Reading from UART timed out at byte 0!

ozizka · March 12, 2025, 2:51pm

I am new to esphome and trying to get work mh-z19e on esp32-c3 supermini. I successfully set up esp32, communication with home assistant seem ok, I double checked uart connection, everything seems fine, but i am still receiving this error:

Reading from UART timed out at byte 0!
Reading data from MHZ19 failed!

Any help for me? Thanks…

Logs


INFO ESPHome 2025.2.2
INFO Reading configuration /config/esphome/esphome-web-4e61bc.yaml...
INFO Starting log output from 192.168.1.209 using esphome API
INFO Successfully connected to esphome-web-4e61bc @ 192.168.1.209 in 0.015s
INFO Successful handshake with esphome-web-4e61bc @ 192.168.1.209 in 1.246s
[15:36:53][I][app:100]: ESPHome version 2025.2.2 compiled on Mar 12 2025, 15:33:03
[15:36:53][C][wifi:600]: WiFi:
[15:36:53][C][wifi:428]:   Local MAC: A0:85:E3:4E:61:BC
[15:36:53][C][wifi:433]:   SSID: [redacted]
[15:36:53][C][wifi:436]:   IP Address: 192.168.1.209
[15:36:53][C][wifi:439]:   BSSID: [redacted]
[15:36:53][C][wifi:441]:   Hostname: 'esphome-web-4e61bc'
[15:36:53][C][wifi:443]:   Signal strength: -65 dB ▂▄▆█
[15:36:53][C][wifi:447]:   Channel: 3
[15:36:53][C][wifi:448]:   Subnet: 255.255.255.0
[15:36:53][C][wifi:449]:   Gateway: 192.168.1.1
[15:36:53][C][wifi:450]:   DNS1: 192.168.1.1
[15:36:53][C][wifi:451]:   DNS2: 178.17.0.11
[15:36:53][C][logger:177]: Logger:
[15:36:53][C][logger:178]:   Max Level: DEBUG
[15:36:53][C][logger:179]:   Initial Level: DEBUG
[15:36:53][C][logger:181]:   Log Baud Rate: 115200
[15:36:53][C][logger:182]:   Hardware UART: USB_SERIAL_JTAG
[15:36:53][C][uart.idf:159]: UART Bus 0:
[15:36:53][C][uart.idf:160]:   TX Pin: GPIO21
[15:36:53][C][uart.idf:161]:   RX Pin: GPIO20
[15:36:53][C][uart.idf:163]:   RX Buffer Size: 256
[15:36:53][C][uart.idf:165]:   Baud Rate: 9600 baud
[15:36:53][C][mhz19:104]: MH-Z19:
[15:36:53][C][mhz19:105]:     Device Class: 'carbon_dioxide'
[15:36:53][C][mhz19:115]:   Warmup time: 75 s
[15:36:53][C][esphome.ota:073]: Over-The-Air updates:
[15:36:53][C][api:140]: API Server:
[15:36:58][D][api:103]: Accepted 192.168.1.149
[15:36:58][D][api.connection:1446]: Home Assistant 2025.3.2 (192.168.1.149): Connected successfully
[15:36:58][D][api:103]: Accepted 192.168.1.149
[15:36:58][D][api.connection:1446]: ESPHome Logs 2025.2.2 (192.168.1.149): Connected successfully
[15:37:39][W][mhz19:037]: MHZ19 warming up, 18 s left
[15:37:44][I][safe_mode:041]: Boot seems successful; resetting boot loop counter
[15:37:44][D][esp32.preferences:114]: Saving 1 preferences to flash...
[15:37:44][D][esp32.preferences:142]: Saving 1 preferences to flash: 0 cached, 1 written, 0 failed
[15:38:39][D][uart_debug:114]: <<< 47:0C:DE:47:0C:DE:47:0C:DE:47:0C:DE:FF:FF:FF:FF:FF:FF:FF:FF:FF:69:C4:1F:07:0C:DE:FF:FF:FF:FF:FF:FF:FF:FF:FF:29:84:1F
[15:38:39][E][uart:015]: Reading from UART timed out at byte 0!
[15:38:39][W][mhz19:044]: Reading data from MHZ19 failed!
[15:38:39][W][component:237]: Component mhz19.sensor took a long time for an operation (120 ms).
[15:38:39][W][component:238]: Components should block for at most 30 ms.
[15:38:39][D][uart_debug:114]: >>> FF:01:86:00:00:00:00:00:79
[15:39:39][E][uart:015]: Reading from UART timed out at byte 0!
[15:39:39][W][mhz19:044]: Reading data from MHZ19 failed!
[15:39:39][W][component:237]: Component mhz19.sensor took a long time for an operation (116 ms).
[15:39:39][W][component:238]: Components should block for at most 30 ms.
[15:39:39][D][uart_debug:114]: >>> FF:01:86:00:00:00:00:00:79

neel-m · March 12, 2025, 3:06pm

You need to include your config and you need to use code tags to make it readable.

This is also worth reading:

Just a guess, since there is no config, but it looks like you might have both uart debug and the mhz sensor connected to the same uart. So the debug might be eating all the bytes before the sensor can see them.

ozizka · March 14, 2025, 10:21pm

Thanks for reply and information.

Here is a actual log and config:

Config:

esphome:
  name: esphome-web-4e61bc
  friendly_name: Senzor
  min_version: 2024.11.0
  name_add_mac_suffix: false

esp32:
  board: esp32-c3-devkitm-1
  framework:
    type: esp-idf

# Enable logger
logger:

# Enable Home Assistant API
api:

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

wifi:
  ssid: !secret wifi_ssid
  password: !secret wifi_password
  output_power: 8.5

uart:
  tx_pin: 21
  rx_pin: 20
  baud_rate: 9600

sensor:
  - platform: mhz19
    co2:
      name: MH-Z19 CO2 Value
    temperature:
      name: MH-Z19 Temperature

Log:

INFO ESPHome 2025.2.2
INFO Reading configuration /config/esphome/esphome-web-4e61bc.yaml...
INFO Starting log output from 192.168.1.209 using esphome API
INFO Successfully connected to esphome-web-4e61bc @ 192.168.1.209 in 0.051s
INFO Successful handshake with esphome-web-4e61bc @ 192.168.1.209 in 0.022s
[16:27:54][I][app:100]: ESPHome version 2025.2.2 compiled on Mar 13 2025, 23:35:02
[16:27:54][C][wifi:600]: WiFi:
[16:27:54][C][wifi:428]:   Local MAC: A0:85:E3:4E:61:BC
[16:27:54][C][wifi:433]:   SSID: [redacted]
[16:27:54][C][wifi:436]:   IP Address: 192.168.1.209
[16:27:54][C][wifi:439]:   BSSID: [redacted]
[16:27:54][C][wifi:441]:   Hostname: 'esphome-web-4e61bc'
[16:27:54][C][wifi:443]:   Signal strength: -62 dB ▂▄▆█
[16:27:54][C][wifi:447]:   Channel: 3
[16:27:54][C][wifi:448]:   Subnet: 255.255.255.0
[16:27:54][C][wifi:449]:   Gateway: 192.168.1.1
[16:27:54][C][wifi:450]:   DNS1: 192.168.1.1
[16:27:54][C][wifi:451]:   DNS2: 178.17.0.11
[16:27:54][C][logger:177]: Logger:
[16:27:54][C][logger:178]:   Max Level: DEBUG
[16:27:54][C][logger:179]:   Initial Level: DEBUG
[16:27:54][C][logger:181]:   Log Baud Rate: 115200
[16:27:54][C][logger:182]:   Hardware UART: USB_SERIAL_JTAG
[16:27:54][C][uart.idf:159]: UART Bus 0:
[16:27:54][C][uart.idf:160]:   TX Pin: GPIO21
[16:27:54][C][uart.idf:161]:   RX Pin: GPIO20
[16:27:54][C][uart.idf:163]:   RX Buffer Size: 256
[16:27:54][C][uart.idf:165]:   Baud Rate: 9600 baud
[16:27:54][C][uart.idf:166]:   Data Bits: 8
[16:27:54][C][uart.idf:167]:   Parity: NONE
[16:27:54][C][uart.idf:168]:   Stop bits: 1
[16:27:54][C][mhz19:104]: MH-Z19:
[16:27:54][C][mhz19:105]:   CO2 'MH-Z19 CO2 Value'
[16:27:54][C][mhz19:105]:     Device Class: 'carbon_dioxide'
[16:27:54][C][mhz19:105]:     State Class: 'measurement'
[16:27:54][C][mhz19:105]:     Unit of Measurement: 'ppm'
[16:27:54][C][mhz19:105]:     Accuracy Decimals: 0
[16:27:54][C][mhz19:105]:     Icon: 'mdi:molecule-co2'
[16:27:54][C][mhz19:106]:   Temperature 'MH-Z19 Temperature'
[16:27:54][C][mhz19:106]:     Device Class: 'temperature'
[16:27:54][C][mhz19:106]:     State Class: 'measurement'
[16:27:54][C][mhz19:106]:     Unit of Measurement: '°C'
[16:27:54][C][mhz19:106]:     Accuracy Decimals: 0
[16:27:54][C][mhz19:115]:   Warmup time: 75 s
[16:27:54][C][mdns:116]: mDNS:
[16:27:54][C][mdns:117]:   Hostname: esphome-web-4e61bc
[16:27:54][C][esphome.ota:073]: Over-The-Air updates:
[16:27:54][C][esphome.ota:074]:   Address: esphome-web-4e61bc.local:3232
[16:27:54][C][esphome.ota:075]:   Version: 2
[16:27:54][C][safe_mode:018]: Safe Mode:
[16:27:54][C][safe_mode:019]:   Boot considered successful after 60 seconds
[16:27:54][C][safe_mode:021]:   Invoke after 10 boot attempts
[16:27:54][C][safe_mode:022]:   Remain in safe mode for 300 seconds
[16:27:54][C][api:140]: API Server:
[16:27:54][C][api:141]:   Address: esphome-web-4e61bc.local:6053
[16:27:54][C][api:145]:   Using noise encryption: NO
[16:28:10][W][mhz19:037]: MHZ19 warming up, 37 s left
[16:28:33][I][safe_mode:041]: Boot seems successful; resetting boot loop counter
[16:28:33][D][esp32.preferences:114]: Saving 1 preferences to flash...
[16:28:33][D][esp32.preferences:142]: Saving 1 preferences to flash: 0 cached, 1 written, 0 failed
[16:29:10][E][uart:015]: Reading from UART timed out at byte 0!
[16:29:10][W][mhz19:044]: Reading data from MHZ19 failed!
[16:29:10][W][component:237]: Component mhz19.sensor took a long time for an operation (115 ms).
[16:29:10][W][component:238]: Components should block for at most 30 ms.

neel-m · March 15, 2025, 1:44am

Your new log is not at the same level of debug as the first one.

I would set the log level to very verbose to see if that provides more insight.

This from the first log, seems to indicate there is a debug print on the logger, which could have been consuming the bytes before the mhz component could read them. Your current config doesn’t show you adding a debug statement, but does appear to show the UART component generating an error.

This appears to be the code generating the error:

github.com/esphome/esphome

esphome/components/uart/uart_component.cpp

7679c716b

#include "uart_component.h"

namespace esphome {
namespace uart {

static const char *const TAG = "uart";

bool UARTComponent::check_read_timeout_(size_t len) {
  if (this->available() >= int(len))
    return true;

  uint32_t start_time = millis();
  while (this->available() < int(len)) {
    if (millis() - start_time > 100) {
      ESP_LOGE(TAG, "Reading from UART timed out at byte %u!", this->available());
      return false;
    }
    yield();
  }
  return true;

This file has been truncated. show original

It will wait up to 100ms for the amount of data to show up.

This is the MH-Z19 code:

github.com/esphome/esphome

esphome/components/mhz19/mhz19.cpp

7679c716b

#include "mhz19.h"
#include "esphome/core/log.h"

#include <cinttypes>

namespace esphome {
namespace mhz19 {

static const char *const TAG = "mhz19";
static const uint8_t MHZ19_REQUEST_LENGTH = 8;
static const uint8_t MHZ19_RESPONSE_LENGTH = 9;
static const uint8_t MHZ19_COMMAND_GET_PPM[] = {0xFF, 0x01, 0x86, 0x00, 0x00, 0x00, 0x00, 0x00};
static const uint8_t MHZ19_COMMAND_ABC_ENABLE[] = {0xFF, 0x01, 0x79, 0xA0, 0x00, 0x00, 0x00, 0x00};
static const uint8_t MHZ19_COMMAND_ABC_DISABLE[] = {0xFF, 0x01, 0x79, 0x00, 0x00, 0x00, 0x00, 0x00};
static const uint8_t MHZ19_COMMAND_CALIBRATE_ZERO[] = {0xFF, 0x01, 0x87, 0x00, 0x00, 0x00, 0x00, 0x00};

uint8_t mhz19_checksum(const uint8_t *command) {
  uint8_t sum = 0;
  for (uint8_t i = 1; i < MHZ19_REQUEST_LENGTH; i++) {
    sum += command[i];

This file has been truncated. show original

line 44 is what reports the error.

Line 89-101 are the main code:

first clear the UART buffer of previous stuff
send command to the sensor
wait for a response

This goes back to esphome/esphome/components/uart/uart_component_esp_idf.cpp at 7679c716b31a0cf79859383dc984e79b3ddf37dc · esphome/esphome · GitHub
line 204 is where it is waiting

My reading of the code and error message is that the MH-Z19 component is waiting for data that does not show up in time. There are more reasons for this to not work than there are for it to work.

It appears that these boards are particularly fussy and others have had issues with esphome.

github.com/esphome/issues

MHZ19 won't connect

opened 11:53AM - 04 Nov 19 UTC

closed 08:02AM - 28 May 21 UTC

dedepene

integration: mhz19 integration: sensor stale

**Operating environment/Installation (Hass.io/Docker/pip/etc.):** hassio add-…on **ESP (ESP32/ESP8266, Board/Sonoff):** NodeMCU, ESP32 **Affected component:** https://esphome.io/components/sensor/mhz19.html **Description of problem:** The CO2 sensor won't connect on a variety of controllers - Nodemcus and ESP32. The very same sensor works fine on just this one NodeMCU with the exacts same settings across the board. Super weird - how do I even begin to troubleshoot? **Problem-relevant YAML-configuration entries:** ``` esphome: name: office platform: ESP8266 board: nodemcuv2 wifi: ssid: "xxx" password: "xxx" # Enable logging logger: # Enable Home Assistant API api: ota: uart: rx_pin: GPIO1 tx_pin: GPIO3 baud_rate: 9600 sensor: - platform: mhz19 co2: name: "Office CO2 Value" temperature: name: "Office Temperature" update_interval: 60s automatic_baseline_calibration: false i2c: sda: 4 scl: 5 scan: True apds9960: address: 0x39 update_interval: 60s binary_sensor: - platform: apds9960 direction: UP name: "APDS960 Up Movement" #filters: # - delayed_off: 1500ms - platform: apds9960 direction: down name: "APDS960 Down Movement" #filters: # - delayed_off: 1500ms - platform: apds9960 direction: left name: "APDS960 Left Movement" #filters: # - delayed_off: 1500ms - platform: apds9960 direction: right name: "APDS960 Right Movement" #filters: # - delayed_off: 1500ms switch: - platform: restart name: "Office Nodemcu Restart" ``` **Logs (if applicable):** ``` [13:50:08][I][app:100]: ESPHome version 1.14.2 compiled on Nov 4 2019, 12:32:03 [13:50:08][C][wifi:409]: WiFi: [13:50:08][C][wifi:277]: SSID: [redacted] [13:50:08][C][wifi:278]: IP Address: 192.168.1.144 [13:50:08][C][wifi:280]: BSSID: [redacted] [13:50:08][C][wifi:281]: Hostname: 'office' [13:50:08][C][wifi:285]: Signal strength: -58 dB ▂▄▆█ [13:50:08][C][wifi:289]: Channel: 1 [13:50:08][C][wifi:290]: Subnet: 255.255.255.0 [13:50:08][C][wifi:291]: Gateway: 192.168.1.1 [13:50:08][C][wifi:292]: DNS1: 54.93.173.153 [13:50:08][C][wifi:293]: DNS2: 46.166.189.68 [13:50:08][C][i2c:028]: I2C Bus: [13:50:08][C][i2c:029]: SDA Pin: GPIO4 [13:50:08][C][i2c:030]: SCL Pin: GPIO5 [13:50:08][C][i2c:031]: Frequency: 50000 Hz [13:50:08][I][i2c:033]: Scanning i2c bus for active devices... [13:50:08][I][i2c:040]: Found i2c device at address 0x39 [13:50:09][C][uart:145]: UART Bus: [13:50:09][C][uart:147]: TX Pin: GPIO3 [13:50:09][C][uart:150]: RX Pin: GPIO1 [13:50:09][C][uart:152]: Baud Rate: 9600 baud [13:50:09][C][uart:153]: Stop bits: 1 [13:50:09][C][uart:157]: Using software serial [13:50:09][C][logger:175]: Logger: [13:50:09][C][logger:176]: Level: DEBUG [13:50:09][C][logger:177]: Log Baud Rate: 115200 [13:50:09][C][logger:178]: Hardware UART: UART0 [13:50:09][C][mhz19:094]: MH-Z19: [13:50:09][C][mhz19:095]: CO2 'Office CO2 Value' [13:50:09][C][mhz19:095]: Unit of Measurement: 'ppm' [13:50:09][C][mhz19:095]: Accuracy Decimals: 0 [13:50:09][C][mhz19:095]: Icon: 'mdi:periodic-table-co2' [13:50:09][C][mhz19:096]: Temperature 'Office Temperature' [13:50:09][C][mhz19:096]: Unit of Measurement: '°C' [13:50:09][C][mhz19:096]: Accuracy Decimals: 0 [13:50:09][C][mhz19:096]: Icon: 'mdi:thermometer' [13:50:09][C][mhz19:102]: Automatic baseline calibration disabled on boot [13:50:09][C][apds9960:124]: APDS9960: [13:50:09][C][apds9960:125]: Address: 0x39 [13:50:09][C][apds9960:127]: Update Interval: 60.0s [13:50:09][C][restart:021]: Restart Switch 'Office Nodemcu Restart' [13:50:09][C][restart:021]: Icon: 'mdi:restart' [13:50:09][C][ota:029]: Over-The-Air Updates: [13:50:09][C][ota:030]: Address: office.local:8266 [13:50:09][C][api:095]: API Server: [13:50:09][C][api:096]: Address: office.local:6053 [13:50:20][E][uart:240]: Reading from UART timed out at byte 0! [13:50:20][W][mhz19:034]: Reading data from MHZ19 failed! [13:51:20][E][uart:240]: Reading from UART timed out at byte 0! [13:51:20][W][mhz19:034]: Reading data from MHZ19 failed! [13:51:31][D][apds9960:282]: Got gesture RIGHT [13:51:31][D][binary_sensor:036]: 'APDS960 Right Movement': Sending state ON [13:51:31][D][binary_sensor:036]: 'APDS960 Right Movement': Sending state OFF ``` **Additional information and things you've tried:** Again, the same sensor, with the exact same settings and wiring will work on just one nodemcu board (Amica), on every other board it fails to connect via UART?! Here's the log from the nodemcu I was lucky with: ``` [13:57:06][I][app:100]: ESPHome version 1.14.2 compiled on Nov 4 2019, 10:39:12 [13:57:06][C][wifi:409]: WiFi: [13:57:06][C][wifi:277]: SSID: [redacted] [13:57:06][C][wifi:278]: IP Address: 192.168.1.228 [13:57:06][C][wifi:280]: BSSID: [redacted] [13:57:06][C][wifi:281]: Hostname: 'load_cell' [13:57:06][C][wifi:285]: Signal strength: -65 dB ▂▄▆█ [13:57:06][C][wifi:289]: Channel: 1 [13:57:06][C][wifi:290]: Subnet: 255.255.255.0 [13:57:06][C][wifi:291]: Gateway: 192.168.1.1 [13:57:06][C][wifi:292]: DNS1: 54.93.173.153 [13:57:06][C][wifi:293]: DNS2: 46.166.189.68 [13:57:06][C][uart:145]: UART Bus: [13:57:06][C][uart:147]: TX Pin: GPIO3 [13:57:06][C][uart:150]: RX Pin: GPIO1 [13:57:06][C][uart:152]: Baud Rate: 9600 baud [13:57:06][C][uart:153]: Stop bits: 1 [13:57:06][C][uart:157]: Using software serial [13:57:06][C][logger:175]: Logger: [13:57:06][C][logger:176]: Level: DEBUG [13:57:06][C][logger:177]: Log Baud Rate: 115200 [13:57:06][C][logger:178]: Hardware UART: UART0 [13:57:06][C][mhz19:094]: MH-Z19: [13:57:06][C][mhz19:095]: CO2 'Kid Room CO2 Value' [13:57:06][C][mhz19:095]: Unit of Measurement: 'ppm' [13:57:06][C][mhz19:095]: Accuracy Decimals: 0 [13:57:06][C][mhz19:095]: Icon: 'mdi:periodic-table-co2' [13:57:06][C][mhz19:096]: Temperature 'Kid Room Temperature' [13:57:06][C][mhz19:096]: Unit of Measurement: '°C' [13:57:06](Message skipped because it was too big to fit in TCP buffer - This is only cosmetic) [13:57:06](Message skipped because it was too big to fit in TCP buffer - This is only cosmetic) [13:57:06](Message skipped because it was too big to fit in TCP buffer - This is only cosmetic) [13:57:06](Message skipped because it was too big to fit in TCP buffer - This is only cosmetic) [13:57:06](Message skipped because it was too big to fit in TCP buffer - This is only cosmetic) [13:57:06][C][api:095]: API Server: [13:57:06][C][api:096]: Address: load_cell.local:6053 [13:57:38][D][mhz19:057]: MHZ19 Received CO₂=529ppm Temperature=22°C Status=0x00 [13:57:38][D][sensor:092]: 'Kid Room CO2 Value': Sending state 529.00000 ppm with 0 decimals of accuracy [13:57:38][D][sensor:092]: 'Kid Room Temperature': Sending state 22.00000 °C with 0 decimals of accuracy ```

Some have had success with Tasmota, others probably gave up and got a better sensor.

ozizka · March 15, 2025, 7:58am

Hello.
Thank you very much for the detailed answer. I’ll try different sensor. If you are interested I tried to adjust the log level and re-enabled debug, but I don’t see anything interesting in log:

INFO ESPHome 2025.2.2
INFO Reading configuration /config/esphome/esphome-web-4e61bc.yaml...
INFO Starting log output from 192.168.1.209 using esphome API
INFO Successfully connected to esphome-web-4e61bc @ 192.168.1.209 in 0.015s
INFO Successful handshake with esphome-web-4e61bc @ 192.168.1.209 in 0.072s
[08:52:27][I][app:100]: ESPHome version 2025.2.2 compiled on Mar 15 2025, 08:43:31
[08:52:27][C][wifi:600]: WiFi:
[08:52:27][C][wifi:428]:   Local MAC: A0:85:E3:4E:61:BC
[08:52:27][C][wifi:433]:   SSID: [redacted]
[08:52:27][C][wifi:436]:   IP Address: 192.168.1.209
[08:52:27][C][wifi:439]:   BSSID: [redacted]
[08:52:27][C][wifi:441]:   Hostname: 'esphome-web-4e61bc'
[08:52:27][C][wifi:443]:   Signal strength: -62 dB ▂▄▆█
[08:52:27][V][wifi:445]:   Priority: 0.0
[08:52:27][C][wifi:447]:   Channel: 3
[08:52:27][C][wifi:448]:   Subnet: 255.255.255.0
[08:52:27][C][wifi:449]:   Gateway: 192.168.1.1
[08:52:27][C][wifi:450]:   DNS1: 192.168.1.1
[08:52:27][C][wifi:451]:   DNS2: 178.17.0.11
[08:52:27][C][logger:177]: Logger:
[08:52:27][C][logger:178]:   Max Level: VERY_VERBOSE
[08:52:27][C][logger:179]:   Initial Level: VERY_VERBOSE
[08:52:27][C][logger:181]:   Log Baud Rate: 115200
[08:52:27][C][logger:182]:   Hardware UART: USB_SERIAL_JTAG
[08:52:27][C][uart.idf:159]: UART Bus 0:
[08:52:27][C][uart.idf:160]:   TX Pin: GPIO21
[08:52:27][C][uart.idf:161]:   RX Pin: GPIO20
[08:52:27][C][uart.idf:163]:   RX Buffer Size: 256
[08:52:27][C][uart.idf:165]:   Baud Rate: 9600 baud
[08:52:27][C][uart.idf:166]:   Data Bits: 8
[08:52:27][C][uart.idf:167]:   Parity: NONE
[08:52:27][C][uart.idf:168]:   Stop bits: 1
[08:52:27][C][mhz19:104]: MH-Z19:
[08:52:27][C][mhz19:105]:   CO2 'MH-Z19 CO2 Value'
[08:52:27][C][mhz19:105]:     Device Class: 'carbon_dioxide'
[08:52:27][C][mhz19:105]:     State Class: 'measurement'
[08:52:27][C][mhz19:105]:     Unit of Measurement: 'ppm'
[08:52:27][C][mhz19:105]:     Accuracy Decimals: 0
[08:52:27][C][mhz19:105]:     Icon: 'mdi:molecule-co2'
[08:52:27][C][mhz19:106]:   Temperature 'MH-Z19 Temperature'
[08:52:27][C][mhz19:106]:     Device Class: 'temperature'
[08:52:27][C][mhz19:106]:     State Class: 'measurement'
[08:52:27][C][mhz19:106]:     Unit of Measurement: '°C'
[08:52:27][C][mhz19:106]:     Accuracy Decimals: 0
[08:52:27][C][mhz19:115]:   Warmup time: 75 s
[08:52:27][C][mdns:116]: mDNS:
[08:52:27][C][mdns:117]:   Hostname: esphome-web-4e61bc
[08:52:27][V][mdns:118]:   Services:
[08:52:27][V][mdns:120]:   - _esphomelib, _tcp, 6053
[08:52:27][V][mdns:122]:     TXT: friendly_name = Senzor
[08:52:27][V][mdns:122]:     TXT: version = 2025.2.2
[08:52:27][V][mdns:122]:     TXT: mac = a085e34e61bc
[08:52:27][V][mdns:122]:     TXT: platform = ESP32
[08:52:27][V][mdns:122]:     TXT: board = esp32-c3-devkitm-1
[08:52:27][V][mdns:122]:     TXT: network = wifi
[08:52:27][C][esphome.ota:073]: Over-The-Air updates:
[08:52:27][C][esphome.ota:074]:   Address: esphome-web-4e61bc.local:3232
[08:52:27][C][esphome.ota:075]:   Version: 2
[08:52:27][C][safe_mode:018]: Safe Mode:
[08:52:27][C][safe_mode:019]:   Boot considered successful after 60 seconds
[08:52:27][C][safe_mode:021]:   Invoke after 10 boot attempts
[08:52:27][C][safe_mode:022]:   Remain in safe mode for 300 seconds
[08:52:27][C][api:140]: API Server:
[08:52:27][C][api:141]:   Address: esphome-web-4e61bc.local:6053
[08:52:27][C][api:145]:   Using noise encryption: NO
[08:52:42][VV][api.service:697]: on_ping_request: PingRequest {}
[08:52:42][VV][api.service:043]: send_ping_response: PingResponse {}
[08:52:51][VV][scheduler:225]: Running interval '' with interval=60000 last_execution=168743 (now=228745)
[08:52:55][VV][scheduler:225]: Running interval 'update' with interval=60000 last_execution=172480 (now=232485)
[08:52:55][VV][uart.idf:237]:     Flushing...
[08:52:55][E][uart:015]: Reading from UART timed out at byte 0!
[08:52:55][W][mhz19:044]: Reading data from MHZ19 failed!
[08:52:55][W][component:237]: Component mhz19.sensor took a long time for an operation (114 ms).
[08:52:55][W][component:238]: Components should block for at most 30 ms.
[08:52:55][D][uart_debug:114]: >>> FF:01:86:00:00:00:00:00:79
[08:53:22][VV][api.service:697]: on_ping_request: PingRequest {}
[08:53:22][VV][api.service:043]: send_ping_response: PingResponse {}
[08:53:27][VV][api.connection:133]: Sending keepalive PING...
[08:53:27][VV][api.service:037]: send_ping_request: PingRequest {}
[08:53:27][VV][api.service:706]: on_ping_response: PingResponse {}

neel-m · March 15, 2025, 4:10pm

This makes it clearer.

The problem appears to be a not so good design of the component. The log shows the MH-Z19 answering with 9 bytes, but the answer comes after the component gave up waiting for the answer. The simple solution is likely to increase the timeout.

There are several ways to do this. The easiest is probably just wait for there to be the 9 bytes it is expecting.

Line 89-101 are the main code:

first clear the UART buffer of previous stuff
send command to the sensor
ADD wait for the correct number of bytes to be available
wait for a response

It is a reasonably simple change if you already know how to modify an existing component.

clone/copy the folder containing the code (I liked the GitHub repo above)
add it as an external component in your YAML
modify one of the logging statements (hello world) do you know it is using your code
make the change

The better fix would be to query the sensor before you need the data, but I am unaware of a good way to do that only before you need the data. The other way is to change the code to periodically query the sensor (use loop() and some additional code to only check every so often) so it always has a value and only publish it when required.