O fotorezistenta si Arduino

   Fotorezistentele sunt componente pasive, care-si modifica valoarea (rezistenta) functie de intensitatea luminoasa (au rezistent amare la intuneric si mica la lumina puternica).
   In articolul Using a Photocell este prezentat un material foarte bun, din care m-am inspirat si eu.
   Dupa ce ma incercat primele 2 exemple de acolo, am modificat sketch-ul ca la un anumit prag de intuneric sa se cupleze un releu, iar la lumina foarte slaba (intuneric), inca unul.
   Circuitul de conectare al fotorezistentei, este foarte simplu, necesitand doar o rezistenta:

iar placa cu 2 relee are comanda la pinii D7, respectiv D8.

   Logica de comanda este inversata, adica daca pe pinul de comanda este 0 logic (LOW), releul este actionat si daca este 1 logic (HIGH) este neconectat, cum am prezentat mai de mult in articolul Placa cu 4 relee pentru Arduino (.. si nu numai).

   Montajul testat arata asa (mai contine si alte parti de circuit, nefolosite):

   Pe ecran am obtinut:

 

   Sketch-ul adaptat de mine este:

/* Photocell simple testing sketch. 
 
Connect one end of the photocell to 5V, the other end to Analog 0.
Then connect one end of a 10K resistor from Analog 0 to ground
 
For more information see http://learn.adafruit.com/photocells 

niq_ro adapted software program in 20.01.2014, see http://nicuflorica.blogspot.com/
*/

 
int photocellPin = 0;     // the cell and 10K pulldown are connected to a0
int photocellReading;     // the analog reading from the analog resistor divider
 
int relayPin = 7;         // first relay control
int relayPin2 = 8;         // second relay control
 
void setup(void) {
  // We'll send debugging information via the Serial monitor
  Serial.begin(9600); 
  pinMode(relayPin, OUTPUT);  // pin "relayPin" is output pin
  pinMode(relayPin2, OUTPUT);  // pin "relayPin" is output pin
}
 
void loop(void) {
  digitalWrite(relayPin, HIGH);  // first auxiliar light is off
  digitalWrite(relayPin2, HIGH);  // second auxiliar light is off
  photocellReading = analogRead(photocellPin);  
 
  
  Serial.print(photocellReading);     // the raw analog reading
  Serial.print(" lux"); 
  // We'll have a few threshholds, qualitatively determined
  if (photocellReading < 20) {
    Serial.println(" - Dark (intuneric)"); 
    digitalWrite(relayPin, LOW);  // first auxiliar light is on
    digitalWrite(relayPin2, LOW);  // second auxiliar light is on
    Serial.println("All lights are on (Toate luminile sunt aprinse).");
    Serial.println("***********************************************");

  } else if (photocellReading < 200) {
    Serial.println(" - Dim (intunecat)");
    digitalWrite(relayPin, LOW);  // first auxiliar light is on
    digitalWrite(relayPin2, HIGH);  // second auxiliar light is off
    Serial.println("First light are on (Un circuit de lumina e aprins).");
    Serial.println("***********************************************");
  } else if (photocellReading < 500) {
    Serial.println(" - Light (lumina normala)");
    digitalWrite(relayPin, HIGH);  // first auxiliar light is off
    digitalWrite(relayPin2, HIGH);  // second auxiliar light is off
    Serial.println("All lights are off (Toate luminile sunt stinse).");
    Serial.println("***********************************************");
  } else if (photocellReading < 800) {
    Serial.println(" - Bright (lumina buna)");
    digitalWrite(relayPin, HIGH);  // first auxiliar light is off
    digitalWrite(relayPin2, HIGH);  // second auxiliar light is off
    Serial.println("All lights are off (Toate luminile sunt stinse).");
    Serial.println("***********************************************");
  } else {
    Serial.println(" - Very bright (lumina puternica)");
    digitalWrite(relayPin, HIGH);  // first auxiliar light is off
    digitalWrite(relayPin2, HIGH);  // second auxiliar light is off
    Serial.println("All lights are off (Toate luminile sunt stinse).");
    Serial.println("***********************************************");
  }
  delay(2500);
}

   Am facut si un filmulet, numit teste cu fotorezistenta, 2 relee si Arduino, in care se vede mai bine ce am explicat pana acum:

si cel in romgleza, numit photoresistor, 2 relay module and Arduino

21.01.2014

   Am desenat si schema de conexiuni, pentru a nu aparea confuzii: