You can build a dc active current sensor using a GMR and a differential
amplifier.  Sensitivity can be improved by wrapping turns under the GMR.  I
used multiple small traces.  Bandwidth is primarily a function of the diff
amp.

-----Original Message-----
From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu]On Behalf
Of Chen Xiao Fan
Sent: Sunday, February 05, 2006 10:23 PM
To: Microcontroller discussion list - Public.
Subject: RE: [EE] scope current probes



> -----Original Message-----
> From: piclist-bounces@mit.edu
> [mailto:piclist-bounces@mit.edu] On Behalf Of Gerhard Fiedler
>>> What it your requirement for the current probe?
>
>> 5mA to 1A or so...
>
> Don't you need a few different sense resistors for such a
> range? Hm, maybe not... 1 ohm/1 W may do it. But for the low
> currents, a  higher resistor would increase the SNR.

I think the OP does not want to use sense resistors and he
wants to use something with the features of those expensive
TEKtronics current probe and amplifiers but within US$100
budget. Other than the cheap sense resistors, I think it
will not be easy to use CT (current transformers) and Hall
effect sensors and some other current sensing elements to
achieve 1mA resolution cheaply. I remember the old TEK
current probe/amplifier set I used before can not achieve
1mA resolution.

Regards,
Xiaofan

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