James Munns

doing ANOTHER take on "MCU with DC/DC converter and RS-485 transceiver". This is an early draft, figuring out roughly the board outline and how much space I have to work with.

I think for my battery powered stuff, doing a bus actually ends up being less of a benefit than it would be in a static home installation. I'm banking that it's easier to have a single cat5 cable per node, with 3x power pairs (12.8V, capable of about 10-15W) and 1x data pairs, than have to daisy chain a heavier gauge power cable (with ring terminals) as well as something, probably cat5, just for the single data pair.

The SOM in the middle is a "Mini560" DC/DC converter, which is hella cheap, and can do 2-3A output pretty comfortably. For an MCU, this time I might use the lqfp-48 stm32g030 instead of the tssop-20 (which I used in my "amodem" project), since then I can potentially have some more digital I/Os.

It should fit on a 6x8 lego plate, for making a prototype case.

Sometimes super-specific domain knowledge shows up in surprising places. Tubular Li-Ion cells (e.g. 18650s, 20700, 21700) are widely used in a LOT of stuff, from power tool battery packs, to electric cars, flashlights, and specifically: electronic cigarettes.

Electronic cigarettes are an interesting application, because they require a LOT of current, typically 10-75W or so, which can be as much as 20 Amps of current in short bursts. They also need to have a relatively high capacity (so you aren't charging it all of the time), as well as be relatively safe (it's near your face).

Before e-cigs, the only application you'd typically buy 18650 cells as a consumer was for high powered flashlights (fun fact, a lot of e-cig history actually derives from high power flashlights, the reason e-cigs are typically called "mods", is that they were originally "modifications" of high power flashlight bodies).

As flashlights were a relatively small and niche market, there weren't a lot of objective "ratings" for cells, which could generally be WAY overstated, especially from shady (read: eBay and AliExpress) vendors. When e-cigs started using these overrated batteries, it could range from disappointing to dangerous.

One of the coolest resources nowadays is from a guy named Mooch315, who is an electrical engineer who does lab-style testing on batteries. He posts his findings, and is pretty much the ONLY source I trust when choosing Lithium Ion batteries, for e-cig purposes or other electronics usages. He even tracks how popular cells are cloned (with substandard replacements), and how to spot fakes.

Here's a link to his forum post, which he regularly updates with recommendations:

I ended up finishing the second battery test, which only came in at 14Ah out of the rated 24Ah. To their credit, VHBW gave me a refund. To their not credit, in my sample size of two, both batteries were generally only 60% of their rated capacity. I ordered one of these as a replacement:

I've heard good things about Renogy, so we'll see how it goes. The dream of holding an outdoor stammtisch here in Berlin lives and waits for another day.

One "dream gig" idea I have is to pick a certain piece of embedded hardware, something with some complex bits, maybe like the pinetime, or the wio terminal, or maybe even something bigger like the uconsole, and spend a year focused on it, while doing regular teaching guides on electronics and embedded rust on it.

Basically, just a super-annotated development process, with people following along to learn electronics, software, embedded, rust, etc.

That being said: I have no idea how to sustainably market this. The people that would benefit most from this (students, people changing careers) have the least to spend. Some hardware companies might be interested - but they usually draw the line at some free hardware, or a discount code for a course.

Just a crazy Friday idea for you.