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ESP32 Safety Checklist

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This checklist covers a complete ESP32 hardware build before first power-on.

Electrical Safety

3.3 V Logic

  • All components connected to GPIO pins are verified as 3.3 V tolerant
  • Any 5 V sensor outputs are routed through a level shifter before reaching ESP32 GPIO
  • No GPIO pin is directly connected to a voltage source above 3.3 V
  • Strapping pins (GPIO 0, 2, 12, 15) are accounted for in schematic and will be in correct state at boot

GPIO Limits

  • No single GPIO pin is sourcing or sinking more than 12 mA
  • Total combined GPIO current does not exceed 1200 mA
  • LEDs driven from GPIO have a current-limiting resistor (minimum 220 ohm for 3.3 V rails)
  • All unused GPIO pins set to defined state (INPUT_PULLDOWN or INPUT_PULLUP) in firmware

Grounding

  • All components share a common ground reference
  • No floating ground connections between modules
  • Analog and digital grounds joined at a single point (if using ADC)

No Mains Contact

  • No mains (120 V / 240 V AC) wiring is accessible from the ESP32 side of any relay or MOSFET
  • Relay used provides galvanic isolation between ESP32 circuit and mains load
  • Enclosure prevents accidental contact with any mains-carrying conductor

Power Safety

Regulator and Supply

  • Voltage regulator output verified with multimeter before connecting ESP32 (should read 3.28–3.32 V)
  • Regulator is rated for at least 1.5x the expected maximum current draw
  • Decoupling capacitors placed near ESP32 VCC pin (100 nF ceramic + 10 µF electrolytic)
  • Decoupling capacitors placed near each sensor module VCC pin (100 nF ceramic minimum)

LiPo Battery

  • Battery protection IC (DW01A or equivalent) is present — not just the charger IC
  • Battery polarity verified before connection (LiPo connectors are not polarized by default)
  • Charging current set appropriately (not exceeding C/2 for standard LiPo cells)
  • Battery is not swollen, punctured, or damaged
  • A fuse (500 mA to 1 A) is present on the battery positive lead

MOSFET and Load Switching

  • Logic-level MOSFET confirmed (gate drive sufficient at 3.3 V)
  • Gate resistor (100 to 470 ohm) present in series with GPIO to MOSFET gate
  • Flyback diode present across any relay coil or inductive load (cathode to VCC side)
  • No inductive load switching without snubber or flyback protection

Firmware Safety

Watchdog Timer

  • Hardware or software watchdog enabled for all production code
  • Main loop feeds watchdog regularly (or task watchdog is subscribed)
  • Expected maximum loop time is less than watchdog timeout

Loop Discipline

  • No delay() calls exceeding 100 ms in the main loop (unless intentional)
  • No infinite blocking loops without a timeout or watchdog
  • ISR functions marked with IRAM_ATTR
  • ISR does not call Serial.print, malloc, or I2C/SPI functions

Input Handling

  • Button and switch inputs have debounce logic (software or hardware)
  • Debounce period is at least 20 ms
  • Encoder inputs use interrupt-driven reading or fast polling with Gray code validation
  • All input pins have defined pull-up or pull-down state

Memory

  • Stack size for each FreeRTOS task verified with uxTaskGetStackHighWaterMark during development
  • ESP.getFreeHeap() monitored; minimum free heap does not decrease over time during extended run
  • No unbounded heap allocations in main loop

RF Safety

LoRa / 433 MHz / 2.4 GHz

  • Antenna connected before powering module (operating without antenna can damage PA)
  • Antenna type appropriate for frequency and application
  • Duty cycle compliance verified for operating frequency band (EU 868 MHz: 1% typical)
  • RF module decoupling capacitors placed near module VCC (100 nF + 100 µF)
  • RF trace / antenna wire kept away from digital switching signals

WiFi / Bluetooth

  • ADC1 used for analog readings (ADC2 conflicts with WiFi)
  • WiFi TX power set appropriately for range needed (higher power not always better)
  • Bluetooth and WiFi coexistence mode configured if using both simultaneously

Physical Safety

Wiring and Assembly

  • All solder joints inspected under magnification — shiny, concave, cone-shaped
  • No solder bridges between adjacent pins
  • No cold solder joints (dull, grainy, or uneven appearance)
  • No stray wire strands that could cause shorts
  • All wire connections rated for expected current

Insulation and Strain Relief

  • No bare wire terminations exposed where they could contact other conductors
  • Heat shrink or electrical tape applied to all single-conductor bare ends
  • Power cables secured with zip tie or tape at entry point to PCB — no tension on solder joints
  • Battery wires have strain relief at connector and at PCB

Enclosure

  • Enclosure material is non-conductive or all conductive surfaces are grounded
  • Ventilation present if enclosure will contain a charging LiPo or high-current regulator
  • Enclosure provides mechanical protection against accidental short circuits
  • Mounting hardware (screws, standoffs) does not contact PCB traces or components

First Power-On Sequence

  • Verify power supply output voltage with multimeter before connecting ESP32
  • Connect ESP32 last (after all other wiring is verified)
  • Monitor serial output during first boot for error messages
  • Verify ESP.getFreeHeap() is reasonable (>100 KB for typical sketches)
  • Check for unexpected heat from any component within 30 seconds of power-on
  • Verify expected LED blink or serial message indicating firmware is running
  • Disconnect power immediately if any component becomes hot to the touch

See Also