A few weeks ago I run into a strange problem — when I was playing with ESP8266 and Arduino Libraries, suddenly my program stopped working. Random characters were appearing on UART (Arduino Serial). Also it was almost not possible to flash the chip via the UART. “Ok, I blew up the UART somehow,” I thought. Today, the problem appeared again, so I replaced the module with a new one. After few minutes, the I observed the same strange behavior – random characters appeared again. What?

Because I didn’t touch the module, I started inspecting what’s going on. I revisited all the connections and all the Dupont cables. Everything was fine. As a last desperate try I lowered the upload speed from 921600 Bd/s to 57600 Bd/s. The chip came alive!

I haven’t inspect properly, what is the cause, yet. It seems to me like there might be an interference on a the cheap Chinese Dupont cables during high speed upload and the uploaded program can get corrupted (and so the ESP might be stuck in a loop of fault handlers).

Next time, when you think you blew your ESP8266, try lowering upload speed first!