arduino

## 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