Creating Custom Coin Cell Battery Holders for LED Sewing Kits

2024-10-21 | By bekathwia

License: General Public License 4-20mA Battery Holders Wearables LilyPad

Today I'm making a coin cell battery holder - my first assembled PCB product.‎

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I have been selling purple coin cell battery holders in my LED sewing kit for years. They're ‎perfect for making a simple circuit, and they have a handy on-off switch, so you don't have to ‎take the battery out to power off your project. Before these boards were available, I would use a ‎surface-mount coin cell battery holder with tiny holes in the metal tabs. I had just enough space ‎to sew a few stitches through those holes with conductive thread. They weren’t designed for this ‎purpose and didn't have that handy switch, but they were better than the through-hole variety ‎available since those don't have holes in the tabs at all.‎

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There are a handful of circuits like this on the market that include a coin cell battery clip, a single ‎on/off switch on a PCB, and tabs or holes to connect it to the rest of your circuit, either by ‎soldering to the pad or sewing through the holes with conductive thread. The design I was using ‎in my kit was a knockoff of a SparkFun Lilypad product, an open-source design. I don't feel ‎great about buying the clones, but I was looking for the best price available for my kits. My ‎version observes the open-source license, which means you can download my files too.‎

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To make my own version, I started with that same open-source design for the sewable LilyPad ‎CR2032 coin cell battery holder. I used Autodesk Fusion for this project, partially because it's ‎what I already know how to use, and because the design files are Eagle files, which is the ‎previous name of the software package that was rolled into Fusion. The personal use version of ‎Fusion is free, and it has enough features to do all the things I'm going to do today. ‎

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I imported the files, installed the libraries needed, and made a few adjustments to the design. The ‎first change I made was to have three grounds and one power. This is just so that I can turn the ‎battery connector 90 degrees, and have it face the way I want in my projects. It's just something ‎that annoyed me about the other one, and when designing my own I get to satisfy my personal ‎preference.‎

The second update involved making sure the components available today matched my circuit ‎design. When I was uploading to JLCPCB, the partner for this project, I had to pick out new ‎components that matched the footprints of the components that were spec’d in the original open-‎source design. To do this, I just opened up the data sheets of the specified products and the ‎products available to me through JLC and found ones that had the exact same spacing between ‎their pads. I easily found a battery clip and switch that would fit. ‎

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Also, on JLC, I set the board thickness to be thinner than the average PCB to keep the circuit ‎lightweight and set the board color to black - because black goes with everything. Now, if I want ‎to put the battery on the outside of a project where the electronics are visible, the black is going ‎to match better than purple.‎

Once JLC had my board files and my bill of materials for the parts that go on the board, they ‎went ahead and manufactured them. That involves making a stencil for the solder paste, ‎applying the solder paste with the stencil, populating the board with a pick and place machine, ‎and then running the board through a solder reflow oven. ‎

One of the things that makes this process more efficient is panelizing the boards, which they also ‎did for me, to fill up the full width of the machine with many boards that can be broken apart ‎later. ‎

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My order arrived quickly, which was great because I was excited to check out my first PCB ‎product - hot off the press! I tested the battery holders by holding an LED up to them, putting a ‎battery in, and testing that the switch worked. I also tested these for longevity by leaving a ‎battery in the holder for over a week. I wanted to make sure that the pressure of the battery clip ‎doesn't spring the clip loose. Sometimes that happens with lower-quality clips - the spring loading ‎puts too much pressure on the less-than-high-quality solder joints and the thing pops off. ‎Everything tested perfectly! ‎

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After these tests, I know I can trust these in my kits. So, if you order an LED sewing kit from me ‎from now on you will get my black custom battery holders instead of the purple ones. I’ve also ‎made them available as a two-pack standalone product, in case you just want to get your hands ‎on the battery holders.‎

If you want to get started making your own PCBs, I have a video on the DigiKey channel about ‎getting started making your first board using Fusion. I’m most familiar with Fusion, and the ‎channel already has some great KiCad tutorials from Shawn Hymel too. ‎

So, whether you're just starting out in your PCB design journey, or you just want to add some ‎LEDs to your sewing project, I hope my experience leaves you inspired to create something ‎new.