The Box

This week, our team shifted our design plan. Instead of using a thermos, lunchbox, or other pre-made container as our heating chamber, we decided to build our own.

This is the first prototype of our two-chambered device. The smaller section (front) is the heating chamber, and has insulation and a reflective surface to avoid heat loss. The thermistor and heating pad wires go through a small hole in the divider into the larger electronics chamber (back) which is not warm. We settled on this concept because it seemed like the easiest to make open-source as well as the most customizable.

Making this prototype was an interesting process. First, we needed a proof-of-concept to see if something like this could even retain enough heat to be effective, so we ran a few tests with a box made entirely of the purple insulation above. It worked, so we moved on to the laser-cut version. We started with an online box maker and then proceeded to make additional adjustments to add in the barrier in the middle. Then we cut it and began gluing the box together. Only the front and back panels are removable ‘doors’–– in the end the top was glued on as well. When we first opened up the wood glue, there was a sort of film of dried, yellowing glue blocking the tube, which was dubbed the ‘glue monster’.

After the prototype was fully assembled, it became clear that the electronics chamber is much larger than necessary. In our next iteration, we plan to make a ‘stacked’ design, where the electronics chamber is on top of the heating chamber and shares the same small footprint, so it is much smaller and can more intuitively be put in a bag right side up.

Electronics

The other major project I worked on this week was continuing to troubleshoot the circuit. My teammate Kenton and I began disassembling the various components––thermistor, n-channel transistor (the component that tells the heating pad when to turn on and off), heating pad, display screen, and Arduino––to get them to work separately before combining it all together again. A very helpful electrical engineering professor explained how the transistor works to us, and we realized that the wiring had previously been wrong. The heating pad worked in our tests and so did the Arduino. We had two primary ‘Eureka’ moments; one with the thermistor, which after careful calibration now reads temperatures accurately, and another with the screen, which we were able to activate for the first time on Wednesday:

Unfortunately, we were only able to get it to work with an Arduino Uno (shown above), and not with our Arduino Nano, which is much smaller, despite using all of the same pins and the same code. According to online help forums, many people have had this problem in the past, and we were unable to find any satisfactory solutions. We have a meeting with the senior design team member who previously figured out how to make it work with the Nano on Monday, but if that does not work we may need to switch to using the Uno.

Next week, we plan to reassemble the entire circuit, and if everything works properly, graduate to soldering it on a perfboard, since soldered circuits are much more permanent and no one can accidentally knock out a wire. Once this and the new box is done, our first high-fidelity prototype will be complete and we can move on to the testing and evaluating stage of the engineering design process.