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[Reply #15 on:]

7106 chip having 200mV or 2V full scale and not 0-5V range at pin 31.

All you circuit are "LIVE", make sure not connect to computer USB if you connected it to your arduino analog input. if you do, it may damage your computer.

[Reply #16 on:]

For the lower ac voltages (like 125vac) and the multimeter one might be able to use a small isolation transformer like below for the multimeter connection to the ac. Another issue would be to set the reference voltage on the arduino to 2v to get full reading range capability. Not sure how easy that would be.  

http://www.radioshack.com/product/index.jsp?productId=2103994

[Reply #17 on:]

It would definitely be best to get an isolation transformer made for ac line conditions, as the nominal ac voltage is usually an average value and not the peak voltage encounered.

[Reply #18 on:]

I would like to know if anyone knows where transformers can be had(for medium to high power applications) for less than a small fortune. I've also heard of toroids that you can wind yourself, but what if you need 20A @ 100V for a DC supply?? This should probably be its own thread, but I'm lazy. I would REALLY APPRECIATE any advice on this.

One could relatively easily wind a multitap transformer so they could have a selectable ranges of AC measurement voltages (10V,100V,1000V...). Perhaps not.  

[Reply #19 on:]

Are the transformers found in microwave ovens easily re-wired? I'm not sure if it works this way, but those things can be rated for upwards of 1500W. I'm sure that they are wound for a different voltage, though. I don't know much at all about magnetic flux density/saturation...stuff. All I have learned about that stuff is the effects of fields on charged particles (not really pertinent to transformers) and electronics.

Question: If you have a toroid(or whatever) with a 20-turn primary winding and a 10-turn secondary.. Is it the same as a 200-turn primary with a 100-turn secondary? Is there a trade-off? How do you choose the number of windings?

pat

[Reply #20 on:]

I will only be measuring mains, 50-60 Hz only, 115-1-60, 220-1-50 and 230-1-60.

[Reply #21 on:]

How about using a wallwart, linear type not switching then maybe a resistor divider on the secondary output.

Similar to what these guys did.

http://www.itwatchdogs.com/product-detail-city_power_monitor-20.html