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Topic: Yet another thermostat project (Read 2812 times) previous topic - next topic


Jan 31, 2012, 02:18 am Last Edit: Feb 11, 2012, 07:45 pm by Celelibi Reason: 1

As the title say, I'd like to automatically control the heat of my flat.
This will include some remote bluetooth temperature sensors and stuff, but that's not what I'm most worried about. :)

Actually, I'm not a hardware guy, and I don't really know how I could handle the radiators (convection heaters).

A few constraints about the main radiator (I'll tackle others later):
- I can't control its power supply directly: I only have a big electric cable going directly from the wall to the radiator without any plug.
- The main control is a wheel, but since the wheel is on the wall side of the convector, I can't control it with a servo.

Here are a few pictures of my radiator.

A front view:

An overall view when down its fixations:

Two top views of the wheel with a ruler to get an idea of the size:

Notice the wall fixation that may be useful:

Focus on the wheel itself with a ruler for the size:

Wall fixation sysem:

I think the only way to control the radiator is to use some kind of motor and plastic wheel to make it turn.
And here start the troubles for me:
- What kind of motor should I use? DC? Stepper? motoreductor?
- Since this system will rely on plastic "grip" to make the radiator wheel turn, how do I know when I should stop the motor? Must I use a rotation sensor? If yes, what kind of rotation sensor?

And then, depending on the previous answers, what kind of board should I use?

Thanks for your futures replies.

[EDIT: I added the pictures]


Well, I think a stepper would be fine, since I could control the speed and relative position. I juste have no idea how I could detect the radiator's wheel is at its extrem position.


Without a picture, I have to make some assumptions, but I think that this is going to be tricky. Depending on the wheel, you may be able to fit some sort of end stop sensor, but as space seems to be an issue, I dont think this is possible.

Disclaimer: Mains is dangerous and can (and will) kill given the oppertunity*

I think personally it would be easier to just get a new heater that you can "modify" and would probably cost less or similiar to the parts you need to interface with the existing units.

For example, get one with a wheel that you can modify the casing of to allow fitting of a servo or even the rotary encoder from an old mouse.
This would allow for all the existing safety features of the heater to function - and if you are experienced or have guidance, even relay control the heater for on/off as well.

The only thing I would add is that self controlled heaters can also be dangerous, as even low power heaters can burn things in certain conditions - so make sure you leave the internal cut off thermostat connected at all times, just to be safe - never hurts to have a failsafe in case anything goes wrong with your controller.

* I feel I always like to say this (if only to remind myself)


As I previously said, I can't take a picture.
But what I did is a schema of the situation (not really precise since I'm not at home right now).
Hope this will make things more clear.

Moreover, the wheel has some small holes in it and can rotate 270° max. That looks perfect for a servo... if there's enough room...
Or... These holes (I discovered yesterday) could be used as a rotary encoder or so.

(I definitely need a camera... I think I'll buy one soon.)

Well, I know mains is dangerous, and I'd like to avoid dealing with it. ^^

Replacing the current heater or opening it could be a solution, but I rent my flat and do not want to take the risk to fuck up anything that's not mine.
And since there is no plug, I would feel uncomfortable trying to replace the convector.


270 degrees of movement is a bit much for a servo, as most only do around 180 degrees.

If the wheel is fully exposed, then you should be able to use the holes for mounting, but it looks like you dont have room to use it as a rotary encoder, and seeing as the heater blocks one side of it - that doesnt look like an (easy) option.

This is why I suggested just ignoring this heater and using your own one... if nothing else you are then free to modify it how you want - replacing the wheel with a gear/stepper combo or maybe gear/servo.

If you could attach a gear wheel to the wheel on the heater, you are sorted though... you could drive the gear with a geared stepper motor and use a potentiometer on another (larger) gear for position feedback, as the pot gear needs to rotate less than 180 degrees for the 270 of the wheel.... not sure if you have enough room to fit it though, and you would still need to attach it to the heater.

dont know if this is any help... but these are some more of my ramblings.


Feb 11, 2012, 07:52 pm Last Edit: Feb 11, 2012, 07:57 pm by Celelibi Reason: 1
I updated the first message to add the pictures.

I think the holes could be used to attach a gear and make it turn with a motor. What do you think about that?

If I can attach a gear to the wheel I no longer need a feedback of the rotation since there can't be any "loss of rotation".

Another option I've been given is to open the white box on the wall and place (where the electric cable goes to the wall) and insert a kind of regulator. But, well... Playing with mains scare me a bit.

Buying a new heater is the option I keep last since I do not want to buy one for every room. ^^


If you can space your heater another 2cm off of the wall, you probably could make a simple servo powered controller for the thermostat adjustment knob if the knob is easy to turn. Below is a simple setup where a larger spool attached to the servo turns a smaller shaft in a blind. The servo 180 deg rotation would rotate the small shaft ~2.5 times. 

Google forum search: Use Google Search box in upper right side of this page.
Why I like my 2005 Rio Yellow Honda S2000  https://www.youtube.com/watch?v=pWjMvrkUqX0


I think the holes could be used to attach a gear and make it turn with a motor.

Take the control wheel off and replace it with a gear. Fit a second gear to a 720 degree servo, job done. If you need to get the heater further from the wall, some wooden battens behind the heater supports would do it.

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