Help Needed with Load Cell Project and Op Amp gain configuration OP07/TL081

[neddie]

Just to add to the post , don't forget you can easily generate a negative rail for your op-amp via one of the micro pins , 2 caps and 2 diodes. With a 5V micro you won't get -5V , but you could easily get -4V. That would be more than enough and it takes away any funny biasing headaches.It will also make it easier to get things going as expected , and then you can do the single supply thing once you have and other issues sorted out.
Neddie

 

[??????????????? ?????????]

i am using lm358 for 20kg loadcell
very linear compared to op07
want to get the gain for 5gms
no i am getting 473-475 for no load
475-476 for 25gms(this is the minimum, i get).

 

[Audioguru]

You did not follow the given advice. Your resistor values in the opamp differential amplifier are MUCH TOO LOW! The 1.5k resistors should be 15k or 150k and the 1k resistors should be 10k or 100k.

Look at the datasheet of the opamp you are using. The inputs of an opamp in an LM358 have a working range from 0V to 1.5V less than the supply voltage. The output voltage swing is from about 0.1V to about 1.2V less than the power supply voltage if there is no load.