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A project log for Thunder pack

An ARM board with built-in battery, charger and high power outputs that fits in your pocket.

JeremyJeremy 09/20/2019 at 17:410 Comments

This is one of those projects that I've been casually working on for the past couple years. Every few months I pick it up, iterate on it a bit, and then put it away. Well, the past few months have seen a great deal of progress and I'm really happy with how far it's come. 

In fact, I took one of the recent iterations of it to Burning Man and it survived the week in the harsh elements beautifully. Nothing beats some real-world testing.

Here's a brief rundown on what's been changing:

More Power

I've upgraded the MOSFETS to supply max 2.3A per PWM channel (there are 4 PWM channels!!! You know, so you can drive really big LEDs or just a long string of them. (however, you're still limited by the battery voltage)

The lithium battery charger IC has been changed to more than double the charging current from 500mA to 1.1A.

So Many Example Programs

II've been going crazy writing examples for the board across 4 different popular HAL libraries:

My goal is to have the same examples for each HAL (with some exceptions) so people can compare 1:1 how the libraries differ. It could even be a useful tool for people looking to switch from one library to another (maybe someone familiar with Arduino wants to get closer to the bare metal).

PCB: 2-Layer -> 4-Layer -> 2-Layer

Even though the overall circuit design isn't too complicated, it can be challenging to effectively route everything on such a narrow board. After reading Hackaday's article on 4-layer PCBs, I decided to give 4 layers a try. It truly made routing the PCB so much easier! 

The only problem, though, is the cost. It's still twice as expensive as a 2 layer board, and even more with some PCB houses. For a prototype run, it averages out to $8+/board just for the PCB. Because I want this board to be economical and accessible to anyone, I've decided to switch back to the 2-layer design (although, I could be convinced to keep 4-layers).

The latest 2-layer redesign feels fine, however, I'm still a long way from from being a PCB designing expert. So if anyone is interested in taking a look at the latest iteration, I'd love feedback: 

https://github.com/jgillick/ThunderPack/tree/527309ebf9d86e02591bb936e8c22aa9c7aaf138/hardware/STM32L0xx

Name Change

I was never really happy with calling the project "Lit Fist". It seemed to pigeonhole it as purely an LED controller. Even though that was the original goal of this project, it has been expanded to be much more than that. Now I see it as a general purpose battery-powered, ARM board with 4 high current outputs and 10 GPIOs. With that in mind, the name has been changed to "Thunder Pack". It still makes for a pretty awesome personal LED controller for wearable projects.

What's Next?

This morning I submitted an order for a fresh run of prototype boards with the new 2-layer design. Now comes the part that I hate...waiting for the PCBs (it's like waiting for Christmas as a kid). When they arrive and if they work as expected, we'll be at a place to call this project feature complete! Until then, I'll keep myself busy writing documentation and coming up with more examples. Stay tuned.

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