Board Errors

❌ Arduino Not Detected by Computer

Symptoms

• “Port not found”
• No COM port appears in Tools → Port
• Upload button does nothing

  Possible causes

• Port not selected correctly
• Board not selected correctly

  How to Fix

  1. Go to:
• Tools → Board → Arduino Uno
• Tools → Port → select the COM port

1. Try a different USB cable
2. Restart the Arduino IDE

❌ Wrong Board Selected

Symptoms

• Upload fails with mysterious errors
• Code worked on another board but not this one

  Possible causes

• Arduino IDE defaults to the wrong board (e.g., Nano, Mega)

  How to Fix

• In the Arduino IDE:
• Tools → Board → Arduino Uno

Syntax Errors (Code Won’t Compile)

❌ Missing Semicolon (;)

Symptoms

• Red error messages
• Errors point to lines that look correct

  Example Error

  int ledPin = 13
  

  Fix

  Add a semicolon:

  int ledPin = 13;
  

  Every Arduino instruction ends with a semicolon.

❌ Misspelled Keywords

Symptoms

• Error: ‘lodop’ was not declared in this scope

  Possible causes

• Arduino is case-sensitive
• Typing mistakes

  Example

  digitalwrite(13, HIGH);
  

  Fix

  Correct capitalization:

  digitalWrite(13, HIGH);
  

❌ Missing or Extra Braces { }

Symptoms

• Error: expected ‘}’ at end of input
• Code compiles halfway

  Why It Happens

• setup() or loop() not closed properly

  Fix

  Ensure matching braces:

void setup()
{
    // code
}

void loop()
{
    // code
}

❌ Using = Instead of ==

Symptoms

• if statements always run or never run

  Example

  if (buttonState = HIGH)
  

  Possible causes

• = assigns a value
• == compares values

  Fix

  if (buttonState == HIGH)
  

❌ Forgetting pinMode()

Symptoms

• LED doesn’t turn on
• Button gives random values

  Possible causes

• Arduino pins default to INPUT

  Fix

  In setup():

  pinMode(13, OUTPUT);
  pinMode(2, INPUT);
  

❌ Wrong Pin Number

Symptoms

• LED or sensor doesn’t respond

  Possible causes

• Code uses a pin, but wire is connected to a different pin

  Fix

• Double-check wiring
• Match code pin numbers to physical pins

❌ Problems with Serial Monitor

Symptoms

• Serial Monitor shows gibberish

  Possible causes

• Serial Monitor speed doesn’t match code

  Fix

  Ensure both match:

  Serial.begin(9600);
  

  Set Serial Monitor to 9600 baud

❌ Serial Monitor Not Open

Symptoms

• Nothing prints

  Fix

• Click Tools → Serial Monitor
• Or press Ctrl + Shift + M

❌ LED Wired Backwards

Symptoms

• LED doesn’t light up

  Possible causes

• LEDs are polarized

  Fix

• Long leg → positive (pin)
• Short leg → GND (Ground)

❌ LED not working

Symptoms

• LED burns out
• Arduino resets randomly

  Fix

  1. Add a 220Ω–330Ω resistor in series with LED
  2. Try a different LED with a resistor in series

❌ Button Issues

Symptoms

• Button reads random HIGH/LOW

  Possible causes

• Input pin is not pulled up or down

  Fix

  Use internal pull-up:

  pinMode(buttonPin, INPUT_PULLUP);
  

❌ Board Powered But Not Running Code

Symptoms

• Power LED is on
• Nothing else works

  Fix

• Re-upload sketch
• Check setup() runs (add a test LED blink)

❌ Putting Code Outside loop() or setup()

Symptoms

• Compile errors

  Fix

  All executable code must be inside:

  void setup() { }
  void loop() { }
  

❌ Code only supposed to Run Once

Symptoms

• Unexpected repeated behavior

  Possible causes

• loop() runs forever
• while() or for() runs forever

  Fix

• setup() → runs once
• loop() → repeats endlessly
• Check conditions inside for() or while() loops are correct