Im curious as to wether this is possible or not being a total begineer when it comes to arduino and most electronics and programming. I want to know if it is possible.
The project is the following
Changing a wired weather compensation unit to a wireless one if possible?
The current sensor is wired 12k ntc on the outside of the building wired back to a boiler were dependant on the outside temperature the boiler flow temperature modulates to suit. ie the hotter it is outside the cooler the the flow temperature would be.
Is it possible for arduino to send a signal like this wirelessly or not.
Any help would be greatly appreciated even if you just come out and say no its not possible
The arduino can read the temperature via the sensor and control the wireless. The only unknown is what is the distance and nature of the building in between.
I would think that the bigger issue is how the boiler uses the value of the thermistor. The outdoor reset thermistor on my boiler is connected to a 24v ac signal and the magic processing to determine outlet water temperatures is not known. You might be able to get a wireless control to work if you transmitted the thermistor value, and then recreated it at the boiler with a digital potentiometer and fed the recreated resistance to the boiler controller.
A bigger question is whether your modification would void the warranty for your boiler and void your house and liability insurances.
Making one Arduino send data to another Arduino is fairly easy. Making the process as reliable as your existing arrangement AND PROVING IT will not be easy.
You would need to present a signal that the existing control system "sees" as a resistor with variable voltage across it. The existing sensor must have a voltage across it for it to work. You would need to replicate this signal.
To use one arduino for send and another for receive to replace 15m of cable, with inherently risk, would seem not worthwhile.
The warranty issue wouldn't be an issue, its out of warranty and its what I spend my days fixing anyways :-*
So today Ive found out that the output voltage of the boiler to the ntc is 5v.
The 15m was just a rough guess and 30m would be better. Sometimes its not practical to run a cable through someones house for a WC sensor although the property would benefit from having WC.
If the project is feasible I would like to press on with it. If someone would point be in the right direction for some reading material that would he good.
In the United States, both Honeywell and Beckett sell wireless outdoor reset boiler controls, so it can be done. A Google search should get you some links. These controls are meant to be integrated with their exisiting boiler controllers which are often add on controllers for older boilers, but you may get some ideas.
Are you trying to interface with a modulating/condensing boiler with an integrated control?
Determining the end to end resistance required and the number of steps will be your first task. I would break this project into the variable resistor piece and the wireless/ntc piece. The wireless transmission of a resistor value is pretty straightforward, and I would focus on getting the boiler responding to the digital resistance and making sure you had the correct sensitivity and failure mode issues worked out. What is the variable resistance of the ntc sensor over the temperature range of interest?
As the others have stated, you are getting into some potentially deep water with this project, but the existing boiler controller may be currently able to handle all sorts of weirdness with the outdoor reset values.
Thank you for your helpful reply. The boiler has a direct connection for the wc sensor. Two terminals are wired to the outdoor sensor. The boiler reads the resistance from the sensor and then onboard software modulates to suit.
Yes I have a honeywell evo system currently which has the option of an outdoor sensor and yet they dont support the feature in the uk. They also dont currently support opentherm in the uk yet. Although an Opentherm bridge is coming I believe.
Also would it be worth buying the arduino starter set? Which digital pot would be capable of giving a 12k resistance? The boiler in question gives a chart available but doesnt give a resistance compared to temperature but if I remember correctly 12k is measured at 21 degrees C
Also would it be worth buying the arduino starter set?
This is not a good starter project. I would recommend that you bring the wired wc sensor to your boiler, get it working Figure out the reset curves and operating parameters for the output water temperatures, and decide if you can improve your comfort or lower your costs. Much will depend upon the size of your boiler, and how it is matched to the heat emitters (radiant panels, baseboards, in floor tubing,etc) in your house. Not all emitters can take advantage of running lower water temperature.
I wold be very comfortable with my existing boiler controller and all the fine details of how to set the temperature limits and water temperatures based on outdoor temperatures before I tackled doing it wireless and digitally. If you really can't wire the outdoor sensor to the boiler, you can use a standard potentiometer/rheostat, wire it to the terminals, and find some settings to use for a very warm or cold day. Monitor your outlet temperatures and see if you can stay warm with different outlet temperatures.
