So, I have this idea to build a nice weapon light for my rifle. I’m going to use a convoy c8 as the host and a DD driver with a dedomed xp-g2. I want to use one of those remote mount momentary switches, bit the wires are tiny and probably not good for carrying current. I want to make a custom pcb with a MOSFET as the main switch and the remote switch as the gate switch. Has anyone ever tried this or anything similar?
You need to power the MOSFET with either a separate power supply or run another wire from the head of the flashlight.
What if I had a resistor to bypass the capacitor on the driver, similar to the way the lighted tail cap operates. Would that allow enough power to bypass the driver and power the mosfet? I’m gonna see about getting some parts and see what I can rig up.
That path only provides power when the main led is off.
You can use a lithium coin cell to power the mosfet.
Honestly, my last 5-pack of TianQiu CR2032’s just cost me $0’99 CAD. The next-to-last was free because it arrived home well after the seller reimbursed me the money, and she even reimbursed me back my €0’70 donative after explaining her the Christmas package had arrived. OMG LOL! :person_facepalming:
Cheers :partying_face:
The capacitor idea sounds good. I just know I want to avoid adding extra batteries if I can. I only need momentary operation and I really want to keep everything on a 17mm pcb if I can.
I just don’t know how much voltage you do need but, truckloads of LR44s are cheeeap. LOL! :money_mouth_face:
Cheers :partying_face:
A FET Tailswitch would be a God-send for high powered non e-switch lights.
Do I smell another revision of the lighted tail-cap in the oven??
Maybe… would be nice to see an eswitch tail!
What is the diameter of the convoy c8 tail switch board?
It measures 16mm, but a 17mm board will fit
How much vertical room is there to work with?
Many people who would use it? I mean, I do see the need but I would have thought that if a lot of people want it, someone would have made an oshpark board by now.
Just out of interest, is the light only to stay on for as long as the remote switch is pressed, or should it latch?
Not that I can help with the design, just curious as I could put this to use for something else.
For my uses I just need momentary operation only. So the light should only be on when the switch is pressed. Kind of like a half press of a clicky switch.
I’ll check on the vertical space as soon as I get home. I think there should be a good 8mm or better because of the height of the original clicky switch.
I’ve actually made one by hand already… I’m running an XHP50 direct drive off two Efest 18350’s in a convoy C8. I forget exactly the combination of parts I used, but I’m pretty sure it was the momentary C8 tailcap from MTN that I stole the tape switch and coiled wire from and transplanted into the stock C8 tailcap. I’ll have to check when I get home, but I did this since the stock tailcap was longer than the momentary one. I used a 70N02, 2032 coin cell, some random hundreds of kilo-ohm (metal-film?) resistor that I robbed from an old DMM board, a copper washer, some 24awg wire, full copper faced FR4, and some hot glue, a file, and patience. The light is mounted on the end of my shotgun via some modified Gearbest weapon mounts (very stable now, and $6 invested). I check up on it every few days to check it and gain confidence in it’s functionality. It has been pretty reliable so far…
To fit in the tail it would need to be small cell. Tru3s1lv3r said the switch board is 16mm, I presume it rests on a ledge and the cavity is less than 16mm. The options I see are CR1025 30mAh CR1220 35mAh, BR1225 48mAh (all panasonic numbers). At 3uA it should take 10,000 hours to drain 30mAh. Haven’t looked into what point the voltage would drop too low. So maybe cut it in half, that’s 208 days. Have I made any mistake here? 
Puts a damper on the idea for me. At least for lights that can’t accommodate a larger coin cell. And with a smaller cell I would want to use battery holder for easier replacement, instead of just soldered. So that takes a bit of space too.
Have you posted pictures anywhere? I know I’ve seen one before. Maybe it was yours.
Panasonic says their CR2032 provides 225mAh. Much better.
+1 on the pics. If it’s a WML I think I’ve seen it mentioned as well but never saw pics…
For me, the potential reduction in resistance, & not having to replace a worn out switch, sounds like a winner, particularly in high-Amp lights.
I had pondered the idea of a FET switch before, but had not thought of the simple solution of using a button cell to switch the FET.
Like the lighted tail switch, I'm sure people will adopt it if made readily available.
It's going to take the right someone/s who have the need & skill-set to come up with a parts list & working OSH Park board, & I hope this is the start of it :)
That’s awesome, JaredM. I’m sure plenty of people are interested in the details of what you have done. 
Ah, yes. :weary: Might help actually being awake.