ESPHome calculating ntc/adc wrong?!

ESPHome
1

Hi all,
I think I’m losing my mind.

I had a test circuit with an ESP32 and a 10kOhm NTC that worked fine. So I had a PCB made to attach a couple more NTCs, confirmed with the old configuration that it still worked and started adapting the code for more sensors (of course I didn’t make a backup…).
Now the ESP32 reads the correct voltage, calculates the correct resistance and reports a temperature that’s not even remotely close to correct. I don’t understand what is going on.

grafik
grafik808×166 5.63 KB

I have verified the voltage and resistance with a multimeter and manually calculating it gives me the expected value of ~21 °C. Reference resistor is also actually 10kOhm.

Here is my current configuration:

esphome:
  name: esphome-web-6662b4
  friendly_name: ESP32 Thermometer Warmwasser
  min_version: 2025.9.0
  name_add_mac_suffix: false

esp32:
  variant: esp32
  framework:
    type: esp-idf

# Enable logging
logger:

# Enable Home Assistant API
api:

# Allow Over-The-Air updates
ota:
- platform: esphome

wifi:
  ssid: !secret wifi_ssid
  password: !secret wifi_password
  manual_ip:
    # Set this to the IP of the ESP
    static_ip: 192.168.1.205
    # Set this to the IP address of the router. Often ends with .1
    gateway: 192.168.1.1
    # The subnet of the network. 255.255.255.0 works for most home networks.
    subnet: 255.255.255.0
  # Enable fallback hotspot (captive portal) in case wifi connection fails
captive_portal:

switch:
  - platform: gpio
    pin: GPIO32
    id: ntc_vcc_5
   
interval:
  - interval: 1s
    then:
    - switch.turn_on: ntc_vcc_5
    - component.update: ntc_5
    - switch.turn_off: ntc_vcc_5

sensor:
  - platform: ntc
    sensor: ntc_5
    calibration:
      b_constant: 3590
      reference_temperature: 25°C
      reference_resistance: 10kOhm
    name: NTC Temperature 5

  # Example source sensors:
  - platform: resistance
    id: ntc_r_5
    sensor: ntc_5
    configuration: DOWNSTREAM
    resistor: 10kOhm
    name: Resistance Sensor 5

# ADC sensors
  - platform: adc
    id: ntc_5
    pin: GPIO33
    attenuation: auto
    update_interval: 1s
    filters:
    - sliding_window_moving_average:
        window_size: 60
        send_every: 30
        send_first_at: 30

Help? :frowning:

Once again I wish I could just slap down some C-code.

2

What’s the point here?

3

That’s to avoid self-heating. Taken from the official documentation: NTC Sensor - ESPHome - Smart Home Made Simple
1s interval is of course only for testing, so you don’t have to wait forever.

But it shows the same behavior with constantly activated pins.

4

should be sensor: ntc_r_5

5

sensor should be using ntc_r_5

2 Likes
6

Aww man… now I feel really dumb. Thanks a lot to you two for catching that.

Guess I shouldn’t be fiddeling with ESPHome after 10 pm in the future.

1 Like
7

Still better than 2am… :wink: