After reading 100’s of forums on the NodeMCU Zombie issue after deepsleep wake-up, and myself spending many, many late nights on this problem, it seems I resolved my own issue…….hope it could be of help to others too.
I also struggled with the instable state that sometimes occur after deepsleep. I also experienced the semi-brick state occasionally where a factory standard AT firmware flash was required to start over.
I tried different firmware. Tried all the best practices on pull-up resistors. Tried WiFi disconnect and some funny proposals on random delays before activating deep sleep…..nothing was truly working.
What did however work on my setup: ESP8266 -01 connected via FT232RL USB To Serial 232 running ESPlorer, flashing with ESP8266Flasher NodeMCU 0.9.5 was:
Dump the USB tool’s 3.3V supply and used a 12V Pb-Acid regulated with LM1117 3.3v Regulator with 10uF cap on 3.3V line. It seems like these chips are EXTREMELY sensitive to VCC during startup. I am sure many other supplies could also work, I just opted for the most stable and clean supply I had at hand. After seeing the stability improvement I verified by swapping back to USB’s 3.3V supply and the zombie state re-appeared. Using a clean 3.3CV supply I have cycled through 3000 Wake-up, post to internet, deepsleep routines since last night without missing a single beat .
Hope this can help to allow us to spend time on more important issues.