Controle de Luminosidade (LDR+LEDS)

ARDUINO –  Controle de Luminosidade (LDR+LEDS)

Através deste artigo estarei disponibilizando informações sobre como funciona o LDR e algumas técnicas de programação de como efetuar o controle de luminosidade.

PARTE I – CONTROLE DE LUMINOSIDADE


Eletrônica:

Equipamento necessário:

  • 1 LDR de 10mm, 7mm ou 5mm.
  • 1 resistor de 10k de qualquer potência (1/16W,1/8W,1/4W).
  • 1 Arduino ou similar.
  • 1 cabo USB AB.

Funcionamento do LDR:

Figura 1: Foto do LDR.

O LDR é um resistor que varia sua resistência elétrica conforme a luminosidade. Ao aumentar a luminosidade incidente na superfície do LDR a resistência elétrica diminui, então quanto menor luminosidade maior a resistência. Tipicamente sem nenhuma luminosidade tem-se 4M enquanto com alta luminosidade tem-se 100.

 Figura 2: Esquema da Ligação do LDR com o Arduino. (R2 = 10k, R1 é o LDR)

Então, para o Arduino poder efetuar a leitura da luminosidade é utilizado um resistor em série para, na verdade, ler tensão pela entrada analógica.

Figura 3: Ligação do Arduino com o LDR.

Desta forma, quando houver variação de luminosidade a porta analógica irá ler a variação de tensão. Observando o desenho abaixo (com o programa Fritz) é feita a ligação como no esquema acima, o LDR se conecta ao 5V ao resistor e a porta analógica enquanto o resistor é conectado ao LDR, a porta analógica e ao terra.

Quando a luminosidade for alta, a tensão que vai para o pino analógico será muito próxima de 5V resultando em um número inteiro próximo de 1023 com a função analogRead(Pin). Quando estiver em baixa luminosidade será retornado um número próximo de 0 com a mesma função acima.

Programação:

Como iremos ler o nível de tensão com a porta analógica, iremos utilizar a função analogRead(Pin), Além disso será utilizada a comunicação com o computador para ler o inteiro que representa a luminosidade.

Utilizando o código abaixo e fazendo o Upload:

/* Inovabots – Controle de Luminosidade */

int PinoLeitura = A0; // Escolhendo o pino analógico A0

int Luminosidade;

void setup()

{

//Não há necessidade de declarar o pino analógico

Serial.begin(9600);

}

void loop()

{

//LeituraPot recebe o valor do pino A0.

Luminosidade = analogRead(PinoLeitura);

//Envia Leitura para PC.

Serial.println(“Leitura Luminosidade (0 a 1023):”);

Serial.println(Luminosidade);

Serial.println(“\n”);

delay(500);

}

Resultados:

Como no vídeo abaixo, quando incide luminosidade a leitura chega a valores altos (aprox. 970) e quando tampamos o sensor, chega-se a valores em torno de 90.

Com isso, podemos incluir condições para que de acordo com luminosidades se faça uma ação que pode ser acender LEDs.

OBS: Para observar uma passagem de valores mais rapidamente basta reduzir o delay para um número menor (lembrar que a função delay é em ms).

 

PARTE II – CONTROLE DE LUMINOSIDADE

Após a realização da leitura de nível de luminosidade, é possível acrescentar condições (na programação) e montar alguns LEDs de forma a acender conforme a luminosidade.

Eletrônica:

  • Itens da Parte I
  • 4 LEDs.
  • 4 resistores de 220R 1/8W.   (Pode-se utilizar resistência maior, a potência também pode ser maior).
Então, fazendo a ligação do Arduino aos LEDs como na figura abaixo:
Figura 4: Ligação do Arduino ao LDR  e aos LEDs.
Assim, o circuito fica parecido com o abaixo (note que o Arduino utilizado na figura abaixo é o Arduino MEGA, porém a ligação e a programação são específicos para o Arduino UNO).
Figura 5: Foto da ligação do circuito real.

Depois de conectar corretamente os componentes pode-se iniciar a programação.

Programação:

A programação da parte II é parecida com a parte I, a única diferença é que vai se existir condições para se ligar ou desligar o LED de acordo com a luminosidade.

Como a leitura da luminosidade varia entre 0 a 1023 as condições irão estar dentro desses valores possíveis, por exemplo:

  if ( Luminosidade < 840 )
  {
    digitalWrite(4,HIGH);
  }
  else 
  {
    digitalWrite(4,LOW);
  }

Quando o valor lido for menor que 840 o LED 4 irá acender e quando for maior que esse valor, irá apagar.

Abaixo temos o código completo da ligação:

/* Inovabots - Controle de Luminosidade */
int PinoLeitura = A0;    // Escolhendo o pino analógico A0
int Luminosidade;


void setup() {
  //Não há necessidade de declarar o pino analógico 
  Serial.begin(9600); 
  
  pinMode (4,OUTPUT);
  pinMode (5,OUTPUT);
  pinMode (6,OUTPUT);
}

void loop() {
  //LeituraPot recebe o valor do pino A0.
  Luminosidade = analogRead(PinoLeitura);
  
  //Envia Leitura para PC.  
  Serial.println("Leitura Luminosidade (0 a 1023):");
  Serial.println(Luminosidade);
  Serial.println("\n"); 
  
  if ( Luminosidade < 840 )
  {
    digitalWrite(4,HIGH);
  }
  else 
  {
    digitalWrite(4,LOW);
  }
  
  if ( Luminosidade < 700 )
  {
    digitalWrite(5,HIGH);
  }
  else 
  {
    digitalWrite(5,LOW);
  }
  
  if ( Luminosidade < 500 )
  {
    digitalWrite(6,HIGH);
  }
  else 
  {
    digitalWrite(6,LOW);
  }  
  
  delay(10);               
}

Ao compilar e dar upload no código, o resultado será como no vídeo abaixo:

 

 

O resultado é bem interessante, vários testes podem ser feitos com a luminosidade: com as cortinas do ambiente se fechando, apagando as luzes. Com certeza ao decorrer do dia os LEDs irão acendendo automaticamente.

*Nota, cuidado para a luz do LED não incidir no LDR, isso iria fazer o LED ficar piscando. O motivo é que quando existe diminuição de luminosidade o LED acende, e se o LED acender e incidir no LDR o Arduino vai mandar apagar o LED por conta que a luminosidade aumentou, quando o LED apagar o sistema vai detectar diminuição de luminosidade voltando ao estado inicial. Isto causa um ciclo indefinido e o LED fica oscilando.

Autor: Gabriel Liberalquino S. Lima

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Tags: Controle – Luminosidade – Monitoramento – LDR – Arduino – LED – Interação

77 responses to “Controle de Luminosidade (LDR+LEDS)

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