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Pin Multiplexing on Seeed Studio XIAO nRF52840 (Sense)

Seeed Studio XIAO nRF52840 (Sense) has rich interfaces. There are 11 digital I/O that can be used as PWM pins and 6 analog inputs that can be used as ADC pins. It supports all three common serial communication interfaces such as UART, I2C, and SPI. This wiki will be helpful to learn about these interfaces and implement them in your next projects!

The basic functions here perform both well for both Seeed Studio XIAO nRF52840 Arduino libraries.

Digital​

Connect a pushbutton to Pin D6 and an LED to Pin D10. Then upload the following code to control the ON/OFF of LED using the pushbutton.

const int buttonPin = 6;     // pushbutton connected to digital pin 6
const int ledPin =  10;      // LED connected to digital pin 10
 
int buttonState = 0;         // variable for reading the pushbutton status
 
void setup() {
  // initialize the LED pin as an output:
  pinMode(ledPin, OUTPUT);
  // initialize the pushbutton pin as an input:
  pinMode(buttonPin, INPUT);
}
 
void loop() {
  // read the state of the pushbutton value:
  buttonState = digitalRead(buttonPin);
 
  // check if the pushbutton is pressed. If it is, the buttonState is HIGH:
  if (buttonState == HIGH) {
    // turn LED off:
    digitalWrite(ledPin, HIGH);
  } else {
    // turn LED on:
    digitalWrite(ledPin, LOW);
  }
}

Digital as PWM​

Connect an LED to Pin D10. Then upload the following code to see the LED gradually fading.

int ledPin = 10;    // LED connected to digital pin 10

void setup() {

}

void loop() {
  // fade in from min to max in increments of 5 points:
  for (int fadeValue = 0 ; fadeValue <= 255; fadeValue += 5) {
    // sets the value (range from 0 to 255):
    analogWrite(ledPin, fadeValue);
    // wait for 30 milliseconds to see the dimming effect
    delay(30);
  }

  // fade out from max to min in increments of 5 points:
  for (int fadeValue = 255 ; fadeValue >= 0; fadeValue -= 5) {
    // sets the value (range from 0 to 255):
    analogWrite(ledPin, fadeValue);
    // wait for 30 milliseconds to see the dimming effect
    delay(30);
  }
}

Analog​

Connect a potentiometer to Pin A5 and an LED to Pin D10. Then upload the following code to control the blinking interval of the LED by rotating the potentiometer knob.

const int sensorPin = 5;
const int ledPin =  10; 
void setup() {
  // declare the ledPin as an OUTPUT:
  pinMode(sensorPin, INPUT);
  pinMode(ledPin, OUTPUT);
}
 
void loop() {
  // read the value from the sensor:
  int sensorValue = analogRead(sensorPin);
  // 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);
}

Serial​

Use Serial1 to use the UART via GPIO instead of USB. You can use both concurrently as well. Use pin D6 as the TX pin of UART and pin D7 as RX pin of UART to send the "Hello World!" message. 

void setup() {
    Serial1.begin(115200);
    while (!Serial1);
}
 
void loop() {
    Serial1.println("Hello World!");
    delay(1000);
}

I2C​

Grove - OLED Display 1.12 (SH1107)Seeed Studio XIAO nRF52840 (Sense)
GNDGND
VCC5V
SDASDA
SCLSCL

pir

  • Step 2. Open Arduino IDE, navigate to Sketch > Include Library > Manage Libraries...

  • Step 3. Search for u8g2 and install it

pir

  • Step 4. Upload the following code to display text strings on the OLED Display
#include <Arduino.h>
#include <U8g2lib.h>
#include <SPI.h>
#include <Wire.h>
 
U8G2_SH1107_SEEED_128X128_1_SW_I2C u8g2(U8G2_R0, /* clock=*/ 5, /* data=*/ 4, /* reset=*/ U8X8_PIN_NONE);
 
void setup(void) {
  u8g2.begin();
}
 
void loop(void) {
  u8g2.firstPage();
 
  do {
    u8g2.setFont(u8g2_font_luBIS08_tf);
    u8g2.drawStr(0,24,"Hello Seeed!");
  } while ( u8g2.nextPage() );
}

SPI​

Grove - OLED Display 1.12 (SH1107)Seeed Studio XIAO nRF52840 (Sense)
GNDGND
5V5V
SCLSCK
SIMOSI
RESD3
D/CD4
CSD5

pir

  • Step 2. This OLED display supports both I2C and SPI communication, and the default model is I2C. To use SPI mode, you need to refer Grove - OLED Display 1.12 (SH1107) V3.0 wiki to change the OLED display communication to SPI before proceeding further

Note: Make sure U8g2 library is installed from the previous steps.

  • Step 3. Upload the following code to display text strings on the OLED Display
#include <Arduino.h>
#include <U8g2lib.h>
#include <SPI.h>
#include <Wire.h>
 
U8G2_SH1107_128X128_1_4W_HW_SPI u8g2(U8G2_R3, /* cs=*/ 5, /* dc=*/ 4, /* reset=*/ 3);
 
void setup(void) {
  u8g2.begin();
}
 
void loop(void) {
  u8g2.firstPage();
 
  do {
    u8g2.setFont(u8g2_font_luBIS08_tf);
    u8g2.drawStr(0,24,"Hello Seeed!");
  } while ( u8g2.nextPage() );
}
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