Noname LED bike helmet autopsy (WHL #81)

Chinese junk that appeared on my work bench this week!

Well – it’s a bike helmet. An LED bike helmet. A colleague brought it over and asked if I could install an USB type-C port since he (or his wife?) brutally murdered the micro USB in the back. Sure, pinouts are basically identical and access to the thing is darn easy. Oh, no, they’re not.

Turns out this thing can be tossed, since he doesn’t want her to use a nonfunctional LED helmet that furthermore still has a ticking lithium time bomb in it. So I did, after extracting all the goodness shown below.

First of all: I don’t know where he bought it, how much he paid, and if that thing is from a reputable manufacturer. I cannot spot any branding and my searches online only revealed a “ROCKBROS” unit that looks very similar, but indeed has some branding on the side. Amazon ships one from “Auvstar” – so this might be a noname unit that everyone can personalize when ordering a 40ft container of it. It costs 60€, which is pretty cheap for LED helmets and significantly more expensive than a regular name-branded unit, so that sounds about right. This is one of their pretty marketing images:

Anyway, here’s the guts in no particular order.
The user interface looks like this and hides three screws. I ripped them out before realizing, but the decal cannot be reattached, so once you’ve removed the top assembly, it’s gone regardless of the opening method. Might still work for a while, but it’s no longer protected against water ingress, and the Rockbros even advertise the “can be operated under water” feature (chances are you’re doing it wrong when biking in such deep waters your helmet starts floating)

This is the middle part of the mounting box for the electronics:

And this is the bottom part. As evident from the tabs all around, this is securely anchored in the styrofoam EPS material and will not come out without thoroughly damaging the unit. I wouldn’t actually trust this helmet after removal, as it might be prone to breaking right there. It might also be one with everything still in place, but you still have the LiPo cell cushioning your impact 🙈

That’s the opposite side for reference, so the EPS has clearly been foamed up after mounting the electronics to fully encapsulate the thing. More on that in a bit.

As for the battery that can be extracted beneath the PCB: Yes, it has its own protection circuit, that’s a big thumbs up, this should be valuable when damaging the charging connector and/or the PCB. Thumbs down for capacity, despite the nice figure of 6.66Wh: The Amazon product advertises 2000mAh capacity, and you wouldn’t know you’re getting scammed since you can not access this thing without breaking everything else. Besides, I did not test it (looks alright to me though, takes 1A of charging current at 3.9V no-load voltage), but it might be even lower than the figure they printed onto it.

What else have we got…yes, the USB board. It’s mounted to the front, so in theory knowing this all beforehand, one *could* extract the module from the EPS foam and then insert like a barrel connector instead. Terrible look, but would save it from being scrapped prematurely. But this is clearly not intended to be serviced (check the helmet imprint above to see how much I needed to dig down to extract this), and that is, especially for such a fragile and exposed connector, a huge construction fail.

And here’s a bunch of labelling, about the only stickers that I found on the entire helmet.

In terms of electronics, there’s six LEDs on the back side of the helmet (mixed with the button interface) and three more (red-blue-red) on each side. As far as I know blue lights on any car are illegal in Germany, those are reserved for like police and ambulance. Blinking lights are illegal as well, and those LEDs might be blinking. But so is the front white light in mode 3, and many biking idiots actually use them. So there’s that. The side LEDs are actually somewhat serviceable since they’re not embedded that deeply and can be popped out with a screwdriver. So if the double-illegal blue blinking light fails, this might be repairable. Fat bikers can also switch over to yellow lights, although I think that is mandatory at a certain length, not tonnage

LEDs are in parallel with different resistors (680R and “none, just the wire resistance”) to account for the different threshold voltages.

Could easily be glued back in, don’t you think?

As for the more important light at the front, this LED can be adjusted in angle a bit (not much, but a bit). Judging by the lens, I’d say the LED chip is clearly visible as projection, so the cold white light is confined to a square and doesn’t flood all that well.

Surprisingly, the case is actually metal, this is not only a good idea for the anchoring pin, but also for heat sinking purposes.

Disassembly yield the following items: A cheap and already pretty scratched-up plastic lens, the shell and front ring made from black anodized aluminium, an inner retaining ring that was pretty loose, corroded and only has like 2.5 full threads, and the LED assembly with a partially anodized housing.

Heat sinking: Possible in theory, botched in real life. A small dab on the other half could have done so much. At one Watt, it’s easy to hold the LED in your hands, it just gets a little warm but that’s about it. If they drive the thing harder, and it is entirely possible they do – at 4.15V it peaks at 3.5A, that’s what my power supply can do. That’s almost 15W in case they simply route it through and the only limiting resistor is the very thin copper wire.

In reality it’s somewhere in the middle, although I cannot tell for sure – of course they fucking rubbed off the markings of the large chip, with the 8-pin one being a “4056 GC2026”, pin-matching the TP4056 1A Li-Ion charging chip, and the small 6-pin being a “7136 2012”, which might actually be a SOT-89-5 with tab, an adjustable 1A constant current driver found as QX7136, HT7136 or MEL7136. So if they use it to full capacity, that’ll be 1.0A at 3.15V or 3.15W – it’s getting hot preeetty quickly. The board, if anyone comes here via a Google search, is labelled as “HT16-60C”.

Last, but not least: The spectrum of the white LED. Very cold, clearly lacking yellow and there’s also pretty much nothing in between a strong blue and the green part of the phosphor (spectrum has about a +15nm offset if you care about the exact wave lengths). It’ll do for being seen, it might be not enough to bike in the dark with just that light source, and it certainly has terribly color reproduction, but what do you expect from a bike helmet.

Into the bin, next!

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