Designing a solution so I don't have to sleep plugged into the wall.
Skills: KiCad, Fusion 360, PCB design/layout, FDM 3D Printing
I have Type 1 diabetes and wear an insulin pump. It's a great device, but I really hate charging it. I used to use an older insulin pump which took AAA batteries, although this one is rechargeable through Micro USB. This is great to cut down waste and means I don't have to go look for a battery, but it does make charging inconvenient as I still need to be plugged into the insulin pump while it charges. People suggest charging the pump while it is removed during showers or overnight, but I am usually in a rush and don't like sleeping plugged in. I had had success in the past charging my pump using a small portable charger, although it was still quite bulky.
There are phone cases with built in batteries, so why not for insulin pumps? I knew I wanted the batteries to be hot-swappable, so the case would always stay on the pump and I could just pop a new battery in when the battery started getting low. I originally planned to use a AAA battery as its small size fit well with the pump, although it didn't have a ton of capacity. More importantly, I needed to boost the 1.5V up to the 5V the USB on the pump required, resulting in insufficient current. As a result of this, I decided to switch to use a 10440 Lithium Ion battery. This is the same size as the AAA, but gives 3.7V.
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I learned to use KiCad for this project. I spent a lot of time working with different layouts and managed to fit it on a 2 layer board. While the idea behind the project was to hot-swap the batteries, I also wanted to be able to charge the pump through the external battery directly in case I didn't have a spare battery ready. For this I added a Micro USB port to match the pump, but also added a USBC port as there was room. It wasn't necessary but it certainly would add to the convienience.
I ordered the PCBs and soldered the components on. I designed the PCB to accommodate a 10440 battery holder but also a 16340 battery, which is commonly used in flashlights. The shape is less ideal, but they are manufactured with built-in charging ports sometimes so I figured it was a good idea in case I wanted to pivot in the future. The board also has status LEDs that indicate the battery state.
I used Autodesk Fusion 360 to design the housing. It was an iterative process with each prototype better than the last. The case is in two parts, with one housing the battery and board and the other retaining it onto the pump. The two pieces snap together, and the battery can be swapped with the case in place, as can the insulin reservoir.
A challenge with the case was ensuring that the battery section wouldn't snap off while keeping the insulin reservoir accessible through the case. The cutout on the bottom to allow the reservoir to be accessed means the case is too thin to add the snap to connect the sections in that area, so I couldn't just move the joint in that direction.
I solved this challenge by offsetting one of the snaps but not the other, making the joint between the two pieces at a diagonal. This solved the problem and resulted in an extremely rigid assembly.
I'm overall very satisfied with this project so far. I use it often and it works quite well and as intended. That said, there's more work I would like to do on it. I incorrectly set up the traces for the USBC port which resulted in a short and a fried IC, so I had to remove the USB and stick to the Micro USB. I would like to fix this as well as add a cut off that shuts of current flow to the pump to help prevent damage to the external batteries by driving them too low on charge. I will probably get around to it at some point, but for now I'm super happy with what I was able to bring from an idea to reality in a couple of months.