Arduino Firmware Breakdown

Embedded System Responsibilities

Imported Libraries & Hardware Drivers

The firmware begins by importing multiple communication and graphics libraries. These libraries provide hardware abstraction layers between the RP2040 and its peripherals.

#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>

Wire.h — I2C Communication Bus

The Wire library initializes and manages the synchronous I2C protocol. This protocol uses:

• SDA → Serial Data Line
• SCL → Serial Clock Line

The OLED exists as a separate hardware node connected through this shared communication bus.

Adafruit_GFX.h — Graphics Engine

The graphics library provides primitive rendering instructions such as:

• Lines
• Circles
• Pixels
• Text
• Rectangles

Adafruit_SSD1306.h — OLED Driver

This driver translates graphics instructions into SSD1306-compatible display commands. Without this driver the RP2040 cannot understand the OLED memory architecture.

OLED Display Configuration

The firmware next defines the physical geometry of the display.

#define SCREEN_WIDTH 128
#define SCREEN_HEIGHT 64
#define VIS_ZONE 44

Adafruit_SSD1306 display(
    SCREEN_WIDTH,
    SCREEN_HEIGHT,
    &Wire,
    -1
);

This line constructs the OLED display object. All future graphics commands are routed through this object.

Global Memory Architecture

const int btnPin = 26;

struct Scan {
  int y1;
  int y2;
};

Scan library[5];

int savedTotal = 0;
int currentIdx = 0;

Push Button Pin

The push button is connected to GPIO pin 26. The firmware later configures this pin as an INPUT_PULLUP configuration.

Struct-Based Scan Storage

The firmware introduces a custom structure called Scan. This behaves as a lightweight embedded database record.

Each stored scan contains:

• First contour coordinate
• Second contour coordinate

The array:

Scan library[5];

allocates memory for five contour profiles directly inside SRAM.

Finite State Machine Architecture

int currentState = 0;
int menuOption = 0;

This design prevents conflicting interface behaviors. Only the logic relevant to the active state becomes executable.

Hardware Initialization — setup()

The setup function executes once during system startup. Its responsibility is to initialize every hardware subsystem.

void setup() {

  Serial.begin(115200);

  Wire.setSDA(6);
  Wire.setSCL(7);
  Wire.begin();

  display.begin(SSD1306_SWITCHCAPVCC, 0x3C);

  pinMode(btnPin, INPUT_PULLUP);

  display.setTextColor(WHITE);
}

Serial.begin(115200)

Initializes UART communication between the RP2040 and the laptop. The baud rate must exactly match the Python listener configuration.

Wire.begin()

Activates the RP2040 internal I2C controller hardware. Without this call the OLED receives no communication frames.

display.begin(..., 0x3C)

Initializes the OLED using I2C address 0x3C. This behaves like the display's network address on the local bus.

Main Runtime Loop

The loop function behaves as the embedded runtime engine. It continuously:

• Samples analog inputs
• Processes button events
• Updates the display
• Handles menu states

int v1 = map(analogRead(A2), 0, 1023, VIS_ZONE, 8);
int v2 = map(analogRead(A1), 0, 1023, VIS_ZONE, 8);

The potentiometers generate raw ADC values from 0–1023. The map function rescales those values into OLED pixel coordinates.

Multi-Function Button System

A single push button controls:

• Saving scans
• Opening the library
• Entering menus
• Scrolling menu options
• Confirming actions

if (digitalRead(btnPin) == LOW)

The firmware constantly checks whether the button transitions LOW. If pressed, the system begins timing the interaction duration.

if (duration > 800)

Any press longer than 800 milliseconds becomes a long press event.

if (millis() - lastClick < 300)

The firmware compares timestamps to determine whether the interaction was:

• Single click
• Double click

UART Communication & Coordinate Streaming

This section performs the primary networking operation of the firmware. The RP2040 converts graphical contour data into structured coordinate packets.

Serial.println("START_DATA");

This line acts as a transmission handshake key. The Python application listens for this exact phrase before beginning extraction.

float mmY1 = map(library[i].y1, VIS_ZONE, 8, 0, MAX_TRAVEL);
float mmY2 = map(library[i].y2, VIS_ZONE, 8, 0, MAX_TRAVEL);

The firmware converts OLED pixel coordinates back into real mechanical distances measured in millimeters.

Serial.print("SCAN:");
Serial.print(i);
Serial.print(",");
Serial.print(x1);
Serial.print(",");
Serial.print(mmY1);
Serial.print(",");
Serial.print(x2);
Serial.print(",");
Serial.println(mmY2);

Each scan becomes a structured UART packet formatted as:

SCAN:0,0.0,12.5,3.0,15.2

Embedded Graphics Rendering

display.drawLine(15, y1, 113, y2, WHITE);
display.fillCircle(15, y1, 2, WHITE);
display.fillCircle(113, y2, 2, WHITE);

The OLED therefore behaves as a live vector visualization interface.

Complete Firmware Architecture Summary