Scale with switched output

I would like to build a scale that would- be able to be programmed with a specific weight (say 1/2 oz) and then when putting items on the scale and reaches the programmed weight (1/2 oz) it would switch an output to control an external device.

Any suggestions?

Steve

Most problematic is the mechanical construction. Once you can get the correct weight, you can compare it against the given limit.

That is fine.
I don’t know what kind of sensor to use for weighing.

Steve

If you want to make it all yourself, you need 4 strain gauges, placed under the 4 corners of the platform, Wheatstone bridges and amplifiers, and external high resolution ADC with 4 channels.

It's much easier to hack a cheap kitchen scale, as discussed in many threads in the forum and on the web.