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Power Software

Saving Energy Via Webcam-Based Meter Reading? 215

squoozer writes "Like many people, I am trying to cut down on the amount of energy my family and I use in order to save both the environment and my pay packet. Since I want to do this in as scientific a way as possible, I'm taking meter readings every day and recording them in a spreadsheet (OOo Calc naturally). Currently, in the UK at least, neither gas nor electricity meters can be hooked up to any sort of device that can query the meter for its current reading. Rather than climb down into the cellar every day to read the meters, it would be great if I could simply position a webcam in front of each meter and have the value logged automatically each day. The problem is that while I am a software developer (Java mostly) I have no experience in image processing (dials from the electricity meter) and don't really know where to start with this project." Does anyone have any advice for analyzing the visual data this reader would be gathering?
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Saving Energy Via Webcam-Based Meter Reading?

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  • But you must not block the meter dials from view. Someone goes to check the values manually, every once in a while (monthly?).

    If you have the same kind of "spinning wheel with a mark" under the small dials, it might be easier to check for the number of revolutions of that wheel.

    • A note, I'm in Canada too, and maybe it's just the neighborhood I grew up in, but all the meters were on the outside of the house. I'm not sure how effective hooking a web-cam rig to the side of your house would be.

      Also, since the OP says the meter is in the basement, I'm assuming low light. This means you'll need to light the meter every time you want to snap a photo of it-- or leave a light on all the time. I have to wonder what that would do to your hydro bill...?

      • It's easy enough to get webcam with efficient infrared LEDs that light up a small area.

      • Re: (Score:3, Interesting)

        by rew ( 6140 )

        FYI, here in holland you just pay a guesstimate every month, and they give you a final bill every year.

        They try to get a meter reading every year. They trust you to do it yourself. They send a guy over every once in a while (i.e. every 5 years or so) to keep you honest. All you can do is postpone the stuff for a while. If you move you either have to arrange for an official meter-taking, or you have to sign a common "agreed meter-positions" note with the next inhabitant.

        Apparently they HAVE to check the read

        • Note that in Holland they -are- rolling out the new 'smart meters' which basically phone home periodically on how much your usage has been.

          This is seen as 'good' for everybody all around.. you no longer have to mail/phone in the numbers once a year (gee, a 3 minute job), and you get a nice view online (or by mail - frequency depends on the utilities company) of what your use has been. So you never have to pay more than you should have to (because the utility company's 'assumption' falls too high - say, if

    • by the_other_one ( 178565 ) on Wednesday November 12, 2008 @05:48PM (#25739183) Homepage

      But you must not block the meter dials from view. Someone goes to check the values manually, every once in a while (monthly?).

      If you have the same kind of "spinning wheel with a mark" under the small dials, it might be easier to check for the number of revolutions of that wheel.

      Of course your biggest power drain will be from the computer that is always on reading the meter.

      • Of course your biggest power drain will be from the computer that is always on reading the meter.

        I can see it now, a 1kw rig with 4 geforce cards, 32 monitor, 800 watt stereo, lit up like the sun with ever light and fan this side of new egg... all just to read the power meter.

      • "Of course your biggest power drain will be from the computer that is always on reading the meter."

        You mean you don't normally leave all your computers on 24/7 anyway?

      • A few people have commented that the computer used to take the readings will be a large power drain but I have to run a server 24/7 for my business anyway so the software will simply run on that. It would also be possible to run a tiny little ITX based box that draw hardly any power. From experience anything less than about 90W and my antiquated meter to turn.

      • by AmiMoJo ( 196126 )

        Of course your biggest power drain will be from the computer that is always on reading the meter.

        That's why the only sane way to do this is with a microcontroller, like an AVR. Log to an SD card or maybe even ethernet. Add an LCD for realtime display. Power usage can be under 1W.

        The way to read the meter is not to try and do image processing, but to try and sense the notch on the spinning dial. Just shine an IR light on the dial and use an IR detector to sense when the black mark passes by.

      • Of course your biggest power drain will be from the computer that is always on reading the meter.

        Yes, if you choose to use a constant-monitor system to count ticks (like phk does). But, if you can actually read off a dial, like the OP says he can, one can get by with using a periodic snapshot ... and image processing.

    • Re: (Score:3, Interesting)

      by jkerman ( 74317 )

      They changed all our electricity meters (madison, WI) to wireless now. they just drive the truck by and read them all instantly.

      I assume it would be getting popular elsewhere too. it would be fun if you could tap into that.....

  • by Hatta ( 162192 ) on Wednesday November 12, 2008 @05:13PM (#25738767) Journal

    My meter reads in kilowatt hours, not amperes.

  • what's your goal? (Score:5, Insightful)

    by gEvil (beta) ( 945888 ) on Wednesday November 12, 2008 @05:16PM (#25738807)
    I'd say your approach completely depends on your goal. If your goal is as stated, then I'd use the webcams to get shots of the meters, then I'd take the 2-3 minutes or whatever it takes a week to pull up those images and transcribe their values into the spreadsheet. If the goal is a programming exercise, then go to town with figuring out some way to automate that few-minutes-a-week task. Of course, in order to do that, you'll expend a whole lot more energy than you'd take to read the meters (via the webcam shots) yourself.
    • Re: (Score:3, Funny)

      by greg_barton ( 5551 )

      Of course, in order to do that, you'll expend a whole lot more energy than you'd take to read the meters (via the webcam shots) yourself.

      You are hereby ordered to report to the home office and turn in your geek card.

    • by Erioll ( 229536 )

      Not to mention that if he's trying to SAVE energy, how much energy is the webcam + computer hooked up to watch this thing consuming?

      • Well, once he gets his contraption set up, he can find out!
      • Re: (Score:3, Insightful)

        by jibjibjib ( 889679 )
        He probably has a computer running all the time anyway. And a webcam presumably doesn't consume much power, especially if it's turned off most of the time and just wakes up occasionally to grab a single frame.
      • by kv9 ( 697238 )

        Not to mention that if he's trying to SAVE energy, how much energy is the webcam + computer hooked up to watch this thing consuming?

        whenever I hear of these power saving hippies I chuckle and try to throw another server in my power guzzling rack. to balance things out.

    • by raddan ( 519638 )

      "Reasonable people adapt themselves to the world. Unreasonable people attempt to adapt the world to themselves. All progress, therefore, depends on unreasonable people." —George Bernard Shaw

    • Re: (Score:3, Interesting)

      by LoRdTAW ( 99712 )

      He should just buy a digital watt hour meter that uses 2 piece or clamp type current transducer coils. It might use rs-232 or usb and just read in the values from the device. There are plenty which are commercially available.

      You can make your own using a micro controller with a few A-D channels to read the values of the current transducers and voltage using isolating transformers. Then just read in the two values, figure out the power factor and multiply the volt-amps by the power factor for watts. Then jus

    • Try the "oops I dropped my Blackberry into the toiler" upgrade. Take a hammer and beat the crap out of your meter. Call the electric company. They'll come by and replace it with one of those new ones with a serial port or one with OCRable rolling number gauges.

  • by halcyon1234 ( 834388 ) <> on Wednesday November 12, 2008 @05:16PM (#25738811) Journal

    Post the images as CAPTCHAs that protect porn pictures. You'll have the values typed in for you in no time.

    • LOL!! I'd mod you insightful if I had mod points. You really deserve some karma for that post :D

  • Depending on the color of the faceplate and the hand, you might be able to mask off everything you don't care about (say everything but a small area around the center of the dial), run it through a hi/low filter to map the faceplate to white and the hand to black, and then just calculate the angle of the hand by searching the edge of the image for black pixels. So long as the cam is fixed and you know the coordinates of the pivot point it should be trivially easy to determine the angle of the hand based on
    • by SQLGuru ( 980662 )

      The position of everything should be the same each time. Convert to black & white (not greyscale). Then, because the center positions are known and the position of each number, figure out which "wedge" the point falls into. A wedge is defined as starting with a number and proceeding to the next (like the hour hand in a clock).

      You can compute the coordinates of the wedge ahead of time. I would probably AND/OR the wedge from the picture with a known wedge to quickly compare them.

      0 indicates "filled" (

  • Rubbish (Score:4, Informative)

    by megalomaniacs4u ( 199468 ) on Wednesday November 12, 2008 @05:18PM (#25738827)

    in the UK at least, neither gas nor electricity meters can be hooked up to any sort of device that can query the meter for it's current reading.

    Rubbish. Look up smart meters gas & electric meters which update the utility company continously on usage which they can provide to you as well. (currently insanely popular after the recent documentry on smart meters)

    If your supplier is reluctant to include you in the trials, for electrical use try "Wattson" [] or other similar personal wireless power meters (also sold out everywhere, but there a cheaper more functional equivalents around)

    • Re: (Score:3, Informative)

      by camperdave ( 969942 )
      You have to clip a Wattson transmitter around a single line of the power feed from the pole into the fuse box. Most places I've seen have these wires in a conduit leading from the meter to the fuse panel. In order to clamp it appropriately, you'd need to install the transmitter inside the fuse panel itself. This is not recommended, and may be illegal in certain regions unless you're a licenced electrician.
      • The submitter is in britan. Typicaly in britan the meter is conencted to the consumer unit using double insulated single core tails which are usually exposed for at least long enough to get a clamp on them.

      • by igb ( 28052 )
        I installed such a device a couple of weeks ago, and I had several metres of cable to choose from on the link from the meter (front of the house) to the consumer unit (rear).
  • Kill-A-Watt? (Score:4, Informative)

    by corsec67 ( 627446 ) on Wednesday November 12, 2008 @05:18PM (#25738833) Homepage Journal

    A Kill-A-Watt [] might be a better choice for "power trimming", since you can get an instant reading of the power used by anything that plugs in.

    On my website [] I have a couple of webcams that I grab the image from at a specific interval and store the result. Basically, if you get a Trendnet TV-IP201 and a Pentax 10mm f/1.2 [] lens with a C-mount to CS-mount [] adapter, you can just wget the image however often you want. Image processing is another issue, but I don't know anything about that.

    • I got a hall-effect ampmeter for the purpose of measuring power usage. It works pretty well, you just clamp it around the wire you want to measure.

      The one caveat, though, which makes it far less convenient to use than it would otherwise be, is that it doesn't work if it surrounds both the positive and negative wires at the same time. I ended up modifying a power strip by cutting open the rubberized outer coating of the power cord so I could clamp the meter around just the postive cord.

      In retrospect, t

      • I got a hall-effect ampmeter for the purpose of measuring power usage.

        Alternating current times voltage only equals power if they are in phase, which is the case with resistive loads such as incandescent light bulbs and heaters.

        In equipment with transformers (halogen lighting, fluorescent tubes, electronics), and motors (refrigerator, laundry machine), the current is out of phase with the voltage, which means a correction factor ("cos phi") that can be anywhere between 0.6 and 0.9. Especially transformers

  • by randyest ( 589159 ) on Wednesday November 12, 2008 @05:20PM (#25738851) Homepage
    Your power company is probably already looking into standards like Homeplug (main org site) [] (wiki link []) that provide meter data much more accurately than a webcam and image analysis software. This allows them to save money on paying sneaker-net meter readers, and real-time usage data for load balancing and prediction.

    Whether or not they'll specifically give you access to the data is somewhat moot, since it's network-over-powerline and there are already consumer devices [] that can access the same network and (eventually if not already) be hacked to reveal the data being sent from your meter.

    It's an exploding industry (like 20-30% CAGR in the US alone, higher in other less-developed areas where the first power meters will be homeplug-capable) so I wouldn't suggest putting too much effort into your image-analysis idea at least for a few months to see what happens in homeplug-world.
  • OCR plugins? (Score:3, Informative)

    by phatvw ( 996438 ) on Wednesday November 12, 2008 @05:21PM (#25738865)
    There are many open source OCR [] tools available. Write a script to capture [] a JPG or PNG image every day from your camera and run it through one of the command-line OCR tools..

    As long as your web cam doesn't get moved, you can set static cropping on the image so only the numbers are in the jpg file without a huge complicated border than might confuse the OCR engine.
    • Re: (Score:3, Informative)

      by randyest ( 589159 )
      Cool. Which one of those can decode the five 10-position analog dials (like clock faces) that he shows in the jog in the summary?
      • by phatvw ( 996438 )
        You know what, I hope somebody mods my parent comment down. I didn't specifically say how to solve the problem. I really don't know the best way to do this, it would certainly help if the needles were a different colour than the rest of the image. Then you could just compute the angles and relative postition of the needles. Given that data, its a piece of cake.

        Going the OCR route is actually quite a bit more complicated. You'd basically have to train the OCR to recognize the dial pattern and what a "5"
        • by phatvw ( 996438 )
          Bah forget all that. Smart meters are the way to go. Problem solved.

          Of course only the true nerds look for the programming solution when there are much easier options around... but this is slashdot so I feel proud, not ashamed :)
        • Re:OCR plugins? (Score:5, Informative)

          by smellsofbikes ( 890263 ) on Wednesday November 12, 2008 @05:59PM (#25739367) Journal

          This guy [] has an algorithm run in matlab to convert dial indicator readings to numbers using MatLab. He claims 99% accuracy over 2000 readings.

        • You could also figure out which pie slice of the circle has the most black space. So split the circle into 10 36-degree segments and add up all the black pixels.

          Even simpler:
          Split the pic of each dial into the 10 segments.
          Compare today's pic segments with the stored segments.
          Whichever 1 or 2 segments checksum 'different' than the stored, that's where the pointer is.
          • Checksums don't work for comparing photos, because two photos of the same object won't be identical, due to random fluctuations in the CCD sensor and slight changes in lighting.

            (Although there are algorithms which actually will work, so your idea is good, it's just the 'checksum' part that's not quite right.)

            • Right. Not checksum, because they won't be "identical", but similar (histogram, black level, white level, whatever) within a few percent.
        • The first thing that came to my mind was OCR too; obviously I also didn't click the link :). Of course everything would've been much simpler if we were dealing with an odometer-type device here.

          The sample image should work just fine even in gray-scale. The contrast is high and the needles are pretty large, so it should be reasonably easy for anyone to just get the angle of each one and calculate the value based on that, exactly as you suggest here. One could also hardcode in the areas in which each dial is

    • I've tried using some opensource OCR programs, most notably Kooka OCR. What I was doing was (I think) the best possible situation: putting a digital multimeter with a very large readout panel face-down on a flatbed scanner and automatically scanning it and dumping the output to Kooka. It does a pretty terrible job, honestly. I'm lucky to get one digit correct half the time, out of the three digits available.
      I'm doing cropping to make sure only the digits I want are in the frame.
      If you have any suggestion

      • I assume your digital multimeter has 7-segment displays. Perhaps the OCR software wasn't designed with that sort of thing in mind at all, but works much better with printed text.
        • That's possible. I actually haven't tried Kooka or gocr with printed text, just with the multimeter's segmented LCD.

      • by yo303 ( 558777 )

        OK, if you're already doing all this, it will be pretty easy for you from here on in.

        Since you have 7 segment displays, all you need to do is mask off each segment in each digit. Check if the segment is on or off, by adding up all the pixels' brightnesses in the mask, and checking it with a threshold.

        Run through a loop comparing the state of all seven segments against the digits 0 through 9.

        Repeat for each digit.

  • "Saving Energy via Web-Cam Based Meter Reading? "

    I'd put an induction clamp onto the line in my box and get the data from that point.

    • by dschuetz ( 10924 )

      I'd put an induction clamp onto the line in my box and get the data from that point.

      Hard to do that with Gas, though.

      Plus, you'd have to measure the main (not impossible, but it might be harder to find a clamp-on inductive ammeter that's easy to interface with a computer), and you'd have to monitor it *continuously* in order to integrate over time. Whereas the webcam can even sit powered off for most of the day, and just be activated long enough to grab an image of the dials.

  • by bugg ( 65930 ) on Wednesday November 12, 2008 @05:23PM (#25738895) Homepage
    Often the meter supports some sort of data export mechanism, and you just need to tie into it. Hacker extraordinaire Poul-Henning Kamp did this with his gas meter. []
    • My electric meter (and most everyone else's by now) uses pulses of IR light. The transmitter is either pointed upwards, or out the face. The blink pattern is very simple to decode; it's basically 1 blink per energy unit (I forget how much.)

      I have a wireless power meter I bought through the power company which uses the blinks to show me how much energy I'm using. The only downside was that it was a royal, complete, and total fucking pain in the ass to get the receiver's sensor positioned correctly. The

  • The labor costs of checking meters is pretty significant to utility companies. One thing many municipality companies are trying is WiFi enabled meters that will report consumption to a meter truck as it drives down the street, saving hours apon hours of labor every day.

    I haven't tried to tap into my own meter, but if they can read it, with sufficient time and effort I'm sure most of the readers of /. could read it as well.


    • saving hours apon hours of labor every day

      Unfortunately, the Grammar Nazis shall never be able to share in this victory.

      • by RingDev ( 879105 )

        Heh, nice catch. I think I actually wrote that, went out to a meeting, then came back, saw the post waiting and hit the submit button with out re-reading it.

        If you think that is bad, I totally slaughtered the english language in another post today that was interrupted by a bagel break.


    • Re: (Score:3, Interesting)

      by jkerman ( 74317 )

      they are wireless, but not wifi

  • I don't know if it is possible but can a ammeter that just goes around one of the conductors be adapted for this purpose? I used to work in the plating industry and we had something we called tong testers. It measured the amps at various points in the system. The beauty was that there was no physical connection with the conductors (I think it measured the magnetic flux that was created.). It might only work with DC. I am sure that there are some electrical engineers that know about such devices. What

  • by YrWrstNtmr ( 564987 ) on Wednesday November 12, 2008 @05:55PM (#25739299)
    Since you are talking about a webcam, that currently means USB. Your spouse will likely throw a fit about yet another set of wires trailing around the house. So unless you intend to splash out for a fully wireless (and expensive, in cost and 24x7 power) camera setup, my suggestion is to abandon this idea completely.

    For the sake of your family sanity.

  • Yes, it's windows only but it works wonders: [] Point a webcam at it and use this for the vision processing.
  • by kebes ( 861706 ) on Wednesday November 12, 2008 @06:07PM (#25739467) Journal
    The image analysis question is interesting. You are trying to read dial positions, so conventional OCR is probably useless (unless there is a package to do exactly that?).

    What you can do is use image processing commands (in your favorite programming language; a shell script, Python, etc.) to crop the image to generate a small image for each dial. Then convert to grayscale (and maybe increase the contrast to highlight the dial). To then calculate the preferred orientation in the image, you calculate gradients along different directions. There will be a much higher value for the gradient along directions perpendicular to the preferred axis. This procedure is described very briefly in this paper:
    Harrison, C.; Cheng, Z.; Sethuraman, S.; Huse, D. A.; Chaikin, P. M.; Vega, D. A.; Sebastian, J. M.; Register, R. A.; Adamson, D. H. "Dynamics of pattern coarsening in a two-dimensional smectic system []" Physical Review E 2002, 66, (1), 011706. DOI: 10.1103/PhysRevE.66.011706 []

    This is easiest to do if you use a graphics package that has directional gradients built-in (but coding it yourself probably wouldn't be too hard). Basically you create copies of the image and on one you do a differentiation in the x-direction, and for the other one a differentiation in the y-direction. Let's call these images DIFX and DIFY. Then you compose two new images:

    Then you calculate a final image:

    (All the above calculations are done in a pixel-by-pixel mode.) The final image will have an angle map (with values between -pi to pi) for the image. It should be easy to then use the avg or max over that image to pull out the preferred direction. You may also improve results by tweaking the initial thresholding, or by adding an initial "Sharpen Edges" step, or by blurring the NUMERATOR and DENOMINATOR images slightly before doing the next step.

    In any case, the above procedure has worked for me when coding image analysis for orientation throughout an image (coding was done in Igor Pro [] in my case). So maybe it is useful for you.
    • Another approach:

      Let f(theta) be the function that, given the dial angle, outputs an image of the dial with the dial at that angle. Since it's easy to generate images with code, this isn't particularly hard. Then, simply estimate df/dtheta by finite differences and perform gradient descent (or use Nelder-Meade). It's possible that you'll need a good initial guess for this to converge. However, once you have this guess, then provided that the dial moves slowly relative to the framerate, each previous fra

  • Here's a crazy idea: TURN OFF THE CAMERA AND COMPUTERS!!

    Seriously, is it really that hard to read the meter every once in a while?

  • Here is my take on this ... for what it's worth.

    Rigidly mount the camera in front of it, and use some constant lighting. You want everything to be the same. Note that the light can be off, except when you want a reading.

    Take a bunch of baseline readings, as many as possible. Combine these using Gimp or Photoshop to edit out the dial needles (assuming analog needles). If your meter is anything like older US meters, the needles on the left will hardly budge. No problem. Ignore the left-most digits and co

    • by harrkev ( 623093 )

      Hmmm. After thinking about it a bit more, I have an easier idea. I will describe by example.

      For a particular needle, you know that its center is at (x,y). Have a "for" loop go around the circle (say 5 degree increments) and look at (x+20sin(d), y-20cos(d)) where "d" is the angle, and 20 is the number of pixels away to look (depends on the size of the needles and the resolution of your camera). Try to determine if the needle is present or not based on intensity (simple threshold should be enough). When

  • Once you have your OCR working, I think you should use a database to store the data, not a OO Spreadsheet.

    sqlite might be the easiest.


  • I have a problem with the premise of your question - how would this data help you? Obviously, it could tell you how much you're saving, but whether or not you're being efficient is simply a factor of how many things you have plugged in at a time.

    This method also won't tell you which devices/appliances are the ones sucking the most juice. This is where a Kill-A-Watt can come in handy.

    I recently trimmed my energy usage by:

    -dialing up (or down) the thermostats - a/c, water heater, fridge
    -switched to CF light b

  • Mechanical? (Score:2, Informative)

    Mechanical or Spinning disk type meters can be read optically or magnetically, or if you have a dig meter with LED interface you can monitor the LED frequency; Both allow for real time monitoring of your homes load. Monitoring the aggregate by collecting at all load points would be better, but that's a bit more complicated. try: [] ...for a head start. SLR-
  • Buy a killawatt or any other watt meter. []

    I found out that all of my speakers (computer speakers / external tv speakers) drain 5 watts when they are off (but pluged in). I through them on a power strip. It is not much, but everything adds up.
    With 2 sets of speakers: .14$/kWh * .010kW * 24h/d * 365d/year = 12$ a year

  • From looking at your image, this doesn't seem like it should be very difficult to implement, unless you want extreme precision on the 10's dial. The dials themselves aren't moving, and you don't need to actually read the numbers. You just need to know where the tip of the needle is, then use that position relative to the center of the dial to get a reading. The first thing I would do is subtract the background. Use a couple different images to patch together a "background" image, where the needles are miss

  • Of course others pick the solutions like momentum comparisons, directional gradients and so on. They are very nice mathematically and elegant solutions, but... DAMNED UNRELIABLE. They work very well in theory. In practice, you spend 90% time fighting white noise, 9% replacing computationally intensive algorithms with predefined results, and 1% by doing solid (but rather simple) maths to get the final result.

    Oh, and second that much to get image from the camera into a format where you can read or set value o

  • How much energy does it cost to keep this exercise running? Was it worth getting a webcam and keeping a computer running for something that you can check yourself in seconds?

    Just a thought.

  • How long will it take you to complete this project? How many times could you walk to the basement in that amount of time?
  • If you can get access to the meter hands, then you could put a red blob of ink at the end of the hands, and a blue blob in the centre. This would make determining the angle of each of the meters much easier.

    To do this you could use simple image processing tools to guillotine the image up into the respective meters. Then find out the pixel location of the blue and red blobs by filtering out just those colours. From these two x/y pixel locations you could use simple trigonometry to calculate the angle.

    If you

  • You have known lighting conditions and a strictly limited camera orientation and object configurations.

    You can take the inverse of the pixel values as they would be if the hands weren't there (you can mock up the pixel values under the hands by hand since you only need an approximate inverse of the background plate). Then you add that inverse to an image and threshold to get black hands on white background.

    Now you can use a hough transform to find all potential hands and you know the locations of the centre

    • by Bloater ( 12932 )

      You might want to blur the image (and blur the inverse). This will allow for minor camera pan or rotation but you'll need a fairly high threshold. The thickness of the hands determines the blur kernel size and just how high is the threshold.

  • Lots of folks have suggested methods for developing an algorithm so I'll point you to some software that is free and very powerful. ImageJ is funded by the National Institutes of health, it is freely available and more than capable of the degree of image analysis you'll require. As others have mentioned image quality and consistency can be a huge hurdle so make life easier by setting everything up with care.
  • You're making this far too hard.

    The way to do this is to use a split-core current transformer. [] You need two of these, one for each hot lead coming into your house, usually placed after the main switch. They clamp around one conductor of the power cable, but don't contact it, so they're safe. Out comes a voltage from 0-5V, proportional to the current. You can wire them in series, to get a single signal (phasing matters). Run the output (which is AC) through a full-wave bridge, and put a capacitor of a

  • The total power usage of your house gives you no clue of what the biggest contributors are, unless you're prepared to spend a few weeks running only one appliance at a time. This data would only help to see if the energy-saving measures you're taking have worked.
    Get a Kill-A-Watt and take some time to learn the characteristics of your appliances. The even simpler approach would be to read the appliance's type plate or manual. Hell, any website on in-house power usage will have a list of the biggest power ho

  • The meter gauges look identical to the ones in the U.S., so if it's read the same way, all you need is a program to analyze a piece of a photograph for presence or absence of an image.

    In the U.S., the rule is 'read down', if a needle is between two numbers you count it as being as the lower of the two. If it's on the number line then you count it as that.

    The example picture shown is read as 375,064.4; I originally wasn't sure whether the segment I read as 5 (because the needle was very close to but I wasn'

"So why don't you make like a tree, and get outta here." -- Biff in "Back to the Future"