Home power monitoring
Sunday, July 12, 2009
posted by Eliot Phillips
filed under: arduino hacks, home hacks
Reader [john] finished up his home power monitor over the holiday weekend. It uses a pair of current transducers clamped onto the mains. These output 0-3V and are read by the Arduino’s ADC. The Arduino averages samples over a 20 second period, calculates power used, and uploads it using an Ethernet Shield. The shield can’t do DNS lookups, so he uses a WRT54G to negotiate with the remote webserver. He admits that the system could be more accurate; it can’t detect small loads like wall warts. He also says that money could be saved by talking serial to the router instead of over ethernet. Here are the current usage charts.
You can find many power monitor projects like this in out Home Hacks category.
1 komentar:
Sorry, bull.
To quote: “when laymen hear the root “kilo” they think 1000″
That’s because that’s CORRECT. The Metric prefixes are base-10 prefixes. Period. Computer Science used these prefixes because they were close enough, when we first started using them. Error didn’t accumulate that fast when you were talking about 80 meg hard drives. However, the gigabyte/terabyte/petabyte age is here, and those discrepencies are HUGE. Metric prefixes just don’t work to approximate these higher powers of 2.
However, saying that 1 kilobyte = 1024 bytes is, in point of fact, incorrect. The metric prefix “mega” means 1000. The correct term is kibibyte – KiB. 1 KiB = 1024 bytes. The fault here is not on Apple – they’re simply calculating a kilobyte as it SHOULD be calculated. The fault lies with the computer science folks for using metric prefixes incorrectly for so long.
As for the argument that the meaning of the prefixes has changed and we should keep the status quo – what if ever field did that? What if you had to remember that 1 kilogram was really 1001 grams or 1 micromole was really .000000101? Start using metric prefixes incorrectly and you set a dangerous precedent. Why should a computer be special? Why should 1 kilobyte be 1024 bytes, but one kilo-anything-else be 1000?
So good for Apple – call things what they ARE. Use standards (and that’s exactly what they are) correctly. Use KB for 1000 bytes, and KiB for 1024. (you can control-click to get file info if you REALLY want to, just like a Windows box that tells “space on disk”)
Now, are they doing this to sell “larger capacity hard drives?” Nope. Go to ANY website that sells hard drives and look at the calculation for GB. Go ahead, I’ll wait. See where it says “1 GB = 1000000 bytes”? Hard drive manufacturers have been doing this for a LONG time now. This is SOP in hard-drive land. All this update in Snow Leopard means is that when you buy a 500 gig drive, it’ll show up in Finder as 500 gigs (OK, a little less because of formatting, but you get the picture). This in no way affects ONLY Apple HDDs – ANY hard drive will be counted in base 10. How is that a competitive advantage to their hardware sales? The only think that will happen is the “actual formatted capacity may vary” footnote will refer to the fact that the disk formatting takes some space, not the fact that disks are sold in base 10 sizes then treated in the computer as base 2.
Also, what’s up with this “Real Math” crap? What is that, other than FUD? Yes, computers operate in base 2. So? That doesn’t mean all other bases are incorrect. I guess, since base 2 is the REAL math, I’ll have to go tell all the mathematicians in the world that their work is irrelevant.
To sum up:
“the term kilobyte was adopted to represent 2 to the 10th power bytes”
This was a bad move, ignored what “kilo” meant, and should never have been done.
“doesn’t Apple have a lot to gain if all the storage-containing-hardware they sell sounds bigger than it actually is?”
HDD manufacturers already do this, as stated earlier in the summary. This point is irrelavent.
“(base 2, aka real math) … (base 10, aka fake math)”
WTF?
This article is FUD, plain and simple.
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