To begin making our milk scale we first made a 3D model of what we wanted the scale to look like on Rhino and started to think about how we would design the electronics as well.  We started off learning about the basics of Arduino’s and then took the knowledge we had learned and began to apply it to our milk scale. We started experimenting with pressure sensors we could to use to create the scale. We originally thought we would use four pressure sensors in each corner of the scale. The tricky part was we could not get the pressure sensors to work correctly or accurately enough. We thought about hacking an actual scale, but ended up deciding against it.

We were having a hard time getting the pressure sensors to work so we briefly considered a different design that would avoid the pressure sensors all together. This design would use springs and a lever. The springs would hold the top layer of the scale up and adding weight on the springs would compress and push the lever down. We could then tell the weight of the milk by how far down the lever went.

Ironically as soon as we started to model the new design we got the pressure sensors to work with the old design. The problem was we were plugging the pressure sensor in through a breadboard, which shouldn’t have affected it, but it did. Now that we had the pressure sensor working we decided to go back to our old design.

We figured out that to get the pressure sensors to work we would need to sandwich them between two pieces of double-sided tape. The pressure sensors only work when something squishy is pushing them down.

We also cut out the main pieces of our scale. It is made up of two pieces of plywood, one on the top and one on the bottom. In between the plywood are eight plywood circles. Four circles are glued to each corner of the plywood halves. In between the circles that sandwich together there will be the four pressure sensors; one in each corner. Then the wires will go into a box with the Arduino and all the electronics.

We have it working! … Well kind of. For starters it turns out we will only have access to one pressure sensor so we’ve moved it to the center of the scale. We put  all the pieces together and spray-painted the wood pieces, because it has to be stylish, of course. Once the paint was dry we glued the feet to the top and bottom, then we put the top and bottom together with the sensor sandwiched in between the pieces. Then we hooked up the pressure sensor to the Arduino and put some basic example code on it. We were able to get a reading from the scale, and could tell that the sensor was working. The problem is that the pressure sensor wasn’t give out the most accurate reading.

We then decided that although an accurate reading would have been nice, we didn’t actually need an exact reading. You don’t need to know exactly how many ounces of milk you have, just the gist.

We put together our milk scale again and decided to redesign.  We decided to make a box for the electronics and Arduino. We made another layer to the scale and hid the electronics in that compartment. It makes it look a little chunky, but it makes the most sense right now. We made the compartment with a bendable plywood design. We also switched over to the Arduino Yun, which is the wireless Arduino. We had a little difficulty getting it to cooperate properly but we got it to transmit the data wirelessly.

We have the milk scale set up so that you can read the date from the Onion’s network. We also have it set up for push notifications to your phone when you need milk. It works!