I've been doing something similar for the past couple of months. At present the setup only extends to my workshop (for testing). Currently I am using a single UNO for control which reads various sensor states, including light level and temperature/humidity, plus some door (reed relay) and IR movement sensors. The arduino reads the state and sends messages to some software ( currently Python 2.7 under Ubuntu) over UDP which then does the processing that is required and sends control commands back to the Arduino, again over UDP. The processing currently amounts to checking the internal light sensors and switching on the lights if necessary. Ultimately I want to migrate all my lighting to 12v LED so I can run off stored solar, but at present I am using a system similar to yours in that the relays are in series with the power switch for the lights, normally closed, so that if the control circuitry fails the light switches should operate as normal.
I also have some external IR sensors and the same system activates an external security light, this time with a normally open relay.
I consider using the normally closed relays as essential for the main lights, otherwise the domestic management will kick off once the system is rolled out to the rest of the house.
I want to use LEDS because of their dimmable nature when using the PWM enabled pins of the Arduino, this will then enable a nice low level of light for those nocturnal toilet trips, all automatically of course.
I have just taken delivery of a Mega 2560 which will provide a lot more IO. Like yourself I envisage having separate Arduino's for input and output.
I am developing the control system in python, with the intention of migrating it to raspberry PI once development has finished. This will allow me to run it all an enclosure with a status screen hooked up to the composite video. I currently have a limited status screen running on the PC, which allows me to control the brightness of LED panels and GU16 bulbs.
I have configured the arduino so it will accept commands from any device on the network, so I can set up some control from the android devices I have around the house.
I also have a fully working zoneminder installation, but had not considered using it to trigger anything as yet, but then again I don't have any internal cameras on that, just external.
I did consider thermal imaging, as you suggested, but I think cost is a major issues (would need to come in at below $100 Australian, per room to be feasible for me), so I'm persevering with low cost IR sensors (about $2 each from China).
My Arduino code is not best but I am more than willing to share it.
It is currently set up to monitor the various sensors in a constant loop, and also listens for a 3byte UDP string in the form of 410 (4 is light 4, 1 is for on, the last digit is used for a brightness level for the LED)
I do agree with the comment about the resale values of the house, but I'm not planning to move anytime in the foreseeable future. Your needs may be different.
The python code also does some DPMS control of the monitors in the workshop. Currently they are put to standby after 10 minutes of no workshop movement.
I am in the process of setting up some power sockets that are switched in the same way as the lights, so the system can turn off things like my soldering iron and amplifiers that I frequently forget to leave on.
Let my know if I can be of any help with your project. It sounds great. Good luck
John
I did exactly that some years ago, replacing the light switch with an X10 remotely controllable switch, and hang the remote on the wall at the other end of the room. However, that approach will NOT work with LED bulbs, due to the way it powers itself, and may not work safely with fluorescents. (X10 is the low-budget brand which introduced carrier-current control signalling; there are better versions of the same system and alternative systems but they cost twice as much and require more planning in the house wiring.)
Remote-controllable devices do exist that screw in between the bulb and its socket. However, those obviously add significant bulk, and may not fit in the fixture (or may look pretty darned ugly).
A better solution may to be leave the room fixture alone and set up remote control of a floor- or counter- mounted lamp. That would provide sufficient light for you to navigate the room until you can get to the far end and turn on the overhead lights.
Best Answer
Steam technology:
You'll need to pull a bunch of cables through walls. Some of these will be 4-core. I can say with great confidence it's illegal to do this without landlord permission.
Smart-switch technology:
This is simplicity itself. They make smart switches which work with wireless remote switches that run on batteries, have no wires, and simply stick to the wall. You need to reconnoiter which wires are present in the old switch box to aid in product selection.
The key to finding masters and remotes that work with each other is they will almost certainly be the same brand.
Further, you should be aware that anything from the following channels is all but guaranteed to be the unsafe, illegal junkstream of poorly made goods from Alibaba: a) AliExpress, b) eBay, c) DealExpress, d) Banggood, and e) Amazon Marketplace (pretty much anything on Amazon, sadly). So you can save a lot of time/confusion by avoiding these channels altogether.
Honestly your best bet is your local home improvement retailer's web site (e.g. Wickes or Menards), or actually walk in to your local lighting supply house or electrical supply. They will seem very expensive because they sell a higher quality product that is properly safety certified, and they charge a higher markup than mail order, but they don't charge shipping. It is worth paying them for their knowledge if your time is valuable. Having a good relationship with an electrical supply house is invaluable when doing projects, because they will save you a fortune by steering you away from expensive mistakes.