Voltage and Power Traps

• 3.3V vs 5V logic mixing damages boards — ESP32 is 3.3V, Uno is 5V, level shifter required
• USB provides max 500mA — not enough for motors, servos, or many LEDs
• Never power motors from Arduino 5V pin — use external supply with common ground
• Brown-out causes random resets — looks like code bugs, actually insufficient power
• Decoupling capacitors (0.1µF) near sensor power pins — reduces noise-related glitches

Wiring Mistakes

• Floating inputs read random values — always use pullup or pulldown resistor
• All components must share common ground — separate grounds = nothing works
• Long wires pick up noise — keep analog sensor wires short
• LEDs need current limiting resistors — direct connection burns LED and pin
• Reversed polarity destroys components — double-check before powering on

Pin Conflicts

• RX/TX pins (0, 1) conflict with Serial — avoid for GPIO when using Serial Monitor
• Some pins have special functions — check board pinout for I2C, SPI, interrupt-capable pins
• PWM only on pins marked with ~ — analogWrite() on wrong pin does nothing
• Internal pullup available — INPUT_PULLUP eliminates external resistor for buttons

Timing Traps

• delay() blocks everything — nothing else runs, no input reading, no interrupts serviced
• millis() for non-blocking timing — compare against last action time
• millis() overflows after ~50 days — use subtraction: millis() - lastTime >= interval
• Interrupts for time-critical events — attachInterrupt() responds immediately

Memory Constraints

• Uno has only 2KB RAM — large arrays fail silently with weird behavior
• F() macro keeps strings in flash — Serial.println(F("text")) saves RAM
• PROGMEM for constant arrays — keeps data out of RAM
• String class fragments heap — prefer char arrays for stability

Serial Debugging

• Baud rate must match — mismatch shows garbage, not an obvious error
• Serial.begin() required in setup — output before this goes nowhere
• Serial printing slows execution — remove or reduce for production code

Upload Problems

• Wrong board selected — uploads but doesn't run correctly
• Serial Monitor holds port — close before uploading
• USB cable might be power-only — some cheap cables don't carry data
• Bootloader corrupted — reflash using another Arduino as ISP

Sensor Communication

• I2C devices share bus — check for address conflicts with scanner sketch
• 5V sensors on 3.3V boards give wrong readings or damage — check operating voltage
• SPI needs separate CS per device — can't share chip select lines