an idea of toshiba official RBC-AMT31 schematic

[cambridge2009]

https://github.com/burrocargado/toshiba-aircon-mqtt-bridge/blob/master/schematic/KiCad/remote_controller-Toshiba%20Remote%20Controller.png

please take a look at this, here is a toshiba official schematic of remote controller (RBC-AMT31) on Github, from which you can get 5V power form AB line, and TX RX to MCU, might be a goot way to remove external power supply on your board

[issalig]

Great! I will take a look at it.
AFAIK, I connected the ESP8266 to some 5V pad on the remote PCB but it drained too much power and the remote could not power on.
Anyway, I will check the scheme, maybe I was connecting it in another place.

Also, in this discussion #5 (comment) there is a circuit by @muxa and also other one borrowed from @bbqkees

[cambridge2009]

there is an other picture in same folder which shows how to make 3.3V on H_TAP line from offical schematic.
Get power from H_TAP should be ok
https://github.com/burrocargado/toshiba-aircon-mqtt-bridge/blob/master/schematic/KiCad/wireless_controller-Wireless%20Controller.png