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Two wires bus for data and power

Started by pozz April 18, 2016
There are many commercial solutions for home-automation systems that are 
based on a two wires bus both for bidirectional data and for powering 
the modules.  The number of connected modules could be high, 100 or more.

What is the technology of those kind of buses? Are they simple 
half-duplex RS485? In this case, how the power can be distributed on the 
same wires of data? Is the protocol master/slave? In this case, the time 
to poll all the modules could be some seconds and the reaction of user 
commands is very bad.

Or are there other solutions?
luni, 18 aprilie 2016, 13:12:49 UTC+3, pozz a scris:
> There are many commercial solutions for home-automation systems that are > based on a two wires bus both for bidirectional data and for powering > the modules. The number of connected modules could be high, 100 or more. > > What is the technology of those kind of buses? Are they simple > half-duplex RS485? In this case, how the power can be distributed on the > same wires of data? Is the protocol master/slave? In this case, the time > to poll all the modules could be some seconds and the reaction of user > commands is very bad. > > Or are there other solutions?
24VDC is the minimum I'm aware of. There are also solutions for 220VAC. You need quite expensive specialized driver chips. These are like RF chips: they modulate some frequencies on the carier wire like the RF parts do over the air. For details search the web, but this is the basic technology.
On 2016-04-18, pozz <pozzugno@gmail.com> wrote:

> There are many commercial solutions for home-automation systems that are > based on a two wires bus both for bidirectional data and for powering > the modules.
There are a few. HART, Foundation Fieldbus H1, Profibus MBP, etc.
> What is the technology of those kind of buses? Are they simple > half-duplex RS485?
No. Typically you AC-couple manchester-encoded (or FSK) data onto the wire-pair. You also have to add a filter to your power-supply to make it high-impedance at the comm frequencies. -- Grant Edwards grant.b.edwards Yow! Now that I have my at "APPLE", I comprehend COST gmail.com ACCOUNTING!!
>Or are there other solutions?
I did a two part blog on some of the options http://www.embedded.com/electronics-blogs/without-a-paddle/4439353/Combining-power-and-data-wires--Part-1 http://www.embedded.com/electronics-blogs/without-a-paddle/4439429/Combining-power-and-data-wires--Part-2 I hope this helps a bit -Aubrey --------------------------------------- Posted through http://www.EmbeddedRelated.com
On Mon, 18 Apr 2016 12:12:45 +0200, pozz wrote:

> There are many commercial solutions for home-automation systems that are > based on a two wires bus both for bidirectional data and for powering > the modules. The number of connected modules could be high, 100 or > more. > > What is the technology of those kind of buses? Are they simple > half-duplex RS485? In this case, how the power can be distributed on the > same wires of data? Is the protocol master/slave? In this case, the time > to poll all the modules could be some seconds and the reaction of user > commands is very bad. > > Or are there other solutions?
The general idea is that you use diplexers everywhere, to separately couple DC and comms onto the same set of wires. But -- there's a reason that wireless is popular. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com
Grant Edwards wrote:
> On 2016-04-18, pozz <pozzugno@gmail.com> wrote: > >> There are many commercial solutions for home-automation systems that are >> based on a two wires bus both for bidirectional data and for powering >> the modules. > > There are a few. HART, Foundation Fieldbus H1, Profibus MBP, etc. > >> What is the technology of those kind of buses? Are they simple >> half-duplex RS485? > > No. Typically you AC-couple manchester-encoded (or FSK) data onto the > wire-pair. You also have to add a filter to your power-supply to make > it high-impedance at the comm frequencies.
A proprietary system that I once worked with used a DC voltage for logic high and a somewhat lower DC voltage for logic low. Peter
Il 18/04/2016 14:49, raimond.dragomir@gmail.com ha scritto:
> luni, 18 aprilie 2016, 13:12:49 UTC+3, pozz a scris: >> There are many commercial solutions for home-automation systems that are >> based on a two wires bus both for bidirectional data and for powering >> the modules. The number of connected modules could be high, 100 or more. >> >> What is the technology of those kind of buses? Are they simple >> half-duplex RS485? In this case, how the power can be distributed on the >> same wires of data? Is the protocol master/slave? In this case, the time >> to poll all the modules could be some seconds and the reaction of user >> commands is very bad. >> >> Or are there other solutions? > > 24VDC is the minimum I'm aware of. There are also solutions for 220VAC. > You need quite expensive specialized driver chips.
Quite expensive? They are products for consumers. It isn't a low-end market, but it isn't industrial too. It's very simple to have 50-100 modules on the bus even for small-medium private buildings (homes).
> These are like > RF chips: they modulate some frequencies on the carier wire like the > RF parts do over the air. For details search the web, but this is the > basic technology.
I couldn't find any ready-to-use chips, except KNX standards that are very closed and it seems impossible to understand the technical details of the bus.
Il 18/04/2016 16:28, Grant Edwards ha scritto:
> On 2016-04-18, pozz <pozzugno@gmail.com> wrote: > >> There are many commercial solutions for home-automation systems that are >> based on a two wires bus both for bidirectional data and for powering >> the modules. > > There are a few. HART, Foundation Fieldbus H1, Profibus MBP, etc.
They seem all industrial solutions where the cost is higher than consumer market. HART seems a master/slave protocol, it can't be used for building automation applications, where you need a fast response to a push button press.
>> What is the technology of those kind of buses? Are they simple >> half-duplex RS485? > > No. Typically you AC-couple manchester-encoded (or FSK) data onto the > wire-pair. You also have to add a filter to your power-supply to make > it high-impedance at the comm frequencies.
Are there any ready-to-use cheap solutions? I don't think building automation products are based on complex and big electronic boards.
Il 19/04/2016 01:51, Pete ha scritto:
> Grant Edwards wrote: >> On 2016-04-18, pozz <pozzugno@gmail.com> wrote: >> >>> There are many commercial solutions for home-automation systems that are >>> based on a two wires bus both for bidirectional data and for powering >>> the modules. >> >> There are a few. HART, Foundation Fieldbus H1, Profibus MBP, etc. >> >>> What is the technology of those kind of buses? Are they simple >>> half-duplex RS485? >> >> No. Typically you AC-couple manchester-encoded (or FSK) data onto the >> wire-pair. You also have to add a filter to your power-supply to make >> it high-impedance at the comm frequencies. > > A proprietary system that I once worked with used a DC voltage for logic > high and a somewhat lower DC voltage for logic low.
In this case, each module on the bus should be capable to inject a DC voltage on the bus (and changes its value when transmitting). I don't think it is a simple solution. Do you remember the bitrate?
Il 18/04/2016 18:55, Tim Wescott ha scritto:
> On Mon, 18 Apr 2016 12:12:45 +0200, pozz wrote: > >> There are many commercial solutions for home-automation systems that are >> based on a two wires bus both for bidirectional data and for powering >> the modules. The number of connected modules could be high, 100 or >> more. >> >> What is the technology of those kind of buses? Are they simple >> half-duplex RS485? In this case, how the power can be distributed on the >> same wires of data? Is the protocol master/slave? In this case, the time >> to poll all the modules could be some seconds and the reaction of user >> commands is very bad. >> >> Or are there other solutions? > > The general idea is that you use diplexers everywhere, to separately > couple DC and comms onto the same set of wires.
Any ready-to-use chips or reference designs to suggest?
> But -- there's a reason that wireless is popular.

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