePosition = majorBytePosition + 1;
    sessionHumanCount = 256 * ( EEPROM.read(majorBytePosition)) + EEPROM.read(minorBytePosition);
    Serial.print("session id: ");
    Serial.println(sessionId);
    Serial.print("session count: ");
    Serial.println(sessionHumanCount);
    Serial.println();   
  }
}

void resetSessionInfoInEeprom(){
  EEPROM.write(0, 0);
}

void blinkHumanCountedLed(){
  for(int i = 0; i < 5; i++){
    digitalWrite(humanCountedLedPin, HIGH);
    delay(50);
    digitalWrite(humanCountedLedPin, LOW);
    delay(50);
  }
}