BUILDING A digital scale FROM scratch
[Raivis] was given a particular task at his university – find a way to measure how numerous Duplo bricks are stacked together. There are a number of ways to do this, everything from computer vision to using a ruler, but [Raivis] chose a much much more educational method. He built a digital scale from scratch out of a strain gauge and a Wheatstone bridge. The build log is immensely educational and offers some insight into the challenges of weighing things digitally.
A strain gauge is a easy piece of equipment, just a small force sensitive resistor. When attached to a metal bar and a force is applied, the resistance inside the strain gauge changes, but not by much. There’s only a few micro Ohms difference between the minimum and maximum of [Raivis]’ load cell, so he needed a way to measure very small changes in resistance.
The service was a Wheatstone bridge, or four resistors organized in a square. When one of the resistors in the bridge is replaced with a strain gauge, very small changes in resistance can be measured.
With a customized ‘duino amplifier shield, [Raivis] can measure the resistance of his load cell with 10-bit resolution, or a maximum weight of 1.32 kg with a resolution of two and a half grams. A single duplo block weighs about 12 grams, so we’ll call this one a success.