Until a few get built its probably going to be a DIY board and parts list at best. At that point maybe someone can enlist Simon at Convoy to see about an oem replacement tail cap. For now you can probably just scavenge a switch board and air wire the fet, cell tabs, and switch wires. You’d have to do that with a driver anyway.
I’d be extremely interested in an oshpark board. Excited.
[quote=Sharpie]
I’m getting a bit lost here. Are you saying that when in use, should the cell/cap drop below threshold power the light would go off?
So if one tests the light for function momentarily, would that charge the cap? Just trying to get my head wrapped around this after a long intense day at work 
Phil
R.E. lighted tail cap: Anything located in the tail cap is located after the led in the circuit so there isn’t any voltage left to power it when the light is on. With the light off a trickle of current flows through the leak resistor but the main voltage drop occurs across the led(s) in the tail. Led’s, mcu, or gate of an fet there is only voltage available when the light is off unless another source like a cell or super cap is added. A light with a cell carrier might be modded to bring voltage to the tail cap but that means either a bigger light or low capacity cells(3 X 10440).
Only mentioned the lighted tail cap to illustrate the voltage issue. I suggested a rechargeable cell because of its higher voltage and the solder tabs which eliminate the need for a holder which would occupy space and need to be accessible. In any case, I’m just contributing suggestions not pushing for any particular design.
In post #34, Sharpie lays it out pretty clearly what to do for a momentary setup.
I’m more interested in what’s needed to make a latching circuit(if that’s the right term).
Ie; replace the clicky switch inside the tailcap with small e-switch, & the CAP/coin cell FET circuit described above, but have the FET switched & held by each ‘click’ of the e-switch.
What would need to be added to that circuit, or changed, for this to happen?
My guess for this to happen would to build a flip flop circuit. It would add more components, but I think that will work for that application.
I’m seeing both sides of this coin here. Replacing a mechanical PB with an electronic one controlling a FET will be awesome for radical amps; and from looking at the amazing Lighted Tailcap “project” it appears there’s plenty of room for a flip-flop. (BTW, in case anyone’s interested, old computer keyboards are an excellent source of tiny momentary switches…)
OTOH, I’ve had a rifle light mounted since before Cree made LEDs; in which the remote switch would become a fusible link if I tried it on even an entry-level C8…
An extra battery bothers me, though. I’d like to put in a vote for the capacitor, since I would never use a rifle light for general illumination & almost never leave it on for more than a few seconds.
If the driver can provide the power and a small cap can keep the FET turned on for, say 15 seconds or so, that would be pretty awesome, in my world.
(Posting this just to subscribe. Back to lurking…)
EDIT: with this foundation, you could replace the switch with one of those “touch-switch” circuits. Then to turn on the torch, just pick it up! Oooooo!
Thanks, Sharpie.
I’m pretty keen to get one of these happening. 
I was thinking there are a lot of ways a pressure switch can get pressed accidentally…
And if you’re making enough light to be useful, you’d be making enough heat to be dangerous. In the case, across your shoulder in daylight, etc. Sometimes we might forget to unscrew the tailcap…
It seems to me, a for a targeting light, straight DD with a recoil-proof spring & braid at B+ to the LED, then a MOSFET tailcap Gated by the pressure switch, would be a great combination, and if you sized your supercap to discharge w/in a half-minute or less (maybe even a lot less, for safety and a much smaller cap), wouldn’t that be useful, at a minimum complexity level & BOM? Obviously with no driver to leak current, you’d need a wee bleeder resistor to charge the supercap.
I went looking for a MOSFET. Has anyone ever heard of or tried one of these 360μΩ, 5 V/60 A N-Channel MOSFET ? It’s spendy, but for a single-cell light (max VDSS is only 5V) the 60A limit looks intriguing, and it supposedly turns on in 1.2V so it doesn’t eat much.
It’s cute as a button & would leave lots of room for other goodies.
I’d appreciate some opinions, since this almost seems “too good to be true”…
Am I off base here, or does that seem like a useful MOSFET (if priced somewhat ‘regally’…)?
Wow, looks like it’s fully on above ~1.5V, that’s pretty amazing.
Danger, Will Robinson
Can I get a sanity check, please? I think this answers the OP question. If I had any artistic skill at all, I promise I would use it.
Thinking about a targeting light, this is essentially (and crudely, go ahead, I know) what I would try (and will, if this seems workable) to get Momentary-ON, DD, brutally simple, and small enough to fit in a stock C8 tailcap:
(Click the pic for a nifty drawing tool, courtesy of DigiKey!)
I understand that this is a 1st-order approximation, and that it will probably kill anyone who looks at it, with the 18650 and all. Seriously, I wonder if the XM-L’s limits wouldn’t protect the battery, if it stops conducting at ~3v or so… But the only protection here is You. Don’t try this at home!
Mechanically, the battery would be cushioned by heavy springs & O-rings or foam washers. The connections would all be with solder braid except the line at the bottom represents the C8 body and the circuit of R1 & S1 to Q1 Gate wouldn’t need much of a wire. The MOSFET would be the one linked above, the LED would be a nicely-colored XM-L(2) (to keep everything “Budget”), the Momentary Switch at the Left would be the pressure-switch mounted in a convenient spot on the rifle. I’m not sure that R1 needs any specific value, but higher would seem better. Apparently all you’d need is 1.5VGS.
Or did I pick the wrong day to quit sniffing glue?
Thanks to any for any feedback. I already have the gun mount installed, the rings for the body, and the remote switch… Oh, and a new C8 host.
(please use whatever words you deem appropriate)
EDIT: BTW, this works in the sim, but that doesn’t mean it would work IRL.
Sorry to bump this one out of the grave, but I’d really appreciate some feedback. Does my simple sketch seem feasible for the OP?
Full disclosure, I’ve built a new C8 & bought a matching one from Convoy. I planned on doing a pro-DIY thread, but since I don’t have the measuring tools other than for tailcap current & my eyeballs, other than the anodizing color I can’t tell enough performance difference to be worth the $2 price difference. Ergo, my new DIY body gets to become what the OP wanted.
That was very similar to the original idea had. Just a single MOSFET on a board to fit in the tail cap. It works in circuit simulators, but I haven’t had the time to get all the parts in and actually do a physical test with them. I guess I’m just gonna have to bite the bullet and take a day off work or something!
I love this idea! No more worrying about those horrible current robbing switches.
Thanks, Sharpie. I actually did think about it, quite a lot; and worked it out on the Sim to the minimum BOM I could get to work — on the Sim…
And then burned out my last bran cell when I picked the wrong stinking symbol on DigiKey’s drawing app!!! :person_facepalming: 
If you hadn’t mentioned nFETs and pFETs I might still not see it. I appreciate the heads-up!
The nFET I thought I was using is a Vicor PI5101-01-LGIZ … 5V, 60A w/ a .4-.8v VGS (th), I couldn’t resist…
I think (yeah, right) I’m going to go back over it a few more times to see if I made any other errors…
PS: If you give me a perfect straight-edge, a sharp pencil and a few hours, I might draw you a small straight line, if the paper holds out. If the circuit can be made to work, I hope to build it with pixtures…
So… Has this still yet to be done or has someone come up with a working high current remote switched design?
Steve Ku of Veleno designs built a tailcap switch module like this 5+ years ago. He sold them together which a titanium switch button with trit slot and retaining ring for the Sunwayman V10.
I bought a few of the internal switch modules from him at the time, with the intent of modding one into the tailcap of a Sipik 58. Recently, I retrofitted one of the leftover switch modules into my Sunwayman V11R. It works perfectly, but the light only outputs 500 lumens. Not sure it would work well at higher currents.
If you make one and sell it through Mountain Electronics, I’ll buy it! :heart_eyes:
Maybe the attiny version of the lighted tailcap board could be used somehow?