ok so i have just started to design a circuit that will display me the total watts my pc is using every 1 second. Now the way i think of doing it is, to get some kind of current measuring device and taking the ouput of that device to a microcontroller and just simply multiply it by the voltage that comes out of the plug in the wall?

Will my idea work or not
Critisism is apreaciated.

 

To measure the DC current you will need to put a resistor between the power supply and the PC. This is not a good idea because it will drop voltage, make regulation poor and dissipate power. Another idea is to use a current transformer to monitor the AC input current and multiply it by the grid voltage. In this way you will get the total input power to the PC power supply (power used by PC + power losses).

Why do you need to monitor the power?

 

just because i want to create stuff for myself that i can use , and i always wanted to see the total watt's my computer use...

 

If you are a beginer this is not a suitable project to do. Make something safer and which does not has the possibility to harm your PC. If you want to see the power consuption of your PC buy a cheap wallwart wattmeter.

 

There's a commercial device called a Kill-a-watt that measures voltage, current, power and so on. And there's a hack online to modify a Kill-a-watt to transmit info wirelessly. That's the easiest, cheapest and safest way I can think of to accomplish your goal with a little bit of tinkering. (Of course, fiddling around with line power at all is dangerous. But you know what they say: good judgment comes from experience. And experience comes from bad judgment!)

http://www.ladyada.net/make/tweetawatt/

 

The problem is more complicated than it appears and, if you're a beginner, stay away from working on AC line voltages. The suggestion of a Kill-a-Watt meter is a good one and it will tell you what you need to know. When I bought mine, you could find them on the web for $20 or so.

The proper way to make this measurement is to display the current and voltage waveforms on a scope, then multiply them together to get the instantaneous power. Then the power waveform needs to be integrated. If you simply measure current and voltage e.g. with a DMM, you may get the wrong results, as I learned years ago on some early PCs -- they had a significantly nonunity power factor.