2019 Burning Man Pendant

#For wearable projects 18650 lithium cells tend to be too large. I see tons of project using flat lithium packs instead or just non-rechargeable alkaline batteries. I don't like flat pack lithium batteries since they are easy to puncture and with a hard case they are almost as large as 18650s. 

There is a good alternative which is a good compromise between size, sturdiness and capacity: The cylindrical 14500 lithium battery. 14500 is essentially the same size as an AA alkaline battery. From what I can gather there is pretty much only one company which sells them in quantities in the US: Tenergy. These batteries have a 800mAh capacity which is pretty good for their size and they are fairly sturdy while being small enough. I buy them in batches of 100, at $3.69 a pop. Also, when you order 100 you get them in their original neat packaging. Product page: http://www.tenergy.com/30001 Tenergy has an online store where you can buy direct:  https://power.tenergy.com/tenergy-li-ion-14500-cylindrical-3-7v-800mah-flat-top-rechargeable-battery-ul-listed/ They are based in Fremont, CA. Reputable company from what I can gather, never had an issue with them.

Highly recommended for portable projects where 18650s are just too large.

Before we start on a project which needs a lot of parts we need to make sure we can acquire them. So, I bought all my LEDs before even starting to design the PCB.

Like last year I wanted to go with APA102-2020s since they survive pretty much everything you throw at them. To give you some context, I commonly deal with WS2812/SK6812 modules for other projects and in my experience these modules have a huge downside: The bonding wires inside these don't survive being reflowed twice which is a no-go for a double sided PCB. The APA102-2020 module on the other hand is completely epoxied in, without loose bond wires. But they have a huge downside too: They are a PITA to reflow properly without bridging. The pads on the bottom are just too damn small:

But we have a new contender on the block, the WS2812C-2020. Like the APA102-2020 they are completely epoxied in and survive several reflows easily and more importantly they are super easy to even solder by hand, despite their small 2mm x 2mm size.

So where to get them? Pretty much the only choice is AliExpress. When you search for 'WS2812C-2020' you get a bunch of vendors, but most of them only sell in hundreds. What I needed were full reels. The best way I found is to contact the seller and ask for a full reel and price quote. A full reel has 4500 modules, I got two for $313.93 each to the door shipped with DHL. Quite affordable at 7cents for each LED module IMO. Now, there is a certain risk with these vendors: last year someone cut open my package (probably deliberately) in transit and I lost a full reel of APA102-2020s... No recourse, no matter how hard I tried since they "correctly" claimed the package arrived at my place. There was just nothing in it anymore. Anyway, I have the reels in my hands: