Arduino Pins: A Detailed Guide

Arduino boards come with various types of pins, each serving a different function. Understanding these pins is essential for working with sensors, motors, displays, and communication modules.

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🔹 1. Types of Arduino Pins

Pin Type	Description
Power Pins	Provide voltage (5V, 3.3V) and ground (GND).
Digital Pins	Used for input/output (HIGH/LOW signals).
PWM Pins	Provide simulated analog output via pulse-width modulation.
Analog Pins	Read varying voltage values (0-1023 range).
Communication Pins	Used for UART (Serial), I2C, SPI communication.
Special Function Pins	Some pins have multiple functions (e.g., external interrupts, timers).

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🔹 2. Power Pins

Pin	Function
5V	Provides 5V output (for sensors, modules).
3.3V	Provides 3.3V output (for low-voltage components like ESP8266).
GND	Ground (common reference for all components).
VIN	Voltage input (for external power supply, e.g., 7-12V).

📌 Note: Some boards (like Arduino R4 WiFi) support USB-C power delivery with dynamic voltage regulation.

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🔹 3. Digital I/O Pins

• Labeled as D0, D1, D2 … up to D13 (Uno)
• Can be configured as INPUT or OUTPUT using pinMode().
• Reads HIGH (5V) or LOW (0V).

Example: Turn ON an LED

pinMode(7, OUTPUT);   // Set pin 7 as output
digitalWrite(7, HIGH); // Turn LED ON
delay(1000);          // Wait 1 second
digitalWrite(7, LOW);  // Turn LED OFF

📌 Max current per pin: ~40mA (recommended: 20mA).

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🔹 4. PWM Pins (Pulse-Width Modulation)

• Marked with ~ symbol (e.g., ~3, ~5, ~6, ~9, ~10, ~11 on Uno).
• Simulates an analog output (0-255 range) by varying pulse width.
• Used for dimming LEDs, motor speed control.

Example: Fade an LED

analogWrite(9, 128);  // Set brightness to ~50% (0-255 range)

📌 PWM Frequency:

• Uno/Nano: ~490Hz (Pins 5, 6: 980Hz)
• Mega: Varies per pin.

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🔹 5. Analog Input Pins (A0-A5 on Uno)

• Read analog voltages (0V to 5V).
• Return values between 0-1023 (10-bit resolution).

Example: Read a Potentiometer

int sensorValue = analogRead(A0);
float voltage = sensorValue * (5.0 / 1023.0);
Serial.println(voltage);

📌 Tip: Analog pins can also be used as digital pins (pinMode(A0, OUTPUT);).

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🔹 6. Communication Pins

Protocol	Pins Used	Description
UART (Serial)	D0 (RX), D1 (TX)	Used for USB communication (connects to PC).
I2C (Two-Wire)	A4 (SDA), A5 (SCL)	Connects multiple devices (LCD, sensors).
SPI (High-Speed)	D10 (SS), D11 (MOSI), D12 (MISO), D13 (SCK)	Fast communication (SD cards, displays).

📌 Note:

• Arduino R4 WiFi has dedicated hardware I2C (SDA/SCL) on specific pins.
• Use Wire.h for I2C, SPI.h for SPI, and Serial.begin(9600); for UART.

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🔹 7. Special Function Pins

Pin	Function
D2, D3	External Interrupts (for real-time events).
D13	Built-in LED (on many Arduino boards).
RESET	Resets the board when pressed.

Interrupt Example (Button Press)

attachInterrupt(digitalPinToInterrupt(2), myFunction, FALLING);

📌 Useful for: Sensors, rotary encoders, real-time triggers.

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🔹 8. Power Considerations

Feature	Value
Max Pin Current	40mA (Recommended: 20mA)
Max Board Current (5V Regulator)	~500mA (USB) or ~1A (External 9V Supply)
Safe Load for PWM	~20mA (Use MOSFETs for motors)

⚠️ Don’t connect high-power devices directly to Arduino! Use relays, transistors, or MOSFETs.

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🎯 Summary

• Digital Pins: D0-D13 for ON/OFF signals.
• PWM Pins: ~3, ~5, ~6, ~9, ~10, ~11 simulate analog output.
• Analog Pins: A0-A5 read voltage variations (0-1023).
• Power Pins: 5V, 3.3V, VIN, GND provide power.
• Communication Pins: UART, I2C, SPI for external modules.