You can just buy strain gauges which are specially cut copper foils on a thin plastic substrate that you glue to something, like a metal strip. The resistance changes very slightly as the metal bends.
You measure the change in resistance with a wheatstone bridge tuned correctly.
You basically just need a strain gague (a few dollars), 4 resistors, an op-amp, and a microcontroller with an ADC.
Calibration is important and you'll run into things like the metal bar creeping, permanently bending as a result of weight being put on and off.
You measure the change in resistance with a wheatstone bridge tuned correctly.
You basically just need a strain gague (a few dollars), 4 resistors, an op-amp, and a microcontroller with an ADC.
Calibration is important and you'll run into things like the metal bar creeping, permanently bending as a result of weight being put on and off.
But also, milligram accurate scales are $20 on Amazon https://www.amazon.com/GRAM-PRES-Precision-Milligram-Reloadi...