Input devices (Mar 27)

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Assignment
   Measure something: add a sensor to a microcontroller board that you've made and read it

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This week I decided to use a sensor of light level control. The name of this sensor is photoresistor or light dependent resistor (LDR). The LDR is a resistor whose resistance decreases with increasing incident light intensity; in other words, it exhibits photoconductivity. The Attiny can not measure changes in resistance, but it can read analog voltage values​​. I will create a voltage divider between one constant resistance and one LDR. When change the LDR resistance, I will be able to read the voltage variations, following Ohm's law V = R * I.

To do all this, I will programme an analog input of Atinny, the A0. This read value is compared with a constant value and discriminates when is dark or light to turn on or turn of the led.

Video of testing LDR sensor






This is a Arduino code example. 

/*
  Analog Input
 Analog input by reading an analog sensor on analog pin A0 and
 turning on and off a light emitting diode(LED) connected to digital pin 7.r
 
 Resistor 10k connected to VCC and A0
 LDR connected to A0 and GND
 
  
 Created by Rubén Saguar
 
 */

int sensorPin = A0;    // select the input pin for the potentiometer
int ledPin = 7;      // select the pin for the LED
int sensorValue = 0;  // variable to store the value coming from the sensor
int const sensorRef = 900;

void setup() {
  // declare the ledPin as an OUTPUT:
  pinMode(ledPin, OUTPUT);  
}

void loop() {
  // read the value from the sensor:
  sensorValue = analogRead(sensorPin);    
  if (sensorValue<=sensorRef)
  {
    // turn the ledPin on
    digitalWrite(ledPin, HIGH);  
  }
  else
  {
    // turn the ledPin off:        
    digitalWrite(ledPin, LOW);
  }   
}