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Suddenly I was unable to reflash a pair of ESP8266 boards (one nodeMCU, and one Wemos D1).

I had been using those for testing/developing a remote temperature and humidity sensor station with Arduino (C++) and MicroPython for over a year, but yesterday they didn’t work any more. The error was

gabriel@gear:~/.local/bin$ ./esptool.py --port /dev/ttyUSB0 --baud 115200 erase_flash
esptool.py v3.3
Serial port /dev/ttyUSB0
Connecting......................................

A fatal error occurred: Failed to connect to Espressif device: No serial data received.
For troubleshooting steps visit: https://docs.espressif.com/projects/esptool/en/latest/troubleshooting.html

I tried every trick and hack found on the Internet, to no avail (I tried esptool.py from 1.0 through 3.3, grounded I/O pin GPIO0, etc.)

Did I brick my boards forever?

Peter Mortensen
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1 Answers1

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You wouldn't believe it: the problem was the boards were still connected to the DHT11 sensor while reflashing, something I've been doing from day 1.

Out of frustration, I pulled out the DHT11 sensor, leaving the board unconnected to anything and it finally worked:

./esptool.py --port /dev/ttyUSB0 --baud 115200 erase_flash

Output

esptool.py v3.3
Serial port /dev/ttyUSB0
Connecting....
Detecting chip type... Unsupported detection protocol, switching and trying again...
Connecting....
Detecting chip type... ESP8266
Chip is ESP8266EX
Features: WiFi
Crystal is 26MHz
MAC: 5c:cf:7f:3d:10:36
Uploading stub...
Running stub...
Stub running...
Erasing flash (this may take a while)...
Chip erase completed successfully in 10.0s
Hard resetting via RTS pin...

Well, the DHT11 data pin was connected to D3, which is GPIO0.

Peter Mortensen
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