Digital scale / relay activated?

Hi all.
I have a ultra precision digital scale that I want to modify to activate a relay when it reaches a preset weight. I want to adjust the weight if necessary with say a pot.
Can you supply me with a circuit if possible.
The scale is manual fed at the moment but I would like to install a small dc motor to do it and the relay must disconnect it if a certain weight is reached.
Thanks.

Before we can start to help you must give us much more detail.
What is the product number/type of the scale?
Do you have the type numbers of any/all IC's inside it?
Can you give a link to the datasheet(s) of the scale and its components?
What is the purpose of the motor?
What type of motor? Volts? Current?