Approach

Design approach

Magnet size: We decided that the device needed to be big enough for Viha to see the neopixel color feedback clearly, but small enough to still feel like a magnet. 

Size of neopixel: It should be big enough so that Viha can see the colors clearly close up as well as when she is 80'' away (glancing at the fridge on her way out the door). 

Visual design of the milk carton: From observing the items Viha has in her room, she likes objects that are cute and animated-looking. This inspired us to take on a cartoon-y aesthetic for the visual design of the milk carton. 

Engineering approach

To enable the fridge magnet to detect the milk, we used a bar type load sensor. The load sensor with a maximum rated capacity of 5 kgs was chosen as a typical one gallon milk carton weighs at around 4.3 kgs. To detect the level of milk in the fridge, the sensor reads the instantaneous value every second and publishes that to the cloud. The fridge magnet subscribes to the event and sends signal to the neopixel to display different colors as mentioned in the schematic diagram as shown above. A 1200 mAh LiPo battery is connected to the neopixel circuit.