Embedded Programming #

Intro #

In this page, I will introduce how I made and tested the Xiao board. This will be divided into three stages.

• Preparation (hardware and software)
• Testing (NeoPixel LED)
• Final (Adding serial connectivity)

Preparation #

Hardware: Soldering #

Soldering this board is harder than I thought. Struggled to manage to keep it nice and clean while making all the solder joints in same size.

Fortunately, the final outcome seems nice and clean. Satisfied.

Software: Arduino IDE #

First thing to do this to install the board by add the configuration file url.

Then install the board in the IDE. Search for “rp2040”.

Select the right board and port.

Install Neo-pixel library.

Testing: Neo-pixel #

I made minor changes to the example program for the Neo-pixel library, making the color change gradually rather than directly. The color still have big shift when the value hit 255, but that would be easily fixed.

Final: Adding serial connectivity #

With the final program, I decided to add serial button detection and led all in one program.

The program imitates the basic operation of a web server. The led serve as a identification, button as the power button to switch it on/off, and use serial to communicate with the client which is the serial port on the computer.

State 1: Off #

When the server is off, the identification light would go off, and if you try to send something to the board via serial, the server will return a message: "Standing by, please press the button."

State 2: On #

When the server is on, the light would be turned on and change the color gradually. In this state if the board received a message, it will send the message back with a "Received:" prefix.

Press the button once would change the state of the server. When the state is changing, the board will notify the client via serial, sending "System shut down" or "System back online".

Source code #

#include <Adafruit_NeoPixel.h>
#define BUTTON D10
#define NUMPIXELS 1

int previous_state = 1; 
bool flag = true;

int Power = 11;
int PIN  = 12;

int r = 0;
int g = 127;
int b = 255;
 
Adafruit_NeoPixel pixels(NUMPIXELS, PIN, NEO_GRB + NEO_KHZ800);
 
void setup() {
  pinMode(BUTTON, INPUT_PULLUP);
  pixels.begin();
  pinMode(Power,OUTPUT);
  digitalWrite(Power, HIGH);
  Serial.begin(19200);
}
 
void loop() { 
  // Serial.print("rea: ");
  // Serial.println(digitalRead(BUTTON));
  // Serial.print("flag: ");
  // Serial.println(flag);
  // Serial.print("prevs: ");
  // Serial.println(previous_state);
  

  if(previous_state != digitalRead(BUTTON) && previous_state == 1){
    flag = !flag;
    if(flag==1){
      Serial.println("System back online.");
    }
    else{
      Serial.println("System shut down.");
    }
  }
  previous_state = digitalRead(BUTTON);

  if(flag == true){

    if(Serial.available()){
      String message = Serial.readString();  //read until timeout
      message.trim();
      Serial.print("Received: ");
      Serial.println(message);
    }

    pixels.clear();
    r = (r+3)%255;
    g = (g+2)%255;
    b = (b+1)%255;
    pixels.setPixelColor(0, pixels.Color(r, g, b));
    delay(10);
    pixels.show();

  }


  else{
    if(Serial.available()){
      Serial.readString();
      Serial.println("Standing by, please press the button.");
    }
    pixels.clear();
    //pixels.setPixelColor(0, pixels.Color(0, 0, 0));
    pixels.show();
  }
  
}