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Hello,

I would like to connect a ESP-12 on my otgw, due to limitations and possibilities to get get a cable from boiler to raspberry pi with domoticz.
I have the usb otgw and moved to another house.

Though I dont want to solder new components, Im not so good in that.
I can power the ESP-12 external, but no signals coming trough from otgw. If I using a TTL cable, in OTmonitor I see correct values.
If I connect the ESP-12 external and only connect RX to TX and TX to RX, I dont get any values. It does connect via OTmonitor / port 23 but no values in the log.

Is that because I dont use the ground pin from the otgw?
If so, can I connect the ground from the external psu (phone charger with modified usb cable to pin cables) to the ground of of the otgw and also connect to the esp-12 module? Or should I use somehow the gpio ground pin ?

For serial data to be exchanged between two devices, they need to have their grounds connected. But beware: The ESP-12 uses signals at 3.3V, while the OTGW works with 5V. The ESP-12 may tolerate the higher level without getting damaged, but 3.3V is not high enough for the OTGW. So, unless you put a level-shifter in between, you won't be able to send any data from the ESP-12 to the OTGW. If you're lucky, then if the 5V signals don't blow your ESP-12, the other direction may work.

I don't understand your setup well enough to know what the difference is between the "ground from the external psu" and "the gpio ground pin".