Communication technology you'd use for new deployment



  • Hi all,

    As I see from the posts, most people go for wireless solution.
    I can understand the reason, no need to change the cabling too much... BUT I don't want to use wireless for many reasons.
    Assuming I have the cabling infrastructure prepared for smart home installation... What technilogy would you use for wired deplyoment?

    For now I'm up to 2 directions:
    RS-485 and KNX
    KNX is a great technology, developed specifically for smart homes, uses only 2 wires for power AND for communications, allows star and tree connections of the nodes, so that's basically a heaven option. The bad part is that the components are not that availalbe on the market in my area, and their price is very high. Another bad point for that option is that the device needs a large capacitor to store some energy for communication while the same lines will not be stable during the transmissions, meaning DIY devices will be pretty large.

    RS-485 is a cheap and easy to get option. It requires separate power lines and 2 lines for communication. Since I have separate infrastructure for that, I think that will not be a prbolem. Another benefit for RS485 is a possibility to get much higer speeds (probably 100's of KBits compared to 9600 for KNX). The bad part for 485 is that the devices should be connected in a line, junctions should have active repeaters. Since most of the trunks that I would connect in a star or tree topology are getting to a central place in the house, I could probably mux all those lines on the master device, that means a bit more complex master hardware, but since the trunks will be shorter, I could get higher transfer speeds from all the connected devices.
    For now I'm more inclined toward the RS-485, but still open for other options.

    Do you have any more ideas for a deployment?

    Thanks,
    Alex


  • Mod

    Rs485 is good if you do cabling correctly. I prefer cables too if it's possible (like security sensors) but I don't dislike wireless for other uses. I don't know how much data you will be transferring from your devices that you need those high speed, but for normal home automation slow speeds should be enough.



  • My plan is to use rs-485, but my experience is all still theoretical so confirm anything I say here.

    Higher speed and longer distance require better wiring, but a house should be well inside the limit even, if you snake a single wire all the way around the house. According to this link you may even be able to get away with some star topology
    https://arduino-info.wikispaces.com/RS485Info

    It seems the biggest issues on this forum with rs485 are collisions, and correct use of terminating and pull up/down resistors on the line. There is a lot of information and solutions to these out on the net. A separate ground wire is often one of the recomendations, but the inexpensive modules i have only have A and B, so im not sure exactly how the ground is wired in.

    My thinking is I will divide my house into zones, with a separate rs-485 net for each, reducing length, number of devices(collisions), and possibly less grounding issues.

    Ive heard the max485 chip isnt the best, so possibly buying better modules would be helpful. Maybe rs-422 or CAN might be other options.



  • @gohan said in Communication technology you'd use for new deployment:

    Rs485 is good if you do cabling correctly. I prefer cables too if it's possible (like security sensors) but I don't dislike wireless for other uses. I don't know how much data you will be transferring from your devices that you need those high speed, but for normal home automation slow speeds should be enough.

    I agree, slow speeds are enough for the automation. KNX is only 9600bps.
    I guess it's like the hard disk size, the more you have, the more you'll use.
    My plans include image/video capturing from entry door camera to show it on the intercom LCD and record it in the controller so I could check later who came to visit when I wasn't at home.

    I belive I'll have to use wireless in places where I didn't think I'll need the cabling, so I don't rule it out completely.

    Thanks,
    Alex


  • Mod

    For image capture, I think IP cameras are a proven reliable technology so far.



  • @wallyllama said in Communication technology you'd use for new deployment:

    My plan is to use rs-485, but my experience is all still theoretical so confirm anything I say here.

    Higher speed and longer distance require better wiring, but a house should be well inside the limit even, if you snake a single wire all the way around the house. According to this link you may even be able to get away with some star topology
    https://arduino-info.wikispaces.com/RS485Info

    It seems the biggest issues on this forum with rs485 are collisions, and correct use of terminating and pull up/down resistors on the line. There is a lot of information and solutions to these out on the net. A separate ground wire is often one of the recomendations, but the inexpensive modules i have only have A and B, so im not sure exactly how the ground is wired in.

    My thinking is I will divide my house into zones, with a separate rs-485 net for each, reducing length, number of devices(collisions), and possibly less grounding issues.

    Ive heard the max485 chip isnt the best, so possibly buying better modules would be helpful. Maybe rs-422 or CAN might be other options.

    This website talk about tens of meters wires to allow star configuration, I don't think it will be enough for any home
    installation.
    I found a discussion with a TI engineer about star topology and he strongly rejected the idea and explained it from the aspect of too many terminator resistors will lower too much the resistance between the lines (resistors in parallel), so there will be much higher current draw from the drivers, which will eventually fail from too much load.

    I plan to run a 2-core wire for power and 2 twisted pais for data (telephone cable, only one pair will be used for RS485). Thinking to use the additional wires as interrupts indicators, so all the devices and the gateway on the same trunk will know if there is something to say on the other end.
    Since RS485 are half-duplex, the gateway will have to ask every node what does it have to say, that way there should not be any collisions. The interrupt lines could save the questioning round if all the nodes are sleeping and there is nothing to transmit.

    For now, if I go with RS485, I'd like to try multiplexing the trunks using 2 analog MUXes (one for every data line), so the gateway could address every trunk separately. The interrupt lines could help to decide what trunks to check every time.
    If MUX won't work, adding few more RS485 chips are also possible, those are pretty cheap.



  • @gohan said in Communication technology you'd use for new deployment:

    For image capture, I think IP cameras are a proven reliable technology so far.

    Agree. That's a plan B for me.
    I have a building intercome with LCD screen next to the entry door and hope to find a way to hack it, so I could display there the pictures that will be captured from the door camera.
    If it won't go, will try to use my own monitor and display there the building entry camera when someone calls my appartment from the lobby.

    Hope my building manager is not in that forum 🙂


  • Mod

    I hope too. Good luck with that.


 

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