2026

Use old ESP board as Serial Adapter

I wanted to flash a Sonoff NSPanel the other day and my FTDI started doing weird things, brownouts and garbage on the line. Rather than digging through the drawer for a better one, plan B : the NodeMCU sitting right there.

It has a CH340 or CP2102 onboard, a 5V rail, and a 3.3V regulator very likely better than the tiny thing on your FTDI board. Which is exactly what an ESP32 pulling current mid-flash needs.

Two things to note :

1. Connect EN to GND to disable the ESP8266.
2. TX goes to TX, RX goes to RX. The silkscreen labels the ESP8266’s pins, so the crossover is already done on the PCB.

NodeMCU  ->  target
GND      ->  GND
3.3V     ->  3.3V
TX       ->  TX
RX       ->  RX

No DTR here. Short GPIO0 to GND yourself to enter download mode, and tell esptool not to bother resetting anything :

esptool.py --port /dev/cu.usbserial-0001 --baud 115200 \
  --before no_reset --after no_reset write-flash 0x0 tasmota32-nspanel.factory.bin

(write-flash is esptool v5, use write_flash on older versions.)

Same wiring works for an Arduino Pro Mini, press RESET by hand when the IDE says Uploading.

Hope it saves you a trip to the parts drawer !