Tweet-A-Watt directly to arduino serial instead of xbee to c

XBee projects like the adapter, xBee tutorials, tweetawatt/wattcher, etc. from Adafruit

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dbasner
 
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Tweet-A-Watt directly to arduino serial instead of xbee to c

Post by dbasner »

Hi,

I built the kill-a-watt side of the tweet-a-watt project and was wondering if I could bypass some wireless issues I was having by just hooking the signal leads into pins on an arduino. I know since the way the xbee works is over the serial port that they should probably go into the TX and RX pins, but beyond that I am unsure how to use Serial.read() on the arduino in order to read in the voltage and amperage data from the kill-a-watt.

What pins should they go into, and how should I grab that data on the console side?

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adafruit_support_bill
 
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Re: Tweet-A-Watt directly to arduino serial instead of xbee

Post by adafruit_support_bill »

That would be quite dangerous. The Kill-A-Watt analog signals are collected by analog pins on the XBee and relayed to the second XBee. The problem is that there is no true ground in the circuit. The XBee communication is safe because it is wireless, running any wires out of the Kill-A-Watt enclosure would expose you to dangerous line-voltages.

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Deadboy
 
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Re: Tweet-A-Watt directly to arduino serial instead of xbee

Post by Deadboy »

What do you mean by "true ground"? I've heard this referenced before but no explanation given.

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adafruit_support_bill
 
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Re: Tweet-A-Watt directly to arduino serial instead of xbee

Post by adafruit_support_bill »

Voltage measurements tell you the difference in electrical potential between two points. Neither of those points is necessarily at "earth ground" potential. One could be at 119v and the other at 120v relative to earth ground, but your meter would read 1v. If you were touching something that was grounded to true earth ground (most any metal electrical appliance) and touched one of those points too, you would get a nasty shock at least.

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Deadboy
 
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Re: Tweet-A-Watt directly to arduino serial instead of xbee

Post by Deadboy »

Ah, I see.

So, how did this guy do it? http://matthiaslee.com/node/49

(Just curious. I'm not attempting this.)

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Re: Tweet-A-Watt directly to arduino serial instead of xbee

Post by adafruit_support_bill »

We may never know. As the author says:
I am purposely not handing out a schematic to ensure only people that know what they are doing attempt this. If you screw up, you could fry your computer, yourself or others.
One forum member has implement an optically isolated version. The details of that are posted in the forums somewhere.

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