Home automation Q's

[heydonms]

I've been planning to build some home automation gear, originally I had intended for each light switch to have its own independent module. Unfortunately the cost the power supply components is causing problems with that approach and I am now considering other options (like several "region controllers" each of which powers and controls a number of nodes).

Can anyone suggest:
1) A cost effective way (<$6) to convert ~250VAC to ~8VDC @100+mA while providing good isolation? Transformers tend to be fairly expensive and most switch mode are either expensive or won't take input that high.
2) A simple communications protocol that uses a physical star topology and can easily be implemented on a low end uC?

I've got a few other ideas, but if one of the above exists then I think I can come up with a better design.

TIA

 

[Reloadron]

The 100 mA is nothing, how critical is the 8 volt regulation? I would think about getting a Euro type wall wart 240 VAC / 9 VDC (or similar) and just place a 1N4001 diode (or two) in series with the + wall wart output. Just about any 240 VAC wall wart will work fine on 250 VAC.

Just My Guess
Ron

 

[KeepItSimpleStupid]

I can't find it by searching, but there was an advertisement for a power supply that is designed to FIT in the bottom of an electrical box.

Found it: https://www.rutronik.com/news M5966f49f629.html

and:

https://www.digikey.com/product-search/en?vendor=0&keywords=rac03

 

[NorthGuy]

I2C is probably suitable for star topology if you do transfer some information. Otherwise some sinple bit-bang will work.

You can even use remotely controlled relays in which case you do not need any protocol at all.

 

[ronsimpson]

I2C is for short distance. (a couple feet)
I have used RS232 over the distance of the house. BUT RS488 is much better.

I have good luck with X-10. It is old school. Some people have problems with it.

There are some stores:
https://www.smarthome.com

I use cell phone chargers for remote power.

 

[heydonms]

The 100 mA is nothing, how critical is the 8 volt regulation?

Not at all, 8V is just a target, but anything up to 30ish V would be OK, it is just going to be fed into a linear Vreg.

I would think about getting a Euro type wall wart 240 VAC / 9 VDC (or similar) and just place a 1N4001 diode (or two) in series with the + wall wart output. Just about any 240 VAC wall wart will work fine on 250 VAC.

The devices will be hard wired not plug-in so I would need to pull the board out of the wall wart and integrate it into the device. While I'm sure it would work, it seems messy and unpleasant to work with. Also wall warts from a local electronics shop are ~$10, I could get a $1 phone charger off ebay but I doubt it would have the level of isolation, reliability and safety that I am looking for. I could get one of the cheap ones and try to make an improved clone but I suspect that they are saving a bit due to economies of scale and after any improvements are made I am probably back up around $10/unit.

I can't find it by searching, but there was an advertisement for a power supply that is designed to FIT in the bottom of an electrical box.

That is quite cool, and I have a one or two other projects where I might look at using one, but for this project $14/unit is just too much.

I2C is probably suitable for star topology if you do transfer some information. Otherwise some sinple bit-bang will work.

I've never done wired comms over more than about 30cm, how much do I need to worry about reflections and noise? I can keep the speed down (a few Kbps would be fine) but it will be surrounded by AC wiring. I did consider using RS232 transceivers to help protect against noise, or is that overkill for a 5-10m run?

You can even use remotely controlled relays in which case you do not need any protocol at all.

That was one of my backup plans, have the region controller drive 12V lines that trigger triacs at each node. The downsides to that approach are that some advanced functions (e.g. power usage monitoring) are harder to implement, and a failure of the region controller uC will take out all of the lights in that region. If each light has its own uC then it is only dependent on the region controller continuing to provide power and in the event that no traffic is received from the controller for X seconds, it reverts to a dumb mode where it monitors the switch and triggers the output locally.

 

[NorthGuy]

I've never done wired comms over more than about 30cm, how much do I need to worry about reflections and noise? I can keep the speed down (a few Kbps would be fine) but it will be surrounded by AC wiring. I did consider using RS232 transceivers to help protect against noise, or is that overkill for a 5-10m run?

I think 5-10m is too long for I2C. RS-485 is similar to RS-232, but will let you have multi-node network.

 

[heydonms]

RS485 and CAN are both on my list of possible tools as well

I had hoped for a star topology as it simplifies wiring. I am planning to use Cat5 for the cabling so I suppose I could use one of the pairs to return the signal to the controller so I could use a physical star even through it is a logical linear bus.

 

[NorthGuy]

With slow data rates you can use a star layout. Shouldn't be a problem if your connections are not long. You can use a 4-wire telephone cable - 2 wires for power, 2 wires for signal.

CAN is a good idea, but probably more expensive.

 

[4pyros]

Why are you trying to reinvent the wheel when there are so many Home Automation systems already out there?

 

[heydonms]

Probably for the same sort of reasons you don't go buy a FireOne

Nothing has the features I want at a price anywhere near what I am willing to pay, and while I am sure some would argue that the time I spend building it would easily pay for the difference I would say that time spent learning and doing something I enjoy isn't really a cost.

 

[ronsimpson]

What computer are you using?

I have many modules on cat-5 wiring. I have run RS232, 485, power and/or video over cat-5.

 

[KeepItSimpleStupid]

Where I am, wires in the same space have to have to be rated for the highest voltage present.

 

[ronsimpson]

Where I am, wires in the same space have to have to be rated for the highest voltage present.

YES, Good idea but there is a way around that.
I just finished a large breaker box in the green house. (had it inspected by the electoral inspector)
There is a row of solid state relays what switch power. The coils are driven by low voltage.
The code states 'there must be a mechanical method to keep high and low voltage wires from touching each other'.
I brought the control wires in from the side/back and to the relays. Then I added a metal plate (could have used plexiglass) to separate the control wires from the power wires.

I have used tubing that caries the control wires to the relays. Any thing that will keep the wires apart will work.

 

[KeepItSimpleStupid]

Yep.

 

[4pyros]

Probably for the same sort of reasons you don't go buy a FireOne

We have many FireOne's, don't get it?

 

[4pyros]

Nothing has the features I want at a price anywhere near what I am willing to pay, and while I am sure some would argue that the time I spend building it would easily pay for the difference I would say that time spent learning and doing something I enjoy isn't really a cost.

Fair enough.

 

[heydonms]

What computer are you using?

Probably PICs for the most part. The master controller will probably be a 32bit and the rest will probably be 8bit. I'm not getting too bogged down in details like uC selection since I know that there exists some product that does what I need it doesn't really matter whether it is PIC, AVR, etc.

Where I am, wires in the same space have to have to be rated for the highest voltage present.

Yep, I've spoken to a local sparky who will assist me with the final install. There are requirements for isolation ratings, minimum separation and/or conduit. I'll try to keep them as far apart as possible and where the bus has to run near AC it will go in conduit. The boards will be designed to keep the LV and ELV separated. Prototyping will be done very carefully

We have many FireOne's, don't get it?

I saw you asking about pyro gear and assumed you were an amateur, most amateurs aren't willing to spend the money to get a professional firing system.

 

[4pyros]

I saw you asking about pyro gear and assumed you were an amateur, most amateurs aren't willing to spend the money to get a professional firing system.

No amateur here. We just need more to use once a year.

 

[ronsimpson]

What computer

Probably PICs for the most part. The master controller will probably be a 32bit and the rest will probably be 8bit. I'm not getting too bogged down in details like uC selection since I know that there exists some product that does what I need it doesn't really matter whether it is PIC, AVR, etc.

For the master computer I am using a basic tiger. I am working to replace it with a beagle bone black. The idea is to get onto the internet in a better way. I wan to see the house on my phone from anywhere. (even the living room) There is some real advantage to have the house computer on the wifi.