THE DAY AFTER......
As we walk casually to the workshop, and discuss the various quad copter projects, and my old Traxxas RC truck which I have up the bench to repair it's glow engine and trying to find other radioactive sources to test geiger counters and build RNGs
Probably radioactive las vegas dust
Our attention turns to what we're going to do next with the board, we've been talking to the good folks at crowdsupply as well. So we talk about adding all the features you'd want to see in a board that isn't meant for a 3 day hacking conference.
Adding TMOVs, input protection,SWCAN, LIN, optical and galvanic isolation to USB, talking about USB 3.1, then we looked at a chip upgrade which for some reason i'd convinced myself STMicro had made a 2Ghz STM32, in my defence i'd been spending all week working on Snapdragons for Quads and stuff. We ended up deciding to move up to an even moar powerful chip for the after con board.
Then we played around a bit with a HIL Drone Project in VR with the Vive that i've been playing around with, fun stuff... So far pretty chilled and not too much worry about the board, we even took one of the fried boards from a few weeks ago and changed out the CPU, and removed the power section so even that was fixed up, so far so good.... We turned to sourcing parts and taking about the various battery tests and how one of the battery that claims to be 2x the mAh is half the weight of a decent 18650.
So we start fiddling around with the solution we though we had settled on, an external 18650 case that has USB in and and out, and boosts it to 5V and charges it, I bought a bunch of them from eBay etc to test with as usual.
So far so good.....dun dun duuuuuaaaa
Then I pull out the PCB's I'd ordered with the USB boost on them, and that is when it all goes the usual way, We test a lot, we test all sorts of batteries, charger circuits,. design and redesign but we had a hard time making a circuit that could charge an 18650 and supply 5V, which is why we'd decided to drop out nice TI boost, charger, fuel monitor, auto power switch version which had a large cost and component count, and just use these little self contained power cells, a USB cable to plug into the board and hang it off the badge,. cost is a big factor, and we always end up over budget.
Pictured above are a range of 18650s , the rule is the higher the claimed mAh is , the lower mAh it actually is. the 6000mAh we reckon to be about 1800mAh give or take. We're pulling some of these in for sub $1 and with a draw of about 50mA for the badge.
The ones in the mylar bags are just an eBay lot of the power pack chargers, the one on the right in the blue box is what we were thinking...
Personally we hate it, its a terrible design choice, but it was a struggle to get it on board and be reasonable, and its hard to beat these boards for cost. I don't like using modules to build badges, I get why, it makes sense but I don't have to like it.
So then we start to poke around the boards a bit and see what they're upto, the first one has a bunch of stuff, charger/boost chip, battery monitor, FETs and a lot of components, one has three chips and 6 jellybeans, then we get to one that has about 5 components, a quick RE of the board and its feeding the VUSB via a resistor, a diode to drop the voltage 0.7V into the battery, then a booster and out to the USB with a couple of LEDs, it is an unmarked IC but some searching around we find it.
So far these are the chips commonly found in these powerbank setups
DW01 One Cell Lithium-ion/Polymer Battery Protection IC
High Efficiency 1MHz, 2A Step Up Regulator
Single Lithium Cell Protection IC
Usually a CD43 sized 1.5uH power inductor,. though I see 2.2uH in most datasheets it might be a part on hand thing since thats usually the availability step, 1.5uH and next 2.2uH
A couple of caps, one in , one out, two resistors and an LED.
I find these guys too Battery Charger as usual...
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