Hello I have written a radiator soft based on ESPHome and everything even works, however something is connected to GPIO 35 of ESP32, see pictures 1 and 2. What could it be? I've given a simple code to read the voltage on the pin, it wiggles, see picture 3 Mill WC Marcin NTC Voltage2.

GPIO 35 on the ESP32 can only act as an input and in my opinion is not connected to anything. This input has no pull-up or pull-down, so you are reading noise.

In the picture you can see that GPIO35 is connected to something (marked with an arrow), but the further signal path cannot be discerned. It looks like the output of an optocoupler.

To fix the note, where is GPIO 35 (perhaps a different GPIO is involved):

I relied on Espressif documentation

@inot You are correct. I posted the wrong pin description and will correct it in a moment. As you can see there are errors in the documentation too

You can see that the factory software is somehow doing a readout of this GPIO. The chip this path goes to is the L2145, I am basing this on this documentation. Code to read GPO 35. Code: text Expand Select all Copy to clipboard - platform: adc pin: GPIO35 name: ${sub_text_devicename} NTC Voltage2 id: ${sub_esphome_name}_adc_sensor2 icon: mdi:flash-outline update_interval: 30s attenuation: 12db #filters: # - multiply: 3.3 filters: - multiply: 0.97 - sliding_window_moving_average: window_size: 15 send_every: 5

It is necessary to trace where the path leads from resistor R15 so that the source of this measurement can be determined.

Which means I have to take the radiator apart.... again... Good.

By the way, take a clearer picture of this section. It is not possible to recognise all the connections.

Mill ESP32 Esphome - what is connected to GPIO35? Fluctuating voltage on a pin

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#1 21745834 09 Nov 2025 02:17

redblue redblue

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Post #1
21745834 09 Nov 2025 02:17

Hello

I have written a radiator soft based on ESPHome and everything even works, however something is connected to GPIO 35 of ESP32, see pictures 1 and 2. What could it be? I've given a simple code to read the voltage on the pin, it wiggles, see picture 3 "Mill WC Marcin NTC Voltage2".

https://github.com/redblue-pkt/mill-esp32
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#2 21746162 09 Nov 2025 13:56

Anonymous Anonymous

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Post #2
21746162 09 Nov 2025 13:56

GPIO 35 on the ESP32 can only act as an input and in my opinion is not connected to anything. This input has no pull-up or pull-down, so you are reading "noise".
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#3 21746195 09 Nov 2025 14:44

inot inot

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Post #3
21746195 09 Nov 2025 14:44

In the picture you can see that GPIO35 is connected to something (marked with an arrow), but the further signal path cannot be discerned. It looks like the output of an optocoupler.

Attachments:

Screenshot 2025-11-09 144009.png Download (736.9 KB)
#4 21746217 09 Nov 2025 15:19

Anonymous Anonymous

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Post #4
21746217 09 Nov 2025 15:19

To fix the note, where is GPIO 35 (perhaps a different GPIO is involved):
#5 21746227 09 Nov 2025 15:32

inot inot

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Post #5
21746227 09 Nov 2025 15:32

I relied on Espressif documentation https://www.mouser.com/datasheet/2/891/esp-wr...uvSwI0_0Nx5cwzem2lSHAdMuyHSrftJtEO5jo4VO9tu_h
#6 21746318 09 Nov 2025 16:46

Anonymous Anonymous

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Post #6
21746318 09 Nov 2025 16:46

@inot You are correct. I posted the wrong pin description and will correct it in a moment. As you can see there are errors in the documentation too
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#7 21746329 09 Nov 2025 16:52

redblue redblue

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21746329 09 Nov 2025 16:52

You can see that the factory software is somehow doing a readout of this GPIO. The chip this path goes to is the L2145, I am basing this on this documentation.

Code to read GPO 35.

  - platform: adc
    pin: GPIO35
    name: ${sub_text_devicename} NTC Voltage2
    id: ${sub_esphome_name}_adc_sensor2
    icon: mdi:flash-outline
    update_interval: 30s
    attenuation: 12db
    #filters:
    #  - multiply: 3.3
    filters:
      - multiply:  0.97
      - sliding_window_moving_average:
          window_size: 15
          send_every: 5

Attachments:

flash_dump_400.bin Download (4 MB)

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#8 21746510 09 Nov 2025 19:22

inot inot

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Post #8
21746510 09 Nov 2025 19:22

It is necessary to trace where the path leads from resistor R15 so that the source of this measurement can be determined.
#9 21746550 09 Nov 2025 19:50

redblue redblue

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Post #9
21746550 09 Nov 2025 19:50

Which means I have to take the radiator apart.... again... Good.
#10 21746590 09 Nov 2025 20:18

inot inot

Level 38
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Post #10
21746590 09 Nov 2025 20:18

By the way, take a clearer picture of this section. It is not possible to recognise all the connections.

Attachments:

Screenshot 2025-11-09 201646.png Download (849.64 KB)
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