Confused about flashing ESP32 + MH-Z19B for the first time

ESPHome
1

The Problem

So this is my first time attempting to flash an ESP32 and I’m struggling to get it to flash with a connected MH-Z19B.

I’m at the part where I’ve saved my YAML file, and I’m clicking “Install”, but I run into errors that I cannot seem to get past no matter what I try.

When I try to flash it with the sensor connected to the ESP32, I get the following error:

...
INFO Successfully compiled program.
esptool.py v4.6.2
Serial port /dev/ttyUSB1
Connecting......................................
ERROR Running command failed: Failed to connect to ESP32: Download mode successfully detected, but getting no sync reply: The serial TX path seems to be down.
For troubleshooting steps visit: https://docs.espressif.com/projects/esptool/en/latest/troubleshooting.html
ERROR Please try running esptool.py --before default_reset --after hard_reset --baud 460800 --port /dev/ttyUSB1 --chip esp32 write_flash -z --flash_size detect 0x10000 /data/build/co2-sensor/.pioenvs/co2-sensor/firmware.bin 0x1000 /data/build/co2-sensor/.pioenvs/co2-sensor/bootloader.bin 0x8000 /data/build/co2-sensor/.pioenvs/co2-sensor/partitions.bin 0xe000 /data/cache/platformio/packages/framework-arduinoespressif32/tools/partitions/boot_app0.bin locally.
INFO Upload with baud rate 460800 failed. Trying again with baud rate 115200.
esptool.py v4.6.2
Serial port /dev/ttyUSB1
Connecting......................................
ERROR Running command failed: Failed to connect to ESP32: Download mode successfully detected, but getting no sync reply: The serial TX path seems to be down.
For troubleshooting steps visit: https://docs.espressif.com/projects/esptool/en/latest/troubleshooting.html
ERROR Please try running esptool.py --before default_reset --after hard_reset --baud 115200 --port /dev/ttyUSB1 --chip esp32 write_flash -z --flash_size detect 0x10000 /data/build/co2-sensor/.pioenvs/co2-sensor/firmware.bin 0x1000 /data/build/co2-sensor/.pioenvs/co2-sensor/bootloader.bin 0x8000 /data/build/co2-sensor/.pioenvs/co2-sensor/partitions.bin 0xe000 /data/cache/platformio/packages/framework-arduinoespressif32/tools/partitions/boot_app0.bin locally.

The troubleshooting page mentions:

This implies a problem with the TX line running from the host to the ESP device. Double-check your board or breadboard circuit for any problems.

Which I have tried to look into, and I cannot see anything wrong. I have the correct pins connected, and I’ve tried numerous (4 pinned) micro-USB cables to rule out a cable issue.

Additional Information

My YAML config is:

esphome:
  name: co2-sensor
  friendly_name: CO2 Sensor

esp32:
  board: esp32dev
  framework:
    type: arduino

uart:
  rx_pin: GPIO3
  tx_pin: GPIO1
  baud_rate: 9600

sensor:
  - platform: mhz19
    co2:
      name: "MH-Z19 CO2 Value"
    temperature:
      name: "MH-Z19 Temperature"
    update_interval: 60s
    automatic_baseline_calibration: false

# Enable logging
logger:

# Enable Home Assistant API
api:
  encryption:
    key: "***"

ota:
  password: "***"

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

captive_portal:

Pin Connections

MH-Z19B GND ↔ ESP32 GND
MH-Z19B Vin ↔ ESP32 V5
MH-Z19B TX ↔ ESP32 RX0
MH-Z19B RX ↔ ESP32 TX0

(I have also tried swapping TX/RX as I read in the ESPHome docs that these are flipped regularly)

Parts

This is the exact ESP32 I ordered: https://www.aliexpress.com/item/1005005970816555.html?spm=a2g0o.order_list.order_list_main.16.b3ea1802AiEKEo

This is the exact MH-Z19B I ordered: https://www.aliexpress.com/item/4000212024923.html?spm=a2g0o.order_list.order_list_main.22.b3ea1802AiEKEo

These are the exact jumper wires I’m using: https://www.aliexpress.com/item/4000203371860.html?spm=a2g0o.order_list.order_list_main.28.b3ea1802AiEKEo

Thank you in advance for any help :pray:

2

As I understand it, GPIO1 and GPIO3 are generally used by the usb port. So you cannot flash over usb while you have something else attached to to them. You are better off using 16 and 17, which normally also has an UART. If you must use 1 and 3, then you need to disconnect those, flash through usb, and then connect them. All updates you can then flash OTA via wifi.

2 Likes
3

You were spot on! GPIO 16 and 17 worked like a charm!

So strange that there’s no error or anything useful in the logs or documentation (that I could find) to hint that using GPIO 1 and 3 while flashing doesn’t work.

This is probably just common knowledge for people with experience. But for people with no experience just getting into this, it’s quite confusing.

Thanks for the help Edwin! Much appreciated :slight_smile:

1 Like