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Opentherm connected to ESP8266

PostPosted: Thu Feb 04, 2016 7:25 pm
by bryan241
Hi All,

I've connected an esp8266 to the opentherm gateway which functions as a serial to wifi bridge.
This works perfectly for 24 hours now.

My question is more related to powering the esp.
the esp requires max 240ma (3v3). I have a level shifter in between the esp and the opentherm gateway.

Is it possible to power the esp from the internal opentherm power supply?
The 7805 needs to be cooled for sure, but can the transformer deliver enough power for the opentherm gateway and the esp?



Re: Opentherm connected to ESP8266

PostPosted: Fri Feb 05, 2016 1:48 pm
by adijk

Re: Opentherm connected to ESP8266

PostPosted: Fri Feb 05, 2016 1:57 pm
by Bwired
can you post a small schematic (with partsnr) how you connected the ESP?
would be great!

Re: Opentherm connected to ESP8266

PostPosted: Fri Feb 05, 2016 8:07 pm
by bryan241
Thanks for the great reference post. (why didn't I find this while searching through the old posts?)
I've ordered a replacement transformer and dc-dc converter.

For testing Ive used a chinese 220v to 5v power supply, like this one: ... 1932592389
Not exactly the same because my model is not sold anymore, probably for a reason...

I'm using ... rTxDU9fRdg as the esp.
loaded with serial bridge firmware. tx connected to rx on otgw and rx to tx.
Connected grounds to each other and connected +5 from the chinese power adapter to the esp.
Works great for 36 hours now.


Re: Opentherm connected to ESP8266

PostPosted: Fri Apr 29, 2016 10:53 am
by stoffel67
I have connected a ESP8266 to my OTGW too.
( I replaced the 7805 with RECOM R-78E5.0-0.5, the ESP8266 is powered with LF33CV,
and between PIC and ESP8266 I use a Levelshifter for the data lines)

I see all the replies from the OTGW in the Log
but when I try to "send" Free Format command" like "PR=B"
the command is sent( in the Log),
but I do not get repsonse from the PIC in the Log
so, it seems nothing is sent to the PIC...?

I have tested the ESP8266 with Connection to PC( WLAN and USB-TTL), and it works perfect in both directions...

Any hints where to search?


Re: Opentherm connected to ESP8266

PostPosted: Tue Apr 25, 2017 5:52 pm
by vadimber

If you firstly connect to power OTGW and after that connect ESP to OTGW it works, but there are some side effects...

When I use OTGW with upgraded parts for supply ESP8266 (serial bridge ... 0.0.V0PEGu with 5V->3.3V on board converter), Otmonitor regularly receives "E" "SE" errors from OTGW is such setup, see log below in "PS=1" mode. There are no any errors when I directly connect OTGW to my Notebook throw USB cable

log sample:
11:41:15.283083 E
11:41:15.503945 E
11:41:15.621174 E
11:41:15.742293 E
11:41:15.859102 E
11:41:16.015367 E
11:41:16.058062 SE
11:41:16.187271 E
11:41:16.303038 E
11:41:16.419744 E
11:41:16.537263 E
11:41:16.658378 E

Do you have any ideas?

Thank you!