> Sense resistor, hall effect sensor, or something like that.

I saw the allegro micro hall effect device. That is for way more
current (50A) and might not measure small current values accurately.

> You won't be able to measure 20A directly.

Actually I have to measure current in two different apps. So I was
thinking if only one front end would work. Anyway I can go lower to
0-5A.

 
> 1 ohm gives you 1V at 1A, and dissipates 1W.
> 0.1 ohm gives you 0.1V at 1A, and dissipates 0.1W
> If you can tolerate the 2V forward drop, then this would scale pretty well to a 2.5V input range ADC.
> If you have to take the current sense resistor smaller, then you'll need an op-amp to bring it back up.

So if I use a 1 ohm, ground line sense resistor, I can get a 0-5v (for
0-5A) across the resistor and PIC16D876 ADC can measure that range!
Right?


 
> Alternately, Maxim makes current sense chips that integrate the amplifier.
> They can solve any $0.50 problem for only a few dollars. :)

That is true :-) One of my friends at Linear suggested me to use
LTC2433-1 as he wrote a design note for linear "DN341". I don't like
that idea as that is an added external component.


Regards,

Chetan Bhargava
www.bhargavaz.net
_______________________________________________
http://www.piclist.com
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist