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Phototransistor

Phototransistor

This example shows how to use a phototransistor to determine the relative ambient light.

Hardware Required

  • Arduino Board
  • Phototransistor supplied in the oddWires kit
  • 220 ohm resistor (one of the 10 supplied in the oddWires kit)

Circuit

To build the circuit, attach one end of a 220 ohm resistor to GND and connect the other to phototransistor emitter (shorter wire). Then attach the other end of the phototransistor (longer wire) to Arduino analog pin A0. The ambient light is proprtional to the analog voltage measured.

 

arduino-thermistor-voltage-divider-bb.png

Code

/*

Analog Input
Demonstrates analog input by reading an analog sensor on analog pin 0 and
turning on and off a light emitting diode(LED) connected to digital pin 13.
The amount of time the LED will be on and off depends on
the value obtained by analogRead().

The circuit:
* Potentiometer attached to analog input 0
* center pin of the potentiometer to the analog pin
* one side pin (either one) to ground
* the other side pin to +5V
* LED anode (long leg) attached to digital output 13
* LED cathode (short leg) attached to ground

* Note: because most Arduinos have a built-in LED attached
to pin 13 on the board, the LED is optional.


Created by David Cuartielles
modified 30 Aug 2011
By Tom Igoe

This example code is in the public domain.

http://www.arduino.cc/en/Tutorial/AnalogInput

*/

int sensorPin = A0; // select the input pin for the potentiometer
int ledPin = 13; // select the pin for the LED
int sensorValue = 0; // variable to store the value coming from the sensor

void setup() {
  // declare the ledPin as an OUTPUT:
  pinMode(ledPin, OUTPUT);
  Serial.begin(9600);
}

void loop() {
  // read the value from the sensor:
  sensorValue = analogRead(sensorPin);
  Serial.println(sensorValue);
  // turn the ledPin on
  digitalWrite(ledPin, HIGH);
  // stop the program for <sensorValue> milliseconds:
  delay(sensorValue);
  // turn the ledPin off:
  digitalWrite(ledPin, LOW);
  // stop the program for for <sensorValue> milliseconds:
  delay(sensorValue);
}

 

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