AVR-Chat

--- In AVR-Chat@yahoogroups.com, Zack Widup <w9sz@...> wrote:
>
> 
> This is all very fascinating.  I have had it in my mind to some day 
build 
> something like this just for fun:
> 
> http://www.westmountainradio.com/Whattmeter.htm
> 
> I figure I can put something together for far less than the cost of 
this 
> unit, without the need for all the bells and whistles or extreme 
accuracy.
> 
> Zack

Heh... if you noticed, "Current is measured on the negative lead" - 
they're not doing any of the common mode stuff.

As far as accuracy goes, the number of bits really determines your 
range (ie, if you want to measure 1mA quiescent current, along with 
1A surge currents, you need >1000 counts, so at least a 10 bit ADC).

Of course, I think you need to know the frequency response too... we 
had a guy measuring uC power usage using a DMM... the result was 
ungood.

-Thor

 
> On Tue, 31 Jul 2007, Ned Konz wrote:
> 
> >
> > There are a number of current-sense amplifiers that do level 
shifting
> > from high voltages.
> >
> > For instance,
> > http://www.linear.com/pc/viewCategory.jsp?
navId=H0,C1,C1154,C1009,C1077
> >
> > shows a table of Linear Technology's "current sense amplifiers".
> >
> > They have two parts that should do the job (they'll go to 100V
> > common-mode voltage):
> >
> > LT6102HV
> > http://www.linear.com/pc/productDetail.jsp?
navId=H0,C1,C1154,C1009,C1077,P38188
> >
> > LT6101HV
> > http://www.linear.com/pc/productDetail.jsp?
navId=H0,C1,C1154,C1009,C1077,P12995
> >
>