I've been trying to make a wattmeter using arduino but cannot find the shield I need to buy to put onto my arduino to make it. There are no such parts in the Arduino Store and online the best I could find is this. This measures the arduino's energy consumption, however, not other things. I am really new at this and thoroughly lost. I would be really glad if someone could help me with this problem :)

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    i've built a ton of "things", but i've never used a shield; don't be limited by less than your imagination. the next-simplest is to look for "modules" aka "bricks". there are plenty of Hall-effect based current sensors on ebay, and voltage just needs a few resistors to measure. – dandavis Apr 3 '17 at 17:25
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    Where did you get that the linked shield only measures Arduino's energy consumption? It is clearly stated that it connects up to three AC current sensors. – gre_gor Apr 3 '17 at 17:27

You will need an Ampere meter and a Voltmeter. Watts is Volt * Ampere.

There are logic level compatible units out there for ampere meters ranging from a few mA to at least dozens of Amperes.

Also for voltmeters there are several logic level compatible units available, to plug in your project.

The rest is math. (Watts = A * V )

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    P=VI for DC, or for AC with a purely resistive load. For AC with other kinds of loads you should include the power factor. – Majenko Apr 3 '17 at 20:18
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    Yes, that's perfectly true. I just assumed, it'll be DC. – ansi_lumen Apr 3 '17 at 21:17

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