Pin Multiplexing with Seeed Studio XIAO MG24
The XIAO MG24 features up to 22 regular pins, 18 analog pins, 18 digital pins, 2 SPI, 2 UART, 2 I2C, and supports all PWM. It offers a rich variety of pins available for our use. In this wiki, I will teach you how to drive these pins, enabling us to utilize them effectively 😀!
Digital
Hardware Preparation
| Seeed Studio XIAO MG24 Sense | Seeed Studio Expansion Base for XIAO with Grove OLED | Grove - Relay |
|---|---|---|
 |  |  |
Please install XIAO MG24(Sense) onto the expansion board, and connect the relay to the A0/D0 interface of the expansion board via a Grove cable. Finally, connect XIAO to the computer via a USB-C cable.
Software Implementation
In this example, we will implement control of a relay's on/off state using a button connected to the XIAO expansion board. When the button is pressed, the relay turns on, and when the button is released, the relay turns off.
const int buttonPin = D1; // the number of the pushbutton pin
int buttonState = 0; // variable for reading the pushbutton status
const int relayPin = D0;
void setup() {
// initialize the Relay pin as an output:
pinMode(relayPin, OUTPUT);
// initialize the pushbutton pin as an input:
pinMode(buttonPin, INPUT_PULLUP);
}
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 Relay on:
digitalWrite(relayPin, HIGH);
} else {
// turn Relay off:
digitalWrite(relayPin, LOW);
}
}
Result graph
If everything goes smoothly, after uploading the program, you should see the following effect.
Digital as PWM
All GPIO pins on XIAO MG24(Sense) support PWM output. Therefore, you can use any pin to output PWM to adjust the brightness of lights, control servos, and other functions.
Hardware Preparation
| Seeed Studio XIAO MG24 Sense | Seeed Studio Expansion Base for XIAO with Grove OLED | Grove - Variable Color LED |
|---|---|---|
| |  |
Please install XIAO MG24(Sense) onto the expansion board, then connect the Variable Color LED to the A0/D0 interface of the expansion board using a Grove cable. Finally, connect XIAO to your computer via USB-C cable.
Software Implementation
In this example, we will demonstrate how to use PWM output to control the brightness of a light.
int LED_pin = D0; // LED connected to digital pin 10
void setup() {
// declaring LED pin as output
pinMode(LED_pin, OUTPUT);
}
void loop() {
// fade in from min to max in increments of 5 points:
for (int fadeValue = 0 ; fadeValue <= 255; fadeValue += 3) {
// sets the value (range from 0 to 255):
analogWrite(LED_pin, 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 -= 3) {
// sets the value (range from 0 to 255):
analogWrite(LED_pin, fadeValue);
// wait for 30 milliseconds to see the dimming effect
delay(30);
}
}
Result graph
If the program runs successfully, you will see the following running effect.
Analog
XIAO MG24(Sense) Development Board have to 12 bit ADC for high-resolution reading of analog sensor values , it can help us to read more accurate values.
Next , We will choose two sensors to reflect the characteristics of ADC .
Hadware Preparation
| Seeed Studio XIAO MG24 Sense | Grove-Variable Color LED | Grove-Rotary Angle Sensor | Seeed Studio Grove Base for XIAO |
|---|---|---|---|
| |  |  |
Software Implementation
const int analogInPin = D1; // Analog input pin that the potentiometer is attached to
const int analogOutPin = 9; // Analog output pin that the LED is attached to
int sensorValue = 0; // value read from the pot
int outputValue = 0; // value output to the PWM (analog out)
void setup() {
Serial.begin(115200);
}
void loop() {
sensorValue = analogRead(analogInPin);
outputValue = map(sensorValue, 0, 4095, 0, 255);
analogWrite(analogOutPin, outputValue);
Serial.print("sensor = ");
Serial.print(sensorValue);
Serial.print("\t output = ");
Serial.println(outputValue);
delay(100);
}
Result graph
If everything goes smoothly, after uploading the program, you should see the following effect.
UART
When working with Arduino IDE, Serial communication is an essential part of many projects. To use Serial in Arduino IDE, you need to start by opening the Serial Monitor window. This can be done by clicking on the Serial Monitor icon in the toolbar or by pressing the Ctrl+Shift+M shortcut key.
General Serial Usage
Some of the commonly used Serial functions include:
Serial.begin()-- which initializes the communication at a specified baud rate;Serial.print()-- which sends data to the Serial port in a readable format;Serial.write()-- which sends binary data to the Serial port;Serial.available()-- which checks if there is any data available to be read from the Serial port;Serial.read()-- which reads a single byte of data from the Serial port;Serial.flush()-- which waits for the transmission of outgoing serial data to complete.
By using these Serial functions, you can send and receive data between the Arduino board and your computer, which opens up many possibilities for creating interactive projects.
Here is an example program:
void setup() {
// initialize serial communication at 9600 bits per second:
Serial.begin(9600);
}
void loop() {
// send data to the serial port
Serial.println("Hello World!");
// read data from the serial port
if (Serial.available() > 0) {
// read the incoming byte:
char incomingByte = Serial.read();
// print the incoming byte to the serial monitor:
Serial.print("I received: ");
Serial.println(incomingByte);
}
// wait for a second before repeating the loop
delay(1000);
}
Usage of Serial1
According to the above XIAO MG24(Sense) Pin diagrams for specific parameters, we can observe that there are TX pin and RX pin. This is different from serial communication, but the usage is also very similar, except that a few parameters need to be added. So next, we will use the pins led out by the chip for serial communication.
#define BAUD 115200
void setup() {
Serial1.begin(BAUD);
}
void loop() {
if(Serial1.available() > 0)
{
char incominByte = Serial1.read();
Serial1.print("I received : ");
Serial1.println(incominByte);
}
delay(1000);
}
I2C
XIAO MG24(Sense) has an I2C interface that can be used for data transmission and parsing of many sensors, as well as for using some OLED screens.
Harware Preparation
| Seeed Studio XIAO MG24 Sense | Seeed Studio Expansion Base for XIAO with Grove OLED |
|---|---|
| |
The OLED display on the XIAO expansion board uses the I2C protocol and is connected to the XIAO's I2C interface through the I2C circuit on the board. Therefore, we can directly plug the XIAO into the expansion board and program it to display content on the screen.
Software Implementation
This example introduces how to use the OLED display on the Seeed Studio Expansion Base for XIAO MG24(Sense).
Step 1. Install the Seeed Studio XIAO MG24(Sense) on the Expansion board then conect the Type-C cable.
Step 2. Install the u8g2 library.
Step 3. Copy the code and stick on the Ardiono IDE then upload it.
- Download the zip file below
📄 [ZIP] smiley_face Header
- Create a header file named "smiley_face. h" and copy the contents of the downloaded zip file into the header file you created
#include <Arduino.h>
#include <U8g2lib.h>
#include <Wire.h>
#include "smiley_face.h"
U8G2_SSD1306_128X64_NONAME_F_HW_I2C u8g2(U8G2_R0, /* reset=*/ U8X8_PIN_NONE);
int xx = 20;
int yy = 10;
void setup() {
u8g2.begin();
}
void loop() {
smeil_display();
delay(500);
}
void smeil_display() {
const unsigned char* smileImages[] = {
semil1, semil2, semil3, semil4, semil5,
semil6, semil7, semil8, semil9, semil10,
semil11, semil12, semil13, semil14, semil15,
semil16, semil17, semil18, semil19, semil20,
semil21, semil22, semil23, semil24, semil25,
semil26, semil27
};
int delays[] = {
40, 50, 40, 40, 40,
40, 40, 50, 40, 40,
40, 40, 40, 50, 40,
40, 50, 40, 40, 50,
40, 50, 40, 40, 50,
50, 50, 40, 50
};
for (int i = 0; i < sizeof(smileImages) / sizeof(smileImages[0]); i++) {
u8g2.firstPage();
do {
u8g2.drawXBMP(xx, yy, 48, 48, smileImages[i]);
} while (u8g2.nextPage());
delay(delays[i]);
}
}
Result graph
SPI
The XIAO MG24(Sense) chip integrates multiple peripherals, including an SPI interface that can be used to connect external SPI devices such as flash memory, displays, sensors, and more.
Arduino Library Overview
Based on the Arduino example program provided by Waveshare, we have written an Arduino library for use with the entire XIAO series, and you can go straight to the Github for this library via the button below.
Hadware Preparation
| Seeed Studio XIAO MG24 Sense | 1.69-inch LCD SPI Display |
|---|---|
|  |
Pin Connect
After preparing the hardware as mentioned above, use jumper wires to connect the SPI interface of the XIAO and OLED. Please refer to the following diagram for the wiring method.
Installation
Since you have downloaded the zip Library, open your Arduino IDE, click on Sketch > Include Library > Add .ZIP Library. Choose the zip file you just downloaded，and if the library install correct, you will see Library added to your libraries in the notice window. Which means the library is installed successfully.
Software Implementation
After downloading and installing the library correctly, you can find two example programs named helloworld.ino and bgcolor.ino in the examples folder. The bgcolor.ino is an example to show the background color, we set the red as default. And the helloworld.ino is an to show the animation about our company logo, and this example contains the effect which the bgcolor example have.
#include <st7789v2.h>
#include "SPI.h"
#include "seeed.h"
st7789v2 Display;
void setup() {
// put your setup code here, to run once:
Display.SetRotate(270);
Display.Init();
Display.SetBacklight(100);
Display.Clear(WHITE);
}
void loop() {
// put your main code here, to run repeatedly:
// Display.SetPixel(100, 100, RED);
// Display.DrawPoint(50, 50, YELLOW, DOT_PIXEL_8X8, DOT_FILL_AROUND);
Display.DrawImage(gImage_seeed, 20, 90, 240, 47);
Display.DrawLine(15, 65, 65, 65, MAGENTA, DOT_PIXEL_2X2, LINE_STYLE_SOLID);
Display.DrawLine(15, 70, 80, 70, MAGENTA, DOT_PIXEL_2X2, LINE_STYLE_SOLID);
Display.DrawRectangle(15, 80, 265, 150, GRAY, DOT_PIXEL_2X2, DRAW_FILL_EMPTY);
Display.DrawCircle(10, 10, 25, BLUE, DOT_PIXEL_2X2, DRAW_FILL_EMPTY);
Display.DrawCircle(10, 10, 20, BLACK, DOT_PIXEL_2X2, DRAW_FILL_EMPTY);
Display.DrawCircle(10, 10, 15, RED, DOT_PIXEL_2X2, DRAW_FILL_EMPTY);
Display.DrawCircle(10, 10, 10, GREEN, DOT_PIXEL_2X2, DRAW_FILL_FULL);
Display.DrawCircle(270, 10, 25, BLUE, DOT_PIXEL_2X2, DRAW_FILL_EMPTY);
Display.DrawCircle(270, 10, 20, BLACK, DOT_PIXEL_2X2, DRAW_FILL_EMPTY);
Display.DrawCircle(270, 10, 15, RED, DOT_PIXEL_2X2, DRAW_FILL_EMPTY);
Display.DrawCircle(270, 10, 10, GREEN, DOT_PIXEL_2X2, DRAW_FILL_FULL);
Display.DrawCircle(10, 230, 25, BLUE, DOT_PIXEL_2X2, DRAW_FILL_EMPTY);
Display.DrawCircle(10, 230, 20, BLACK, DOT_PIXEL_2X2, DRAW_FILL_EMPTY);
Display.DrawCircle(10, 230, 15, RED, DOT_PIXEL_2X2, DRAW_FILL_EMPTY);
Display.DrawCircle(10, 230, 10, GREEN, DOT_PIXEL_2X2, DRAW_FILL_FULL);
Display.DrawCircle(270, 230, 25, BLUE, DOT_PIXEL_2X2, DRAW_FILL_EMPTY);
Display.DrawCircle(270, 230, 20, BLACK, DOT_PIXEL_2X2, DRAW_FILL_EMPTY);
Display.DrawCircle(270, 230, 15, RED, DOT_PIXEL_2X2, DRAW_FILL_EMPTY);
Display.DrawCircle(270, 230, 10, GREEN, DOT_PIXEL_2X2, DRAW_FILL_FULL);
Display.DrawLine(200, 160, 265, 160, GRAYBLUE, DOT_PIXEL_2X2, LINE_STYLE_SOLID);
Display.DrawLine(215, 165, 265, 165, GRAYBLUE, DOT_PIXEL_2X2, LINE_STYLE_SOLID);
Display.DrawString_EN(20, 180, "By: Jason", &Font20, WHITE, BLACK);
// Display.DrawNum(100, 220, 123456, &Font24, RED, BRED);
Display.DrawFloatNum(100, 210, 1.00, 2, &Font16, WHITE, BLACK);
}
You will find Seeed Studio logo printed on the display dynamically.
Finish up
You have learned the basic functions of the XIAO MG24 (Sense) pins. Now, let's further explore the built-in sensors.
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