ESP32 Dev Board LED Connection?

[Xylopyrographer]

I've picked up a number of 38 pin ESP32 dev boards from AliExpress & Amazon. The physical layout of the boards are identical. Near the header pin marked G2, there is a single red LED. Does anyone know, is this LED connected to a GPIO pin and if so, which one? The LED flickers initially during power-up but then goes out, inferring it's under GPIO control. The canonical ESP 32 Espressif reference design for DevKit C v4 shows a single LED connected to +5V Vdd. So if these were the same, it would be on all the time when powered by the USB port, which it is not.

Attempts to gain this information from the online stores has been fruitless.

Of course the complete schematic for these would be a bonus!

Reference links:
Amazon: https://www.amazon.ca/gp/product/B086ZM ... UTF8&psc=1
AliExpress: https://www.aliexpress.com/item/1005001 ... 4c4davQglx

ESP32DevBrdLED.jpg (118.28 KiB) Viewed 14254 times

[felmue]

Hello @Xylopyrographer

just guessing here, maybe it's connected to GPIO1/U0TXD? That would at least explain the flickering during power up. You could try to run a sketch with `Serial.println()` debug statements and if the LED flickers then too, that would confirm it.

Thanks
Felix

[Xylopyrographer]

Ah. There you go. Running the basic Blink program driving IO1 does indeed control the LED.

Of course that makes the serial monitor port kinda useless... Unless I flash the LED at 115200 baud !

Thanks Felix.

[shenanigami]

Hey @felmue

can you explain what is the connection between GPIO1/U0TXD and powerup? I want to understand how you've made your guess.

[Xylopyrographer]

When powered up, the ESP sends a bunch of information out to the USB port via UART0, which is connected to the Serial/USB bridge chip.

On this particular board, the designers chose to put an LED on the TXD line of UART0, I suppose to let the user know when the ESP32 is sending data.

This was confirmed by loading the standard Blink sketch to the device, driving GPIO pin 1 (which is the default TXD pin for UART0).

Hope that clears it up.

[shenanigami]

Thanks, @ Xylopyrographer! Your response helped