Go to Maxim's web site and check out the MAX471 and MAX472.

http://dbserv.maxim-ic.com/quick_view2.cfm?pdf_num=1108

It's a single supply "high side current sense" IC that outputs a voltage
proportional to the current through a very low value (0.035 Ohm) sense
resistor. The sense resistor itself is built into the IC and can handle up to 3
Amps I believe. It comes in 8 pin DIP and SO packages, so it doesn't take up
much space and it runs on microamps of supply current.

Maxim also provides some good applications notes with the datasheet. Follow
them and you should have very few problems.

Matt Pobursky
Maximum Performance Systems

On Thu, 5 Apr 2001 00:37:33 -0000, Thomas N wrote:
>Hi everyone,
>
>I am building a robot and I want to monitor the current drawn by the motor.
>The motor can draw from 250mA up to 2.5Amp!  What do I have to do to measure
>this current?
>
>I was thinking of puting a 1-ohm resistor probe in series with the motor,
>and feed the voltage drop across the resistor into a ADC, but at 2.5A, the
>voltage drops across the resistor is too high and it leaves nothing for the
>motor!
>
>Is there any current sensor circuit out there that have very low loading
>resistance?  Is there any IC doing this job?
>
>Thanks
>

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