Now that my Dog Bed Weight Scale is sending data, I’m going to have a go at a water bowl scale. The idea is that, like the bed, the bowl will periodically send its weight to a cloud. This data should tell me when Pippa drinks, when we refill her bowl, and (maybe) how much she drinks.
The work-in-progress sources on Github, contain the beginnings of the Arduino 101 Sketch, Bill of Materials (Parts List), mechanical design/construction details, and a day-by-day project diary.
Since I was already familiar with Sparkfun’s Load Cell Amplifier, I only needed to pick a Load Sensor/Cell. I decided to go with their 10kg bar Load Cell because it should be easy to mount as a single-point weight sensor, and it’s relatively inexpensive.
I decided to construct the scale from 1/2-inch MDF (Medium Density Fiberboard) because it’s thick enough to minimize bending and it’s not too heavy. Although raw MDF swells and warps if you get it wet, that’s not a problem if you put a good coat of paint all over it – so I’ll be painting the parts before I assemble the whole scale.
With the major parts chosen, I sketched the to-scale wooden parts and the layout of the electronic parts.
![to-scale sketch of the scale](https://bluepapertech.com/wp-content/uploads/2023/04/20160720_194043Bwiki-768x576-1.jpg)
I then cut the MDF pieces and bored the access hole that will let me assemble the last of the parts.
![Cutting the access hole, using a Forstner bit](https://bluepapertech.com/wp-content/uploads/2023/04/20160720_202247Bwiki-768x576-1.jpg)
I then test-laid-out the parts on the bottom plate of the scale. Doing that reminded me that the assembled scale needs a way for a USB or power cable to get out of the scale. I decided to probably cut a diagonal channel in the bottom plate to allow for a cable – if I’d put the Arduino 101 where I initially planned to put it, the USB cable shroud would be in the way of the lid.
Note: the lid includes a water curtain on its sides, which needs to overlap with the edge of the bottom plate to keep spilled water from getting into the circuitry.
![Rough layout of parts. Note the space required for the USB cable](https://bluepapertech.com/wp-content/uploads/2023/04/20160720_204832Bwiki-768x576-1.jpg)
I then used a drill press to drill the holes for the mounting screws and counterbore the holes for the nuts on the bottom.
![I counterbored holes for the nuts](https://bluepapertech.com/wp-content/uploads/2023/04/20160724_095622Bwiki-768x576-1.jpg)
The next step was to make the connectors for the circuitry. I probably should have soldered thicker wires (an inch or so in length) to the Load Cell wires, because the Load Cell wires were too thin to crimp connectors onto – the Load Cell wires are very fragile.
![Ready to crimp connectors onto the Load Cell wires](https://bluepapertech.com/wp-content/uploads/2023/04/20160724_100559Bwiki-768x576-1.jpg)
Because there’s only one Load Cell, and because it connects directly to the Load Cell Amplifier (unlike the half-load-cell Load Sensors I used in the Bed Scale), the circuit is pretty simple.
![The assembled circuit (awaiting Load Cell mechanical parts)](https://bluepapertech.com/wp-content/uploads/2023/04/20160724_113225Bwiki-768x576-1.jpg)
I’ve ordered parts from McMaster-Carr to mount the Load Cell to the top and bottom of the scale. That mounting will look a lot like the Two Plate Configuration shown in Sparkfun’s Load Cell Amplifier Hookup Guide, except that my scale will have a lip fastened to the top plate to keep spilled water out of the electronics.
In my next post, I finish the woodworking… with some surprises.