Let's measure the brightness of the light.

1. 1
Arduino Tutorial #3
- Measuring the light -
Dong Ho Son
POSTECH
Pohang, Korea
donghoson@postech.ac.kr

2. 2
Measuring the light - Overview
 Sensor: Analog  Digital
• Analog : continuous
• Digital : discrete
 Photoresistor (or Light-Dependent Resistor, LDR)
• A light-controlled variable resistor
• The resistance increases/decreases according to the brightness
 Let’s configure the circuit
• The brightness of the LED is changed according to the brightness of the
environment
• If dark, the LED also would be dark
• If bright, the LED also would be bright
source: wikimedia.org

3. 3
Measure the light - Circuit
 Configure the circuit
+-
2kΩ
220Ω
Source: pixabay.com/photo-2168193

4. 4
Measuring the light - Sketch (1/3)
 setup() { }
• pinMode(10, OUTPUT);
− Prepare the mode of pin
− We will use pin #10
− We will order to LED  OUTPUT
• Serial.begin(9600);
− Prepare the serial communication to get
the value of light from the sensor
− 9600: serial communication speed
– 9600 bits per second is the default for the Arduino

5. 5
Measuring the light - Sketch (2/3)
 loop() { }
• int val = analogRead(A4);
− Read the analog value of light
• analogWrite(10, val/4);
− Turn on the LED
− Different from digitalWrite();
– digitalWrite(); just has HIGH or LOW
− Brightness of LED is controlled by ‘val/4’
− val  10 bit , val/4  8 bit
− analogWrite() uses 8 bit of digital pin

6. 6
Measuring the light - Sketch (3/3)
 loop() { }
• Serial.print(“ Brightness = ”);
− It prints the text “ Bightness = ”
to the serial console
• Serial.println(val/4);
− It prints the value of ‘val/4’ to the serial console
− Also changes the line (newline)
• Delay(10);
− Need 10ms to check step-by-step

7. 7
Measuring the light - Result
 The brightness of the LED is being changed!
+-
Brightness = 127
Brightness = 153
Brightness = 128
Brightness = 156
Brightness = 127
Brightness = 156
Brightness = 127
Brightness = 156
Brightness = 125
Brightness = 155
Brightness = 124
Brightness = 158
Brightness = 129
Brightness = 156
Brightness = 127
Brightness = 153
Brightness = 125
Source: pixabay
2kΩ
220Ω
Source: pixabay.com/photo-2168193