Part 2. Wii Balance Board Scale
A compact refrigerator sitting on top of a Wii Balance Board
The first step of this project is to find an easy, reliable way to detect how many bottles are in our refrigerator. If we assume that only bottles of the same type are inside the refrigerator, then we can use a scale to weigh the refrigerator and all of its contents. Once we know the weight of the refrigerator and the weight of a bottle, simple math will tell us how many bottles are present.
We need more than just a scale. We need a scale that we can control and read with a single-board computer like a Raspberry Pi. We need a scale that is either always on or turns on automatically on command. We need a scale that will fit neatly under our refrigerator without sticking out but has enough surface area to keep the refrigerator balanced and not wobbly.
The Wii Balance Board is almost the perfect solution (with two simple tweaks that we will discuss in a bit). Measuring in at 20.44" wide by 12.44" deep, the surface area of the Board fits nicely under a compact refrigerator, which typically measures 21.5" wide by 24" deep. Ideally, we would have a scale that is identical in width and depth as our refrigerator. The surface area of the Board provides just enough stability to work. The Wii Balance Board has a weight limit of 330 lbs, more than enough for a compact refrigerator full of beer/wine bottles.
The Wii Balance Board uses bluetooth for all communications. We will just need a bluetooth adapter plugged in to our Raspberry Pi and a little Python magic to control it.