Remote switch tail board with FET, so no added resistance

Annoyed with the low output with remote pressure switches for flashlight?

I did a board with a MOSFET to eliminate the extra resistance from the external switch
size 16-17mm, for 16mm the battery holder fins need to be cut a bit

I use a MOSFET with a low gate voltage which gets full output down to 1.8V

The MOSFET is powered by a CR1225 Lithium battery with 36mAh should run easily hundreds of hours on

Aliexpress has cheap remote switches, you could dismantle for the cable and pressure switch, or one that fits your flashlight

Please forgive me as ask . What is fet ?? # newbie question

Very Interesting, :beer: And if you do a copper bypass on the spring, by how much do you think it can reduce the resistance? Maybe something to incorporate to the illuminated switches…

Good job!

If you do a run I’d be interested in a couple of these :heart_eyes:

for FET read this

The intention for this is not to replace a normal tail switch, but external switches
with a spring bypass this will be the same as with a normal tail switch, so you can run your 3000 lumens light with a remote pressure switch without smoking the switch

the external remote switch becomes basically just an e-switch, with the FET replacing the tail switch

I always wondered why nobody had done this, but didn’t really have a reason to myself. Nice work.

Can you make a part list for this? I mean what resistor valuse and diode and an example fet type. And then I will build some for me. Can you eliminate the button battery with a bleeder resistor or it doesn’t work without it anyway?

You can use a 4.2V supercapacitor, or 3.3V supercap with 3.3V LDO or a 3.7V rechargeable button cell with bleeder

But the 20 cent button cell should last for several 100 hours you push the button, and it is as expensive as the shottky diode

I will make it open source when I have tested it

The first 9 boards I ordered had a error rendering em useless

Thank you!


If you used a PFET you wouldn’t need any gate supply at-all.

And a couple of nand gates could give you a toggling on-off switch, it might need e.g. a cap. and maybe a little bleed resistor to hold up supply to the toggle, or not.

I think someone on CPF used to make these, with NFET and cell, a while ago.

But for e.g a gun torch, just direct drive through a FET in the tailcap works so well. Whether triggered by a button, or remote switch.

You mean a P-FET should work just connecting ground to it, this one needs a bleeder probably on the main driver
just unsure if this one would need a gate resistor to positive side, which would let the main LED glow very low
I have searched for a suitable source and I think I found a few with lower resistance and working voltage down to 2V

I just wan’t ready plug and play versions of this :slight_smile:

The gate resistor is necessary to keep the thing switched off, but it passes no current when off. It is just there to ensure the gate is discharged, any tiny leakage might mess things up. No power consumed. No LED glow.

It does work. There are good PFETS around these days, this is a standard arrangement for reverse protection or totally removing power (ignition switch) in automotive applications, and there are some great devices.

NFETs are what youngsters are trained about, and the modern logic-level ones are so impressive, compared with e.g the first IR HexFets that I helped design over 30 years ago. But PFETs have developed too, and are fit for purpose in this sort of thing. On and off. Maybe not fast PWM.

We used to worry about mobility of holes vs. electrons, but that is less of a problem these days (but electrons still move much better) :wink: .

I looked at good P-FETs and I found one Vishay, the thing is it costs more than the battery with holder for the N channel, also the battery increase the overall thickness of the board so it is more compatible to regular switch boards with the switch taking a few mm extra space

I have ordered 3 remote switches
9 boards
not ordered the Mouser parts yet
if there is demand here to buy this board please respond if you want it with switch or just the board assembly

1. luminarium iaculator

  • one board?
    or all parts to mod your tail cap?
    size 17 or 16mm?

Cool! I have no use for this. But still cool! I’m subscribing to see where this one goes! :partying_face:

Well I can’t remember where I posted it years ago but I made my own FET remote switch with some air wiring and random parts I had laying around. Currently on my 12-gauge pump switching an XHP50 in a C8 fed from a couple 18350s. I’ve been meaning to teach myself Eagle so I could design a neater solution, but I haven’t. So I’ll be in for a few if these turn out well. I’m actually really interested in a PFET version if it saves space as the 2S 18350s are a bit of a squeeze. Plus I’m considering boring a C8 tube to take a 21700 and need the length there too. Additionally, I’d feel more comfortable not relying on the coin cell connections in a high recoil application. Though my hack job homemade setup has done surprisingly well…

Hi :slight_smile:

Sure put me in a list for one with cable… If I will like it I will order more.

I thought that 20mm boards are more standard ones? 90% of Uniquefire flashlights, Brinyte, Mitkos Supwildfires etc….

Let the reference of Omten or Kan 28 switch guides you… Flashlight who has them installed must have at least 20 mm switch board because their size is 18mm(cube) and 19-19,5 at contacts below.

But of course I am still in cause it is no problem for me to piggy back it to 20mm board :slight_smile:

Yes… Contacts must be solid and I think it wont be problems.

How to simulate recoil? Take flashlight in one hand while holding pressure switch turned on with other hand and then take your best and hardest twitch with a hand like you’r gonna throw it to floor. Do several of “simulating throws” in a row and if flashlight will not loose a contact you have good setup.

Edit: It should not change modes either…

:beer: :beer: :beer:

I wanted to build this for a long time (but lack of electronic knowledge stopped me doing that).