small dc signal amplifier schematic need

[mistergh]

My favorite Op Amp for those applications is the TLV2470 from Texas Instruments. This is a rail-to-rail unit and almost indestructible. The input impedance is in the Meg Ohm range and the output is a few ohms max. You can drive an ADC directly with it.
You can find a simple gain calculator at this address:
http://www-k.ext.ti.com/srvs/cgi-bin/webcgi.exe?Company={5761bcd8-11f5-4e08-84e0-8167176a4ed9},kb=analog,case=obj(32618),new
A calculator for gain and offset is here:
http://www-k.ext.ti.com/srvs/cgi-bin/webcgi.exe?Company={5761bcd8-11f5-4e08-84e0-8167176a4ed9},kb=analog,case=obj(35457),new

Good luck!

[mikendee]

Robert,
For amplifying the output of a load cell I think you should use an instrumentation amplifier. I have use an INA114 in a situation like yours. You can buy a descrete chip or you can construct one with 3 op-amps an some resistors.
The fact that the output voltage goes down as the weight increases maybe fixed by swapping the excitation voltage or turning the load cell the other way up. If not it shouldn't be hard to fix it in the software.

Hope this helps.
Mike