For mass manufacturing, extra conductive layer can be used between two isolation layers. This is common solution for high-frequency devices which need separate ground, as far as I know such isolator-conduction-isolator sandwich layer can be made with electro-plating technology.
MCU choice, I don’t recall the MCU they used to do it but the t85 is just to power hungry (not really though, it’s quite efficient but in this case it requires more current then the stock driver did). My first version utilized a t13 (obviously with much more basic Fw) and it ran just fine at high pwm rates, it wasn’t till my second version with the t85 I learned of the issue. I had to slow the pwm rate down in code as well as enable the 8x clock divider fuse just to get it to not shut down above medium modes.
Even still, if you go from off to turbo it has problems (but you can start at low/med and ramp up).
The link you posted isn’t exactly what I was thinking… I have some flat flex cables from inside a monitor I converted to LED, they’re high strand count so I was thinking even if they do abrade away with use there’s so many of them you should get a pretty good usable life.
I’ve been thinking about it a bit - CF is indeed conductive and actually enough to be a potential source of problems.
But this is easy to overcome - use some other kind of fibres to reinforce the plastic. Glass / aramid / cellulose / …
There’s a similar thing that could be used - make the driver-tailcap as a single rigid-flex board. That would enable arbitrary number of conductors (non-conductive battery tube, rgb tail indicator etc.). But wouldn’t be really replaceable, woudn’t allow different batt tube lengths and abrasion would still be a problem.
Has anyone ever made a light where the tail switch simply pressed onto the battery and moved it? The battery could then press a switch on the driver board. You might need a plastic carrier to protect the battery wrap.
Here I copied over the idea I presented in tterev3’s post… I feel like this is viable solution that could start conversation.
I have had ideas though. They would work I believe, but trade off those few mm of diameter for a special cell design (like the Fenix did with the LC40) with + and - contacts in the front, along with a “-” at the rear in the normal position. The driver would be designed to take main drive current through the front two concentric contacts, bypassing the tube altogether. The tube can be isolated from the main power delivery circuit, and re purposed as a switching signal.
One more twist on 18650s / UF10….
Put the driver at the tail.
Then make a smart tailcap board and put it on the front.
Now the light can have:
RGB aux LEDs with voltage indication
thermal protection
Thermal protection … interferes with modes of the actual driver. It’s no easy to do it well. One could envision the front driver communicating temperature to the tail driver by manipulating the current that passes through the circuit somehow. It’s not easy.
Or it could just regulate by itself, leaving the tail driver at whatever mode it had. It’s very ugly and inefficient.
With both drivers being constant-current they could actually negotiate with one hard-clamping current and the other noticing that.
But it’s simple to make thermal protection good enough to be viable - just treat it as a protection feature and do a hard shutdown upon severe overheating.
Driver-in-tail designs (eg, Luxpro 2×D lights, as well as some “better” zoomies) do this. Usual way to distinguish them is a light-touch switch, not the usual angry-clicky types.
The driver-in-tail naturally interrupts the current flow for a very short time, just enough to let power flow into the driver board. Think of it as ~99% PWM maximum. Big honkin’ FET does the interrupting. Also PWMs the current to the LED accordingly.