5V tolerant I O? - mhightower83/Arduino-ESP8266-misc GitHub Wiki

Good discussion here:

• Is ESP8266 I/O really 5V tolerant?
• Espressif's site: What is the voltage tolerance of GPIOs of ESP chips?
  • The voltage tolerance is 3.6 V. If the voltage exceeds 3.6 V, please add a voltage divider to protect GPIO pins from damage.

When considering ringing for the input case, I prefer to play it safe and incorporate the level conversion in the resistor selection. They are needed anyway to reduce ringing.

Research References:

Find a FET for those level translator circuits. Also related, Espressif's Hardware Design Guideline, Figure 1-10b. ESP8266EX UART SWAP provides an example circuit to deal with issues that can occur with MCUs connected to GPIO15.

• What can I replace a BSS138 N-Channel MOSFET with?
  • Picking FET for level translator circuit
    • For easy soldering TN0702 looks promissing
  • FET Alternative Replacement
    • Adafruit: The Great Search: BSS138 Dual N-Channel FET Alternative Replacement