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Thread: A Power Conscience System - (normally off system)

  1. #1
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    Default A Power Conscience System - (normally off system)

    I'm looking to automate my home and want something that will not consume any energy when not in use. From what I gather from the X10 and similar systems are that each wall unit will need to be in standby mode 24/7 in order to receive signals. The energy consumption from each module is probably not enormous, but adds up. In fact, if you consider all the systems (TVs, VCRS, battery chargers, etc) in every household around the world that are in standby mode, when they could be off, it adds up to a lot of wasted power consumption.

    I will be rewiring my home soon, and plan to add a serial port or other interface to each room in the house. So automation over the power lines is not required. I'm hoping a solution already exists. If not, I have an idea for how it will work:

    Each room unit would have a 4-pin interface to the central computer: 1) Power, 2) Ground, 3) Data, 4) Wakup. The central computer would supply the power and all units would be off by default. Whenever the central computer sends a command to a new unit it would send enough power in the wakeup line to power up all units momentarily. Each unit would check if the command was for it (by a unique serial number) and either execute the command and stay online to interface with the system or turn off until woken again.

    This type system would be perfect for a energy conserving home. You could have the system power down your TV and other standby systems, without the unit needing to stay online to receive commands.

    Is there already a system and/or interface that does this? Can somebody recommend implementation ideas? What sort of data interface should I use to communicate with each unit over a single wire (RS485)? Can I send power over the data line to cut the interface down to a 3-pin system? Iím just a novice electronics hobbyist and can use all the advice you have. Iím a software engineer by trade and know basic electronics (learning more all the time) and how to use microcontrollers.

    Thanks,
    Jeremy

  2. #2
    Automated Home Legend Karam's Avatar
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    Jeremy,

    Its probably depends on what level of automation you want to achieve. Also I think there is some heightened awareness of the subject of standby power. Much has been criticised about AV standby power with all sorts of gizmos to switch off the AV kit completely etc. Whereas really what should be happening is manufacturers redesign their standby circuits to be very power frugal, which BTW should be easily possible.

    To put things into context many automation modules these days consume very little power when idling, for example most of our own modules only consume about 70-90mW if they are not driving some sort of output device, so even if you had 100 of them that's only 7-9W. You could reduce this even further by making the modules go completely idle until they see any network activity and/or have a duty cycle arrangement where a module wakes itself up every so often (a method used by RF modules to achieve massive reductions in power consumption) but sometimes this compromises reaction speeds where important eg. occupancy detectors for lighting.

    What typically takes more of the power however is any sophisticated controller eg. PC based or even embedded - again depends on how much automation you are after, possibly several 10s or few 100s of Watts. Also any actuation/output devices such as relays, displays, audio, indicators and so on.

    So in a nutshell you can already get pretty miserly power consumption with existing technology if the automation application is limited to relatively modest remote/scheduled control type operations (which in our system can be done with no other controller than the modules themselves - see Reflex). The operation of any output devices can be looked at on a case by case basis to maintain efficiency, for example bistable relays could be used for power control (these only require energy to switch over from one state to another).

    Having said all this it might not be a bad learning exercise to experiment with your own ideas if you're that way inclined - and who knows maybe even come up with a great solution.

    If you want to use the concept of a wakeup signal you may not need a separate line ie. presence of or leader in the data signal can itself be used as a wakeup trigger quite easily for most microcontroller setups which then themselves might wakeup secondary power devices on the particular module board. A microcontroller can typically be set up in such a way as to consume only microamps whilst its awaiting a wakeup trigger. Also running the micro at low clock speeds and low voltages will significantly reduce its power consumption when not asleep. Superimposing data on the power lines is also possible by various methods with possibly a small amount of overhead in electronics depending on the communication methedology. RS485 might be good enough for a slave/master type arrangement and probably a good starting bet for control signal communication. Now all you need to think about is a protocol and what you actually want to do with the system :-)

    Karam
    IDRATEK LTD

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    Thanks for all the information -- it really does put everything into perspective. The system I want will be more than just turning applications on and off. I'd like to be able to control security cameras that send their pictures back to the server. Voice recognition is a long-term goal. And potentially any thing else. Right now I'm just gathering ideas and information.

    - Jeremy

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    Moderator toscal's Avatar
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    At the moment I can turn the power off to my TV using an X10 appliance module. I use a Harmony remote control so at night time I just press the bedtime button on the remote and this turns off the power to the TV and gradually turns off the lights in the house. The IR from the remote is picked up by my Homevision controller. Once I get my house PC up and running again I will program the Homevision, so that when I turn on the appliance module for the TV the Homevision will after a 2 second delay issue an IR command to turn the TV on. The 2 second delay is for the TV, as it takes about 2 seconds after switch on before it will reply to any IR commands. Don't know if this will save much on our electricity bill but I guess its a start.
    For details on the Homevision Controller have a look here www.csi3.com

  5. #5
    Automated Home Legend Karam's Avatar
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    I think X10 appliance modules use bistable relays which is good since should not use up more power when the socket is ON as compared to OFF, but the module electronics probably draw 3-4 watts (based on a vague memory of ~20mA current and excluding any power factor considerations). One consideration when switching power off completely to some AV equipment is that some tend to lose certain settings or clock time. With some sort of HA system in control it may be possible to re-program these back automatically after switch on.
    From experiences to date more significant energy efficiency gains are likely be found in better controlled HVAC and automation of lighting. Remember also that it may be possible to take into account/utilise other inputs/outputs which might not be considered in more traditional control systems for example actuated blinds, skylights, curtains, state of doors and so on.
    Of course its probably much better to have good insulation, heat recovery ventilators and more efficient lighting technologies. Also the gains are likely to be climate dependent :-)

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