arduino networked thermostat project

[linux-works]

starting a new project, revising a many-times solved idea, but perhaps doing your own tstat is a rite of passage, of sorts



planning to have it be xbee networked and multi-zone aware.  will have an rf oled remote with the same screen but on a handheld unit (that controls other things, too).

led is RGB; temp sensor is ds81b20 but may change to something else.  there will be a webserver interface, eventually, too (html and json/REST).

[pickle9000]

Can it detect if a room is occupied (PIR)?

[linux-works]

was thinking of trying a new sensor:

http://www.amazon.com/Geeetech-Infrared-proximity-compatible-Arduino/dp/B00AMC1V2C

I've used this thing before, and might consider it again:

http://www.amazon.com/gp/product/B00IMOSEJA

for the oled screen, it needs to be off unless somone is nearby.

as for other sensor inputs, the rest would have to send xbee messages to be part of the system.  of course, its all diy and open source so the protocol will be public and actually easy to implement.  I'll write interfaces for whatever I need and will add more as I find time or get new sensors to try out.

I'm doing some early r/d on some motorized 'vanes' (flaps) that come in metal heating pipes (6-9" size sample is what I've seen).  we want to remote control the zones' airflow using these settable vanes and that meant I had to put together a main controller for the simple stuff, first.

the interesting part is whether some kind of rf (xbee pro?) is going to be good enough to give reliable comms between the controller on the wall and the pipes in the attic or basement or wherever.  wired-ethernet with PoE is a possibility but I would love to find an rf packet solution that can be used where wired-ethernet is not an option or preference.

[pickle9000]

For a sensor try this, has a range of 20 feet.

http://www.ebay.ca/itm/Useful-HC-SR501-Infrared-PIR-Motion-Sensor-Module-for-Arduino-Raspberry-pi-TOUS-/381328013865?pt=LH_DefaultDomain_0&hash=item58c8ebba29

When it comes to the flow control remember that changing one will change the entire heating system. Tuning a system so you get the heat / cold you want is normal. Having said that you can run it and then see how good they are and then offer a suggestion.

[linux-works]

balancing the system is going to be a trick.  but first steps first; allow control of physical things and measurements.  then worry about HOW to do it all in software, later (lol).

[pickle9000]

One simple way to do the control is to sense the temp of the room that has flow control. Once the temp has been reached lower the flow for that area, the remaining areas will heat (or cool) faster and so on. Of course if you are sensing room occupancy then only heat that room, should save a fair bit of energy. Checking room temp was often used for pre-computer era tuning. 

As for control would not a simple rf link (low cost) work? You could use a single channel and for ones too distant have a closer one relay a command. That would allow for a wide and more reliable communications.

http://www.ebay.ca/itm/Enduring-1X-NRF24L01-2-4GHz-Wireless-RF-Transceiver-Module-For-Arduino-HFUS-/171845849253?pt=LH_DefaultDomain_0&hash=item2802cf90a5

For forced hot air a 3d printed and motorized vent cover with a simplified controller would be a simple install.

Excellent project, I look forward to seeing how you make out.

[linux-works]

I'm very fussy about reliability; security, etc.  I want NO part of someone's system getting hacked or toyed with or some bug allowing a bad combo of modes.  so I'm really unsure if wireless, of any affordable kind, can really pass muster for this kind of use.  I think I'll go slowly and start off with wired PoE for power and data.  that will be for the motors and controllers out neare the pipes and ducts.  if you have to run power, its not much harder to run ethernet cable and send power over that.   I know wired ethernet and can trust it.  but I'll keep an eye out for a wired replacement, if there is such a thing.  not interested in wifi; simply don't trust it for this application and companies that do, are fools.

as for room presence, I'll start off letting people select WHERE they want the hvac to take effect.  once that works and works for a while in the real world, I'll add more smarts.  much better to start simple, do things well and add features over time as you perfect and study it.  I don't want to create something that is rushed too fast to market (even if its just a DIY).

I'll update the thread as I make progress.

thx for the comments

[pickle9000]

When it comes to security wired or wireless it has to be in your software. If you do that you will have little to no problems. I come from the days of autotel when if you talked conversations are heard. Using coded transmissions are the only way to go and they need to change often. One trick we always used was to use the number of letters in a word as a key. The number 3 was red but so was tan blue was 4 no one ever figured out the system.

 Today we can reprogram a fob (car key remote) after every use, makes them very hard to crack. If the reprogramming fails then it reverts to the last good code. The beauty of single channel comms like this is that you can have thousands of control points. The hard part is not having things talk at the same time.

You are not wrong when it comes to security and automation gear. It not only helps with malicious acts but also keeps the system running smoothly by introducing checks, and self tests. I use GSM modems to send text messages from automation systems, very reliable system. The messages depend on what the customer wants but may include operation changes, failures and so on.