using ds18b20 for return water temp

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using ds18b20 for return water temp

Postby jap » Thu Sep 24, 2015 10:33 pm

Hi,

I have a OTGW sitting between my boiler and thermostat which is working great. (It's sending the data to my NAS so I have pretty graphs, and there's a tiny python script on the NAS fetching the outside temperature from my neighbour's weather station through Weather Underground and sending it to the OTGW, and the thermostat shows it in its display -- really liking this internet of things thing :) )

I would like to add one thing though: my boiler does not provide the return water temperature. As the OTGW is in the same closet as the boiler, I was thinking of mounting a ds18b20 to the return water pipe and connecting that to one of the GPIOs, and having the OTGW send the return water temperature to the thermostat. I haven't looked at the firmware sources yet, but would it be doable to add that functionality?

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Re: using ds18b20 for return water temp

Postby hvxl » Tue Oct 13, 2015 5:38 pm

The gateway already has the code necessary to do a temperature measurement. Changing that so the value is interpreted as the return water temperature rather than the outside temperature shouldn't be too hard if you're not totally hopeless at programming.

I can't help but wonder why you want this. You indicated you want to send the information to the thermostat. But thermostats generally don't need it to be able to control the room temperature. Some thermostats may have a menu option to report the temperature, but I doubt that you'll use that more than a few times.

Also before you start the work: Are you sure your boiler is unable to produce the value (it returns unknown dataID)? It could also be that your thermostat just doesn't request the data.
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Re: using ds18b20 for return water temp

Postby leander » Sat Feb 06, 2016 8:02 am

I would also like to use a DS18B20 as a sensor attached to the GPIO port to measure the return water temperature.
My Boiler is either not measuring it at all or simply doesn't report it via opentherm. I've already tried sending the AA=28 command to the gateway.

It does not indeed make a whole lot of sense to only show the return temperature on the display of the thermostat.
What I would like to do, is to have the temperature reading sent via mqtt to my broker and from there I can put it in a graph that shows me the delta T.

Unfortunately, my assembler skills are very minimal, so changing the source code of the gateway myself is a bridge to far.

@hvxl, maybe you can consider putting in this functionality as a feature request :roll:
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Re: using ds18b20 for return water temp

Postby blb » Sun Mar 05, 2017 11:41 pm

I just started a new topic about exactly the same, so I deleted it. I would like this feature as well. The reason is My Heater/boiler doesn't provide Return water temperature via Opentherm. I have connected the gateway to my home automation system and I would like to monitor the return water to evaluate the efficiency of my CV installation. The difference between CV water temperature and return water temperature is an indication for the efficiency of the CV installation.
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Re: using ds18b20 for return water temp

Postby rjblake » Mon Mar 13, 2017 2:43 pm

Or look at adding a cheap ESP8266 to do this - plenty of already created projects to do just that (e.g. instructables.com/id/Simple-Example-Ard ... 66DS18B20/ or http://robertoostenveld.nl/arduino-ds18b20/)
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Re: using ds18b20 for return water temp

Postby butyl » Mon Mar 13, 2017 2:45 pm

If you are still interested in replacing "Outside temperature" to "Return water temperature" there are easy and complex way to do it. As hvxl mentioned, there is need to do some changes in the gateway code.
Easiest way to do this is to replace this three parts of source code:
Code: Select all
      goto   MessageID27   ;Data ID 27
      goto   WordResponse   ;Data ID 28

Code: Select all
MessageID27   btfsc   MsgResponse   ;Do not modify a request
      btfss   OutsideTemp   ;Do nothing if no outside temp available
      return
      btfsc   OutsideInvalid
      goto   messageinv
      call   messageack   ;Turn request into acknowledgement
      movfw   outside1
      call   setbyte3
      movfw   outside2
      goto   setbyte4

Code: Select all
#define      outsideval1   valuestorage + 22
#define      outsideval2   valuestorage + 23


by this three parts:

Code: Select all
      goto   WordResponse   ;Data ID 27
      goto   MessageID28   ;Data ID 28

Code: Select all
MessageID28   btfsc   MsgResponse   ;Do not modify a request
      btfss   OutsideTemp   ;Do nothing if no outside temp available
      return
      btfsc   OutsideInvalid
      goto   messageinv
      call   messageack   ;Turn request into acknowledgement
      movfw   outside1
      call   setbyte3
      movfw   outside2
      goto   setbyte4

Code: Select all
#define      outsideval1   valuestorage + 24
#define      outsideval2   valuestorage + 25

Finaly you need just compile it to hex file and upload to the otgw PIC. :D
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Re: using ds18b20 for return water temp

Postby blb » Mon Mar 13, 2017 8:14 pm

rjblake, butyl, thanks for both options, I'll have a look at both.
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