ESP32-WROOM-32 module

Question

Hi everyone, I just got the ESP32-WROOM-32 module and I’m trying to use its onboard LED + some external LEDs in a project. But I’m confused about which pins are safe to use for LED blinking and why some are behaving strangely. What I’ve Done / Setup Powered the module with a regulated 3.3 V supply. Used the built-in LED pin (as per the datasheet) and wired another external LED with resistor to a GPIO pin. Used Arduino / platform of choice to blink the LEDs for testing. The built-in LED works fine when I flash a simple blink sketch. But when I use certain GPIO pins (that I thought were usable), the LED either doesn’t blink, or it blinks very dimly / flickers. Sometimes if I pick a pin that’s also used for “boot mode / strapping” or flash interface, the module won’t boot or the sketch upload fails. I believe some pins are strapping pins (or have fixed roles at boot) on the ESP32 so they can’t be used freely. Ensured LED wiring is correct, resistor is in line, grounding is proper. Which GPIO pins on the ESP32-WROOM-32 have you found reliable for external LEDs (output mode) without affecting boot or causing conflicts? Are there specific “bad / restricted” pins I should completely avoid for LED driving (because of boot/flash usage or other strapping)? Thanks!

Aimee0 · Answer

Hello, Could you please confirm if you are using WIZnet products? For questions regarding ESP products, we kindly recommend using the Espressif forum.