3. Digital Read

Sensors capture real-world information, which is then communicated to the main board via pins (some digital, some analog) so that the computer can know the reality of the situation.

Therefore, the Arduino board can know the working status of digital sensors by reading the value of digital pins like buttons, IR obstacle avoidance module.

Here are the required functions.

  • pinMode(pin, mode): Configure the specific pin as INPUT or OUTPUT, here it needs to be set as INPUT.

    Syntax

    pinMode(pin, mode)

    Parameters

    • pin: the Arduino pin number to set the mode of.

    • mode: INPUT, OUTPUT, or INPUT_PULLUP.

  • digitalRead(pin): Read the value (level state) from the specified digital pin.

    Syntax

    digitalRead(pin)

    Parameters

    • pin: the Arduino pin number you want to read

    Returns

    HIGH or LOW

Example of Digital Read

int ledPin = 13;  // LED connected to digital pin 13
int inPin = 7;    // pushbutton connected to digital pin 7
int val = 0;      // variable to store the read value

void setup() {
   pinMode(ledPin, OUTPUT);  // sets the digital pin 13 as output
   pinMode(inPin, INPUT);    // sets the digital pin 7 as input
}

void loop() {
   val = digitalRead(inPin);   // read the input pin
   digitalWrite(ledPin, val);  // sets the LED to the button's value
}

Notes and Warnings

  1. Pull Up & Pull Down.

    digitalRead() may produce random, indeterminate values if the pin is not getting a level signal. So directing the input pins to a known state can make the project more reliable. When using an input component such as a button, it is usually necessary to connect a pull-up or pull-down resistor in parallel to the digital input pin.

    Apart from connecting a pull-up resistor, you can also set the pin mode to INPUT_PULLUP in the code, for example pinMode(pin,INPUT_PULLUP). In this case, the pin will access the Atmega’s built-in pull-up resistor via software, and it will have the same effect as connecting a pull-up resistor.

  2. About Pin13.

    All digital pins (1-13) on the R3 board can be used as digitalRead(). But digital pin 13 is more difficult to use as a digital input than other digital pins. Because it connects an LED and resistor, it is soldered on most boards. If you enable its internal 20k pull-up resistor, it will hang around 1.7V instead of the expected 5V because the onboard LED and series resistor pull the voltage level low, which means it always returns LOW. If you must use pin 13 as a digital input, set its pinMode() to INPUT and use an external pull-down resistor.

  3. Analog pins.

    If the digital pins are not enough, the analog pins (A0-A5) can also be used as digital pins. It needs to be set to INPUT with pinMode(pin,mode).

Related Components

Below are the related components, you can click in to learn how to use them.