Strange REPL issue

All ESP8266 boards running MicroPython.
Official boards are the Adafruit Huzzah and Feather boards.
Target audience: MicroPython users with an ESP8266 board.
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rpi_nerd
Posts: 24
Joined: Sat Jul 29, 2017 2:05 pm

Strange REPL issue

Post by rpi_nerd » Tue Dec 17, 2019 6:08 pm

I got another WeMos D1 board yesterday. I flashed the latest version of MicroPython today. I was able to get to the REPL prompt, but I couldn't send any characters, just receive. I found that by plugging it in but not hitting reset I can send characters just fine. I flashed an older version of the firmware and got the same symptoms.

rpi_nerd
Posts: 24
Joined: Sat Jul 29, 2017 2:05 pm

Re: Strange REPL issue

Post by rpi_nerd » Sun Jan 05, 2020 5:16 pm

I dug into the issue further. After I hit the reset button there's no activity between the TX pin of the CH340/RX pin of the ESP8266. So it's either the CH340 chip that's the issue or if the ESP8266 is pulling the line down. My next step is to remove the 470 ohm resistor in series and isolate the ESP8266 chip and determine which component is problematic when I get a chance. The replacement board that I got from the same vender is also acting up in the same way.

rpi_nerd
Posts: 24
Joined: Sat Jul 29, 2017 2:05 pm

Re: Strange REPL issue

Post by rpi_nerd » Mon Jan 06, 2020 4:47 pm

Today I removed the rx/tx series resistors and hooked up another USB to serial adapter. Same symptoms so it looked like the ESP8266 module was at fault, but I noticed something. After I hit the reset button on the module and tried to type on the console, the activity light on my USB to serial adapter wasn't lighting up as if nothing was being sent to the adapter at all. I restarted PuTTY and everything was working again. I tried another serial console problem, and didn't have any issues.

tl;dr it wasn't either the CH340 or the ESP8266 module, it's some strange issue with PuTTY.

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