2019 Burning Man Pendant

Wearable LED lights with built-in communication

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This is the 3rd iteration of this project. The basic idea is is to provide customizable and rechargeable LED lights to everyone in our Burning Man camp.

The basic requirements are:

- I need to make 60 of them.
- Has to last an entire night without recharging.
- Use rechargeable battery vs throwaway cells.
- The pendant is double sided, i.e. you do not need make sure that it's right side up.
- Customizable. This means the ability to customize colors and offer enough modes so pendant do not look alike when they are running.
- Somewhat sturdy.

Last years revision added the capability to broadcast 8 character messages to everyone. It uses a LoRa radio chip to do so. The plan to extend the software to use ranging this year.

This years version uses the following components:

- Main PCB is 58mm x 58mm
- A Tenergy 3.7V 800mAh Lithium-Ion 14500 battery (essentially a AA sized lithium cell)
- The fairly new WS2812C-2020 LED module, which is the 5mA variant. There are 66 of these per pendant.
- An ATSAMD51G18A which is a Cortex-4MF MCU with 256KB of flash memory.
- A Ti BQ25895 as the PMIC for the LiPo battery. 
- A SX1280 radio chip for communication.
- A I2C 0.69 inch 96x16 OLED b/w display (ER-OLED0.69-1W)
- Two FETs to turn the LEDs on and off
- A off branch 3.3V LDO regulator
- 1x main switch
- 3x tactile buttons
- Lots of passives, all 0603 parts
- M2 nylon bolts, nuts and washers as spacers
- Laser cut acrylic cover/diffuser.
- A 2.4Ghz tuned WiFi antenna.

  • 66 × Worldsemi WS2020C-2020 LED module
  • 1 × Atmel ATSAMD51G18A Microprocessors, Microcontrollers, DSPs / Microcontrollers (MCUs)
  • 3 × Hongyuan Precision 1TS002B-2500-4300-CT Tactile Switch
  • 1 × Korean Hroparts Elec K3-2235S-K1 Toggle Switch
  • 1 × Texas Instruments BQ25895RTWR PMIC

View all 16 components

  • The 18650 alternative: 14500

    Tinic Uro05/17/2019 at 19:26 0 comments

    #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: Tenergy has an online store where you can buy direct: 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.

  • Aquiring 9000 LED modules

    Tinic Uro05/17/2019 at 19:06 0 comments

    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:

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Mike Szczys wrote 06/04/2019 at 16:21 point

Using that 14500 cell is a neat tip. But I'm having trouble grasping the scale of that cell versus the badge itself. Do you have any images with the cell installed in the badge?

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Michael G wrote 05/25/2019 at 06:26 point

Any way to  make the PCB fit entirely behind the diffuser? Not sure if that's what you're going for though

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