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Intelligent buildings

Discussion in 'Misc Electronics' started by Mark Carroll, Oct 11, 2003.

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  1. Mark Carroll

    Mark Carroll Guest

    I'm interested in toying with intelligent building stuff to take a a
    case study for a demo, and real hardware tends to impress more than

    The sort of scenario I have in mind is having centralized computer
    control in the loop between switches and lights, monitoring door
    contacts and activity-noticing passive infra red sensors, between
    climate controls, thermometers, and heaters, etc. so that we can play
    with simple things like monitoring patterns of lighting usage, then
    replaying them to make the building look still-occupied, and more
    complex things like trying to tell when someone's left the heating way
    up and the door open but has probably left the area.

    Here are my guesses about a cheap, adequate solution.

    For a small enough building, one could have a single computer talking
    to all these things on a common low-speed serial bus. There seem to be
    stock chips around that can talk a range of serial protocols, and a
    bus with unremarkable wiring and haphazard topology would probably
    work well enough. The computer could be preset with what is on the bus
    where. There would be single-bit things like switches that the
    computer polls frequently to check their state. There would be
    single-bit things like lights that it writes to (the written value is
    held by a latch, and the control signal/circuitry is isolated from
    what may someday be a real 110V AC circuit by a suitable relay). There
    might be things like thermometers and dimmer switch arrangements that
    convey more than a bit of information.

    Each entity on the bus could be addressed by the computer via a unique
    device ID, that matches DIP switch settings on the little circuit
    board of the entity, an ID with enough bits that random/corrupted data
    is unlikely to match.

    It seems that a couple of wires would be needed to carry 0V, +5V,
    another couple of wires might be needed for sync and data lines for
    selecting particular devices by ID (wires which might double for both
    "selecting" the device, and telling it how long to keep its state
    wired to the bus once selected), and maybe a separate wire to carry
    that state, whether single-bit or analog signal, input or output. It
    seems unnecessary to carry multi-bit digital data around as the read
    or written state of the entity, given that the devices I can think of
    that have more than binary state don't need that state to be perfectly
    accurately reported - there can just be one A/D and one D/A converter
    at the computer end that gets it approximately correct.

    So, how crazy does that sound? Would others do it differently? How few
    wires can I use while keeping everything fairly easy to design in a
    compact, cheap way? Before I start working out specifics, I figured
    it's probably good to make sure that the overall concept isn't already
    seriously flawed.

    -- Mark
  2. Mark Carroll

    Mark Carroll Guest


    I should add that "serial protocol" sounds a bit grand given that a
    shift register would probably do. An entity could probably be selected
    while the upper bits match its ID and the lower bits match a standard
    pattern that is not a subsequence in any ID.

    The main thing I don't get is how to store analog state without drift,
    for an entity representing a dimmable light or something. It'd be nice
    if there were a simple elegant solution, or something prepackaged on an
    IC, instead of me having to use an A/D converter, a few flip flops, and
    a D/A converter.

    -- Mark
  3. Gary Tait

    Gary Tait Guest

    Whereas On 11 Oct 2003 14:00:29 +0100 (BST), Mark Carroll
    Use micros, each custom programmed with it's operating code, with its
    address coded into the code, or an on board EEPROM.

    You'd trigger a triac as needed, no need to do anything directly
  4. Mark, sad to say, but I really don't believe that there is any really
    practical method available for accomplishing this. That analog systems
    have drift is a fact of life that has to be dealt with. This is one of
    the primary reasons for the popularity of digital controls when they
    first became available. It is also the reason that analog computer hit
    a peak of popularity back in the 1950s and 1960s, but are rarely found

    If you go back into history, motor driven potentiometers and chopper
    stabilized operational amplifier were arguably an approach to
    achieving stability, but couldn't compare to the stability performance
    provided by digital techniques.

    Harry C.
  5. Mark Carroll

    Mark Carroll Guest

    Surely the choice of trigger point on the AC cycle would be a settable
    "variable" too, though, whose state would have to be maintained
    between writes, so the problem of storing the state has just been
    pushed further back?

    -- Mark
  6. The appropriate newsgroup for this is sci.engr.heat-vent-ac


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  7. Mark Carroll

    Mark Carroll Guest


    No, it isn't. Not only did my question include mention of lighting,
    passive infra red sensors, etc. as having equal billing with climate
    control, but if you bother to read it then you'll see my question is
    really about how to have very simple devices on a bus where a computer
    can read state from some and write state to the others. That is very
    much an electronics question. The only relevance of the intelligent
    building stuff is that it means that the aforementioned state is a
    single binary or a single analog value, so my question would be rather
    off-topic on sci.engr.heat-vent-ac given that it's more about clocked
    shift registers, flip flops, data buses, etc. Make it about, say,
    controlling sets of traffic lights and monitoring traffic sensors and
    light levels (to guess weather and time of day), with nothing to do
    with climate control, and the answers to my question are unchanged.

    -- Mark
  8. Gary Tait

    Gary Tait Guest

    Whereas On 11 Oct 2003 23:36:28 +0100 (BST), Mark Carroll
    It will be stored in a digital register of the chip (presumeable a
    microcontroller), that triggers the triac.
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