^ mind that a lighted tail the way it is done in this thread only works on li-ion cells because there is no voltage boosting for the tail leds going on. You might get away with a 2xAA light and red tail leds.
Hello all,
Here's my take on the lighted tailcap - a simple version (no microcontroller required!) which has two groups of LEDs and two configurable threshold voltages, for example 3V and 2.7V.
When the voltage is above the first threshold, the primary colour lights up (e.g. Blue). When the voltage is between these two voltages, the 2nd bank of LED is switched on and the first switched off (e.g. Red) - this can act as an indicator to recharge your battery! When the voltage falls below the 2nd threshold, both LED banks shut off to increase standby duration.
Also while at it, why not convert your switch to a FET switch instead?
You can achieve single milliohm switch resistances depending on the FET used. 
The FET board has an onboard tiny rechargeable battery, so servicing is not required once installed! This may be useful for those wanting to increase the durability of the tail switch, esp. on lights with high battery currents.
Please feel free to check out this thread for more information, including OSHpark projects so you can make your own:
https://budgetlightforum.com/t/-/50404
Hopefully this is useful for some people! I know I'll be using it in my lights.
Thanks djozz, I’d forgotten about the voltage issue. :person_facepalming:
I suppose I could use a 14500, but want to avoid letting the kids use Li-Ion cells unsupervised.
A 3xAAA light should work. I put a lighted tailcap in a Sofirn SF30A last night, but it’s a little bit bigger and a lot brighter than I’m hoping for.
Thanks for sharing your designs loneoceans! :+1:
Building them is beyond my capabilities at the moment, but as soon as my skills are up to scratch I want to put them on all my lights. 
This is clever :+1:
Is yellow doomed for being inefficient (ie. high current)? I’ve tried 2 suppliers with similar results, and expecting another supply of 0805 yellow LEDs any day now.
Here are the milliamps for my various tailcaps. The brightness of each is about the same, per the perception of me and my family. If one was considered brighter/dimmer, I would change the resistor value accordingly.
- Orange (.56), yellow (.99), green (.07), blue (.21), pink (.26), white (.33)
As you can see, the yellow current is much higher than the others. I like the various colors, but don’t like how inefficient the yellow is. Maybe I’m having bad luck with where I’m buying them, or perhaps yellow is just inefficient.
Nice measurements!
Yellow is indeed doomed, they are inefficient. I like the colour and I have used them for the switch of a C8F, looks really cool, but they drain the battery a lot faster for the same brightness as other colours. Blue and pink and white have similar current because all three are a blue led. Orange is also pretty inefficient, while red (not in your list) is much more efficient, I expect it to end up at .20 in your list.
Warm white is good alternative and it's few times more efficient.
Didn’t know red was more efficient than orange djozz - so I may swap them out, or add red to another flashlight. And good tip led4power to use warm white instead of yellow - I may order some. When my new yellow LEDs arrive, I’ll see if they are any better.
I did try putting some layers of yellow plastic sheets over the white LEDs, but it barely made the tailcap yellow. Certainly not as yellow/gold as the yellow LEDs.
Another great BLF innovation.
I tried this on a Convoy S2+ with 18350 tube. Took awhile to get the right combination, thought I’d share what worked for me.
I’m using a BLF X6 driver that comes with a attiny25 and Bistro as the UI.
I used the lighted tail switch from fasttech.
The driver has a 470 ohm bleed resistor already installed. The lighted switch has 2- 330 ohm resistors and blue led’s already installed.
These two together would not work correctly running Bistro. It couldn’t detect the off time, no memory and no medium press.
What finally did work, using the 330 ohm resistor from the switch on the driver as the bleed resistor and changing both switch resistors to 10k.
The” banggood lighted switch”:Astrolux SC / SS / S2/S3 BLF X5/X6 Taschenlampe 2 LED Beleuchtung Schalter für DIY Sale - Banggood Deutschland-arrival notice-arrival notice may work as is, from the pics it uses 2-15k resistors.
Should work without a problem
I use two 22K resistors and two blue LEDs on the original switches of BLF X5/X6 kit (wood box)
My warm white LEDs finally arrived. I put them in a Convoy S2. The S2 lighted switch mod was a lot more involved than an S2+, but worth the effort for the extra throw.
Overall warm white LEDs are good alternative, but not nearly as colorful as the yellow LEDs. Despite the loss in color, the efficiency of the warm white LEDs is worth it to me. 0.99 mA for yellow vs 0.31 mA for warm white is a huge difference - that’s almost a year longer with an NCR18650B battery.
Yellow left, warm white middle, white right:
And finally, I put in a red lighted switch in a Convoy S2+. I think the red looks very nice. It measures 0.46 mA, so a little better than orange at 0.56 mA.
That’s it for now! I feel I went a little overboard with these, but each is unique with different combinations of hosts, LEDs, tints, and beam patterns.
Looking good!
Small update to OP to add links to Led4power and Lexel’s versions before I disappear for another few months 
Thanks PD!
Feel free to update that post with my image that is not on PhotoBucket, but a hosting site that actually works……
It’s a small filesize, so it should fit in the collage nicely.
~D
*edit, second try on the link. This should be direct, as opposed to a resized link
shows “Unrecognized url ”
Teaser:
Hopefully this experiment goes as planned
Has anyone completed one of these yet on a Tool AA?
I need to find clear tailcaps to fit one. I don’t have mine in hand yet. Are they 12mm wide? How tall is the button, 5.5 or 7.5mm? It looks like KD did have some 12mm, but maybe not in clear :weary:
KD did stock some green GITD caps, 12mm x 5.5 I believe.
With blue lighted switch.
