Arduino Sketch (Coding)

Single-Line Comment

Anything after this on a line is ignored by the compiler; used to explain code to human readers.

/* */

Syntax used for multi-line comments in Arduino C/C++.

void setup()

A required Arduino function that runs only once when the board powers on or is reset.

void

Indicates that a function does not return any value.

void loop()

A required Arduino function that runs continuously in an infinite loop after setup() completes.

pinMode(pin, mode)

Configures a specific pin's behavior as either an INPUT, OUTPUT, or INPUT_PULLUP.

LED_BUILTIN

A constant representing the pin number of the board's onboard LED (e.g., Pin 13 on Uno, Pin 2 on many ESP32s).

OUTPUT

A pin mode setting that allows the board to send voltage out to power external components.

INPUT

A pin mode setting that configures a pin to read incoming electrical signals.

Semicolon (;)

The required character used to terminate a statement in C/C++; forgetting it is the most common beginner syntax error.

digitalWrite(pin, value)

Sets an output pin's voltage state to either HIGH or LOW.

HIGH

Represents full output voltage (5V on Uno, 3.3V on ESP32), turning connected components on.

LOW

Represents zero volts (0V or Ground), turning connected components off.

delay(ms)

Pauses program execution for a specified number of milliseconds; it is a blocking function that halts all other operations.

int

A data type used to store whole integers (both positive and negative).

Global Variable

A variable declared outside of any function, accessible by all functions and retaining its value throughout runtime.

Serial.begin(baudRate)

Initializes serial communication over USB at a specified speed (baud rate).

Baud Rate

The speed of serial communication in bits per second; must match between the board and Serial Monitor to prevent corrupted output.

Serial.print()

Sends text or values to the Serial Monitor without appending a newline at the end.

Serial.println()

Sends text or values to the Serial Monitor and appends a newline character.

counter++

Increments the value of counter by 1; shorthand for "counter = counter + 1;".

Serial Monitor

A tool in the Arduino IDE (Tools → Serial Monitor) used to view serial data sent from the board.

const

A keyword declaring that a variable's value is read-only and cannot be altered during execution.

INPUT_PULLUP

A pin mode that activates an internal resistor holding the pin HIGH when unpressed, preventing floating inputs without requiring external resistors.

Floating Pin

An unconnected input pin that randomly fluctuates between HIGH and LOW due to electrical noise.

digitalRead(pin)

Reads the digital signal of a pin and returns either HIGH or LOW.

Comparison Operator (==)

Checks if two values are equal; distinct from assignment operator (=).

Assignment Operator (=)

Assigns the value on the right to the variable on the left.

Logical NOT (!)

Flips a boolean value, changing true to false and false to true.

Logical OR (||)

Evaluates to true if at least one of the conditions listed is true.

millis()

Returns the elapsed milliseconds since the board powered on or reset; used for non-blocking timing tasks.

millis() Rollover

The resetting of the millis() timer back to 0, which occurs after approximately 49 days of continuous running.

unsigned long

A large, non-negative integer data type; required for storing values returned by millis().

bool

A data type that holds only two possible values: true or false.

Non-Blocking Code

Programming methods (like using millis()) that allow tasks to run concurrently without halting loop execution.

analogRead(pin)

Reads voltage from an analog pin and converts it into a digital integer representation via an ADC.

Analog-to-Digital Converter (ADC)

An internal hardware module that converts analog voltage levels into digital numerical values.

ESP32 ADC Resolution

12-bit resolution, yielding an analog output value ranging from 0 to 4095.

Arduino Uno ADC Resolution

10-bit resolution, yielding an analog output value ranging from 0 to 1023.

float

A data type used to store floating-point numbers containing decimal points.

Integer Division

An arithmetic operation involving only integers that drops decimal values unless explicitly converted to floating point.

ESP32 ADC1 Pins

GPIO pins 32 to 39, which remain functional for analog reading even when Wi-Fi is active (unlike ADC2 pins).

Pulse Width Modulation (PWM)

A technique that rapidly switches a digital pin on and off to simulate analog voltage variations.

Duty Cycle

The ratio of time a signal is active (HIGH) relative to its total period, controlling output intensity/brightness.

ledcAttach(pin, freq, res)

Configures a GPIO pin for PWM generation on ESP32 (Arduino core 3.x), defining its frequency and bit resolution.

ledcWrite(pin, duty)

Sets the active duty cycle value for a designated PWM pin on ESP32.

analogWrite(pin, duty)

Generates a PWM signal on designated PWM pins (marked with ~) on an Arduino Uno.

#include

A preprocessor directive that incorporates external library files into a sketch prior to compilation.

char*

A C/C++ data type representing a string (pointer to a sequence of characters).

ESP32 Wi-Fi Frequency

The wireless network band supported by ESP32 modules (2.4 GHz only; 5 GHz is unsupported).

WebServer server(port)

Instantiates an HTTP server object listening on a specified port (default HTTP port is 80).

HTTP Status Code 200

The standard HTTP response status code indicating that a request was successful (OK).

HTTP Status Code 303

An HTTP response status code indicating a redirection ("See Other") to a different URI.

Escape Character (\)

A backslash used in strings to allow special characters like quotation marks (\") to be processed as text.

WiFi.begin(ssid, password)

Initiates an asynchronous connection attempt to a Wi-Fi network using provided credentials.

WiFi.status()

Returns the current Wi-Fi connection status (e.g., WL_CONNECTED).

WiFi.localIP()

Retrieves the IP address assigned to the board by the network router.

server.on(path, handler)

Binds an incoming HTTP request route/path to a specific function handler.

server.handleClient()

Checks for incoming web client requests and triggers their corresponding handler functions; must be called continuously in loop().