Sounds cool. That’s something I’ll be doing once I get to the home-owning stage.
What protocol are you using? RS485 (if so, what on top)? X10?
ELV ( ie 5 or 12v or similar DC, 50mA current is what matters here) used to
switch a 240V AC rated mains via an appropriate SSR at each
light-switch.
What sort of cable are you running it over?
Cat6… is there any other sort? This allows me to change the setup in the
future to use RS485, or Ethernet, or some other protocol if I want
to.
How are you powering the control circuitry? Dropping down the mains at each point, or running something lower and DC along with your comms cable?
The “control circuitry” ( ie the intelligent part/s ) is
centrally located in a “server room” ( closet). From there, the on/off
logic runs as DC to each SSR, which is located at each light-switch.
What’s the reason for wired over wireless? (I would do it because it’s: more secure, less prone to interference, and can run DC along with it - but am keen to hear your reasons)
Absolutely to do with reliability, speed, cost, etc.
cost:
wifi or any other “wireless” module at each lightswitch means having to have
a cpu located there ( $2-$10), and an appropriate wifi, bluetooth, or
2.4g type adaptor ( $5-$20) , and a way to power each of them , such as
a buck converter, or transformer/rectifier, or similar ( $2-$10), or a
DC power cable to each location.
reliability / speed, etc.
20-50 cheap $2 wireless modules all splashing around on the same frequency sounds hard
to write code for, especially if you want your light-switch actions to
“feel” instantaneousm and work 100% of the time.
20-50 more complicated wifi modules, will also cost $10-$15 each, and even they will suffer
from interference and latency etc.
DC over cable is 100% reliable ( except for wiring issues, and RF interference, which can be dealt with easily enough ).
If this doesn’t work as-is, eg, I get interference, I could, for example:
1: change it to use an attiny at each location ( under $1), and a rs485
tranciever chip( DS75176B or similar, $1 each) allowing a max cable
length over 2km…
2: Or I could just just use RS232 without any extra components ( other
than the attiny at one end, and the Arduino Mega at the other end), and
multiplexed Sftware Serial… sounds crazy, I know… but the max
length in the standard is 50ft at 19200 baud, but practically, you can
1/2 the baud rate, and double the length a few times to get over 3000ft
at 2400 baud, if needed, so long as your cable voltages are sufficient,
and not just running at 3.3 or 5v.
3: Or I could do something different that I haven’t thought of yet. 