ESP32 poe noise

[korneo]

Hello everyone,

i have a ESP32-POE2 board and I am reading an potentiometer (0-3.3V) value, however there is a(200KHz) ripple on all voltage rails which is not desirable for accurate measurements.

i have already added an 10nF capacitor close to the input, and a bigger one, which does not help unfortunately.

this significant ripple only appears when the poe power supply is connected(HP1820 J9982A), on usb it works fine and all voltage rails are stable(no 200KHz noise)

does anyone know how i can get rid of the ripple and can obtain a stable adc readout?

thanks in advance

[LubOlimex]

Where and how exactly do you measure this noise? Where do you attach your equipment, so we can test in same conditions.

[LubOlimex]

By the way attaching oscilloscope to ESP32-POE2 powered by PoE is risky, ESP32-POE2 is not isolated and it is ground loop risk.

[korneo]

image

The above image was measured on the 3.3V line(as close to the wrovere chip as possible) using a Lecroy ZS1000 active probe while the Poe2 board was powered using the Poe comming from a hp 1820(J9982A) switch.

I suspect the noise is comming from the TX4138 buck converter, however the reason why i do not know.

similair noise is measured on a olimex esp32 poe iso board, however it is not as significant as this one.

[korneo]

Dear Lubolimex from Olimex, has there been any updates regarding this topic? i have used a diffrent poe board from another supplier which solved the issue, however i really like the Olimex boards and would love to use for simmulair applications, which isnt an option unfortunatly.

with kind regards,

Kornei

[LubOlimex]

Lower the driver strength of the GPIO pin responsible for the Ethernet clock.

In hardware revsions prior to revision H, this might be caused by bigger than needed driver strength set by the software on the Ethernet clock pin (GPIO17). Lower the drive strength of the digital output num 17 from the default value 20mA to 5mA. There are usually 4 levels of strength from 0 to 3.

In Arduino this can be done with:

gpio_set_drive_capability((gpio_num_t)GPIO_NUM_17, GPIO_DRIVE_CAP_0);

and also you need to include at top:
#include "driver/gpio.h"

We've also summited it in the ESP32 for Arduino package here, so the fix should be there in next release.