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Arduino tutorial #3
This document describes how to measure light levels using an Arduino. It explains that a photoresistor (LDR) is used as a light sensor, whose resistance changes with brightness. The circuit connects the LDR to an LED and Arduino analog pin. Code samples show configuring the Arduino pin modes, reading the LDR value, and using it to set the LED brightness level. The result is the LED brightness changing in response to environmental light levels measured by the LDR.
Arduino tutorial #3
- 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