The QR code on the last page of the user manual points to this thread and we started to add some content:
- Post 2: Some useful links. The user manual and joechina’s cheat sheet can be found there, among others.
- Post 3: VOB’s video guide for the GT and JasonWW’s series of NarsilM videos are in post 3.
- Post 4: A basic FAQ.
- Post 5: Manual in text format for use with Google Translate.
- Post 7: After-market accessories for the GT.
Please try to stay constructive, on topic and concise in this thread so that it does not balloon to something unusable. (No discussions regarding ordering, shipping, payments, etc.)
The group buy closed on 5 Jan 2018. Production is ongoing and orders are being filled as the GTs roll off the assembly line. The main discussion thread is here:
The main GT thread
Thanks!
Team-Giggles

Official GT team user account.
This account is NOT actively monitored and PM's have been disabled for the time being. Contact Neal, Texas_Ace or one of the other Team members directly if you have questions about your order.
User manual
BLF-GT user manual draft13.pdf
(The first production run shipped with revision 12 of the manual. The revision 13 changes are minor.)
Chinese translation by steel_1024:
BLF-GT Chinese user manual V1.2
Russian translation by Narmattaru
Joe’s excellent cheat sheet for the GT
Cheat sheet
NarsilM firmware development thread
NarsilM thread
NarsilM 1.2 source code and ready-to-flash HEX files
NarsilM 1.2 files
Texas Ace’s review of the final prototype before production started. Your light should look pretty much like this:
Prototype 2 review
VOB’s un-boxing video
Maukka’s test of the stock LED tint and finds it to be nearly perfect!
Stock XHP35 HI 4000k emitter tint test
Official GT team user account.
This account is NOT actively monitored and PM's have been disabled for the time being. Contact Neal, Texas_Ace or one of the other Team members directly if you have questions about your order.
Video guides
Vestureofblood UI interface video on the GT:
JasonWW produced some good guides regarding general NarsilM use. Note that the GT uses a later version of NarsilM, so there are some minor differences:
Narsil Part 1 – Ramping and Features
Narsil Part 2 – Strobes and Blinkies in Ramping
Narsil Part 3 – Turn On and LVP in Ramping
Narsil Part 4 – Using Mode Sets
NarsilM Part 5 – Mode Sets Strobes and Special Features
and GT-specific: BLF GT with NarsilM v1.2 – new strobe modes
How to Change Menu Settings in NarsilM (Q8)
Official GT team user account.
This account is NOT actively monitored and PM's have been disabled for the time being. Contact Neal, Texas_Ace or one of the other Team members directly if you have questions about your order.
FAQ
General
Post in the main GT thread saying that you want one (or more). Then wait for a private message with further instructions. It may take a few weeks before you can make the purchase, because production is slow.The group buy closed on 5 Jan 2018. Lights continue to ship as they are produced, for those already in the group buy. We expect the GT to be available for retail sale at some point in the future.Emitter and output
Cree XHP35 HI, D4 flux bin, 4000 K CCT.
Texas Ace did a detail review here:
GT LED review
No, not really. It’s already driven at 2.5 A, which is just shy of the peak for the GT’s emitter. There’s very little to be gained from giving it more power; it’ll mostly just produce more heat.
Could be caused by several things…
Try an Oslon Black Flat for maximum throw. The hotspot will be tiny though, and the driver may need to be replaced or modified (TBD).
Try a 12 V XHP50, XHP50.2, XHP70, or XHP70.2. It will decrease throw though, and the driver’s sense resistor should be changed to increase power to ~5 A. (We are also looking at cooler running options for the FET and inductor.) Bigger hot-spot, more lumens, less lux. Texas_Ace tried it and says the result is nice. Using 8 cells is strongly recommended for this.
The stock tint is a great tint for real qorld performance but it is not for everyone. If you want to change your tint you can swap in any XHP35 you desire. A good source for XHP35 LED’s is RMM here on BLF. If you send him your stock mcpcb, he will even reflow the new LED on it for you.
Driver and firmware
The firmware bug is just a wrong ‘fuse’ setting on the micro controller. The low fuse was left at the default value of 62, instead of E2. This sets the MCU to run at 1 MHz, instead of the intended 8 MHz. There are no reported cases out in the wild yet. Normally when the battery tube is tightened down the light will flash twice to confirm power. If these two flashes take more than 3 s to complete, you have the bug.
Please see the OSHPark page for the driver here:
https://oshpark.com/shared_projects/6sLsSB1M
From a post here :
Its a proper ‘buck’ driver.
The FET is pulsing the inductor and the inductor, by nature, outputs a DC current proportional to the duty cycle of the FET. (Not to be confused by the PWM output of the tiny85.) The inductor is the big black cube on the board, and is basically copper wire coiled around a ferrite core.
The brains of the buck operation is that small chip sitting next to the sense resistor. The tiny85 simply generates a 0-1.24 V ‘set-point’ for the buck chip. The buck chip compares this set-point with what it measures across the sense resistor and then does its thing to put out the requested amps.
Some things to note:
Officially 20 V, as per the silk on the back of the driver. It should survive up to 24 V, limit being the MIC5235 LDO used for the MCU. Main power capacitors are 50 V rated, but C1 was specified for only 25 V. Going above 25 V calls for a 40 V FET, whereas the stock FET is 30 V rated.
That would be R11, the big (2512 package) resistor. Stock value is 0.091 ohm. Maximum output current is approximately:
2.5 A
From the user manual, page 6:
Disable MOON mode and you will be good to go.
Note that these voltages can be ~0.05 V per cell off in either direction, depending on the component tolerances and temperature. These voltages are monitored under load and cells will read higher when removed and measured outside the light.
Using four Samsung 30Q cells (3000 mAh) gives about 45 minutes of regulated 2 A output, followed by another ~30 minutes of drooping output. Using eight cells doubles this time.
MRsDNF’s run-time tests with four cells
Body / host
It is translucent black, the green back light is visible in a dark location only. If you received a light with an opaque black button we will work with LT to correct it.
12 mm. These are available online, but less common than the standard sizes.
The tail-end attachment point can rotate inside the tail cap.
There may be a pinched or insufficiently-lubed O-ring inside. If you remove the Lumintop sticker inside the tail-cap, the parts should unscrew (reverse-threaded), and then you should be able to check and lube the O-rings.
The driver compartment and the reflector housing are two separate pieces that screw together. It is difficult to have this align and it was never intended to align.
No. But they are tightened down well and especially the bezel can be a tough one to unscrew due to its size.
[Edit 2018-01-11: Driver and run-time details added]
Official GT team user account.
This account is NOT actively monitored and PM's have been disabled for the time being. Contact Neal, Texas_Ace or one of the other Team members directly if you have questions about your order.
GT user manual (draft 12) in text format (for Google Translate)
Thank you for supporting this BLF community project. The GT was designed by BLF, for BLF, and brought to life by top-tier manufacturer Lumintop. We trust it will serve you well in whatever your endeavors might be!
– the BLF GT project team
Safety precautions
Quick start
Default UI: Smooth ramping
This feature-rich UI provides for smooth ramping of the light output between 0 and 80%, with an easily-accessible 100% TURBO mode.
single-click the button, GT turns ON using the previously used light output level
press&hold button
while ramping in one direction, release button briefly and press&hold again
double-click
single-click
from OFF: press the button and release as soon as the GT turns on
double-click for TURBO, and then double-click again
(Use single-clicks to cycle forward through the different types of strobes, but you have to be quick: If resting on a strobe longer than 1.2 s it locks in and the next single-click is OFF. Press&hold at any time to cycle backwards through the strobes.)
Battery status: triple-click (4 blinks, a short pause, then 1 blink would indicate 4.1 V average per cell, for example)
four clicks to disable the GT, same to re-enable the GT
five clicks (loosen and re-tighten the tail-cap to return to normal operation)
triple-click (battery status mode), then double-click (driver temperature mode), double-click again (firmware version mode), then press&hold for about 2 s. Four blinks confirm a successful reset.
Alternative UI: Mode-sets
The GT is factory-set to operate using the contemporary RAMPING user interface, as described in the previous section. However, the GT can also be operated using a more conventional MODE-SET style user interface. (See next section for detail on how to set UI options).
Using the MODE-SET UI the output does not ramp, it steps from one mode to the next using single-clicks.
single-click
single-click before the current mode ‘locks in’ (1.2 s)
press&hold
from OFF: press&hold
single-click button, after resting on a mode more than 1.2 s (mode locked in)
press&hold
(Use single-clicks to cycle forward through the different types of strobes, but you have to be quick: If resting on a strobe longer than 1.2 s it locks in and the next single-click is OFF. Press&hold at any time to cycle backwards through the strobes.)
Battery status: from OFF: single-click followed by press&hold (4 blinks, a short pause, then 1 blink would indicate 4.1 V average per cell, for example)
Advanced operation
By default the GT firmware is set to suit most users and applications, but several settings are user-configurable. To enter the configuration settings, press&hold the button for about 8 s (3 s if in the MODE-SET UI), do not release until a double flash followed by a single blink is seen. The single blink is the prompt for the first setting. Click the button as many times as required for that setting, or leave the setting alone and simply wait for the next double flash, this time followed by two blinks, indicating that we are now at setting #2, etc.
The GT confirms each click with a blink. A press&hold skips to the next setting. A continuous press exits the setup menu completely. Four blinks indicate that the setup is completed.
The available settings differ, depending if the GT is currently set to the RAMPING UI or the MODE-SET UI. Note that changing setting 1 flips to the other UI and immediately kicks you into the table for that UI:
If [temperature] is selected for auto step-down, the GT goes to 100% output. Leave the GT to heat to the desired limit, and then click to set that temperature as the trip point (the GT is huge, so this can take 20 minutes or longer, use fresh cells for this). Or click within 5 s to keep previous setting.
The mode-sets have been selected to suit a high-power thrower like the GT:
Modes in sets 5, 6, 11 and 12 are equally-spaced on a cube-root curve (considered an ideal mode-spacing by many).
Note that MOON mode is enabled by default, adding one extra mode (mode 0) to the above.
Pre-programmed strobes:
Additional UI settings are available to control the button back-light. While in the battery check mode, press&hold the button. A double flash followed by a single blink is again the prompt for the first setting:
Specifications
12 V Cree XHP35 High Intensity, neutral white, mounted on copper DTP MCPCB
Flux: >2000 lm
>1 Mcd (ANSI throw >2000 m)
Tom E’s open-source NarsilM v1.2
Four or eight button-top 18650 cells (4S1P or 4S2P). Protected cells are recommended. Cells are not included.
35 W, 2.5 A regulated buck driver with conversion efficiency that exceeds 90%. Parasitic drain while OFF is ~150 μA (~250 μA with button back-light on).
118 mm ID, aluminum, smooth finish
Glass with anti-reflective coating
Aluminum with Type III hard-coat anodizing
Standard 1/4 inch threaded (1/4-20 UNC)
Tactile with back-lit rubber boot
Equivalent to IP65, do not immerse in liquids
Approximately 1.8 kg without cells
135 mm Ø head x 315 mm length
GT support thread:
http://budgetlightforum.com/node/57676
GT main thread:
http://budgetlightforum.com/node/50303
[Edit: 2018-01-11: Added the two thread links]
Official GT team user account.
This account is NOT actively monitored and PM's have been disabled for the time being. Contact Neal, Texas_Ace or one of the other Team members directly if you have questions about your order.
So what does the team do on mars?
Accessories for the GT
Thank you joechina for this compilation:
https://m4dm4x.com/blf-gt-bag-cap/
Feeler thread
Amazon link
More options
http://budgetlightforum.com/comment/1248124#comment-1248124
http://budgetlightforum.com/node/55821
http://budgetlightforum.com/node/58245
http://budgetlightforum.com/comment/1253930#comment-1253930
https://www.amazon.com/LensCoat-LCH2XLBK-Hoodie-Large-Black/dp/B0087N28Y8/
http://budgetlightforum.com/comment/1272499#comment-1272499
Official GT team user account.
This account is NOT actively monitored and PM's have been disabled for the time being. Contact Neal, Texas_Ace or one of the other Team members directly if you have questions about your order.
[reserved]
Official GT team user account.
This account is NOT actively monitored and PM's have been disabled for the time being. Contact Neal, Texas_Ace or one of the other Team members directly if you have questions about your order.
[reserved]
Official GT team user account.
This account is NOT actively monitored and PM's have been disabled for the time being. Contact Neal, Texas_Ace or one of the other Team members directly if you have questions about your order.
[reserved]
Official GT team user account.
This account is NOT actively monitored and PM's have been disabled for the time being. Contact Neal, Texas_Ace or one of the other Team members directly if you have questions about your order.
Please don’t post it if you subscribed.
Please keep this thread clear of any ‘offtopic’ chatter.
Thank you
Got mine today. My switch LEDs are different brightness levels like someone mentioned before. Not sure if it bothers me though. Anyone else have the same issue?
FAQ: How can I get a BLF GT?
FAQ: Can I get more throw if I drive the emitter harder?
FAQ: Why is my lux meter showing me less than 1.2 Mcd for the GT?
FAQ: How can I mod it to increase throw?
FAQ: How can I mod it to increase lumens?
FAQ: My tailcap ring doesn’t want to spin. Help?
Thanks TK! Done and done into post 4.
My OSH-Park boards
There’s another question I’ve been asked a few times, but it’d probably be out of place in the main list…
FAQ: When will other firmware be available?
Google Translate does not translate PDF files
Any solution for non-English speakers?
EDIT
Solved. … http://budgetlightforum.com/comment/1231963#comment-1231963
Thank you very much.
Sorry for my bad English
(google translator) , (https://www.deepl.com/translator)
Please see if post 5 is useful. (Still need to somehow add the various tables to it.)
Official GT team user account.
This account is NOT actively monitored and PM's have been disabled for the time being. Contact Neal, Texas_Ace or one of the other Team members directly if you have questions about your order.
Either I have the wrong switch cover, or my LEDs are so dim that you can’t tell they’re working unless you’re in a dark room or at night, but I’m beginning to think it’s the LEDs
Hopefully TA can chime in, most of the team lights shipped with opaque button boots.
It is supposed to be very dim, as mentioned in the FAQ above.
TwoThree ways to have it brighter:Edit: For the mismatched LEDs, that can happen with LEDs wired in parallel. Still preferable to having one off-center LED I guess. It may also simply be the way the rubber boot is orientated. A simple hack here would be to rewire the LEDs in series and change R8 to 10k (MCU is running at 5 V on GT, so there is enough voltage to do this). Bonus, double brightness for same parasitic drain.
My OSH-Park boards
In post 5, specifications, emitter, could we add the details that it is a D4 bin and 4,000k color temp?
Also, I have been asked if the strobe modes are using the 2A, 2,000 lumen mode or the turbo 2.5A, 2,500 lumen mode. Does anyone know?
Texas Ace Lumen Tube and JoshK Sphere calibrated with Maukka lights
Click this to go to signature links. I'm still around, just not reading many new threads.
It seems a handful of black boot slipped through to normal people as well. Neal is taking care of them on a case by case basis.
You are also spot on with the rest of the details.
Texas Avenger Driver Series
My LED Test series - XP-L2 V5 - Nichia 219C 90+ CRI - Latticebright "XM-L" - XHP35 & PWM efficiency - XHP50 - XP-L V5 - XM-L2 U2 - XP-G3 S5 - XP-L HI V2 - Oslon Square & direct comparison to Djozz tests - Nichia 319A - Nichia 219B 9080 CRI - Nichia 219C D320 - Nichia 229AT - XHP70.2 P2 - XHP50.2 J4 - Samsung LH351D
Easy comparison tool for all my LED tests
Post 5 is a verbatim copy of the printed manual so it should stay as is. No problem to add the bin info to the FAQ though.
For the strobes, these are at 2.5 A. This is from the source code:
Basically the buck chip is set to full power in the first line and then alternatively enabled/disabled in the next three lines.
Official GT team user account.
This account is NOT actively monitored and PM's have been disabled for the time being. Contact Neal, Texas_Ace or one of the other Team members directly if you have questions about your order.
Is there a way to have the lighted switch stay on when the light is turned on? Having a lighted switch is just as helpful when you want to change output levels or turn the thing off as it is when you want to turn it on.
There’s no option for that. You’d have to manually run a new wire to keep it powered all the time, so you’d lose the “indicator” function. No big deal as I have two lights where the switch stays on all the time.
Texas Ace Lumen Tube and JoshK Sphere calibrated with Maukka lights
Click this to go to signature links. I'm still around, just not reading many new threads.
If the GT’s lighted switch is controlled by the MCU, it should be possible to change its behavior via firmware. From the way the question is written though, I get the impression that maybe that’s not how the switch light works on this model?
I thought it worked like the Q8, but now I’m not sure.
Yes it can be changed by firmware, but not the existing firmware as it has no options to make the light always stay on. I think Tom E said he was going to possibly add the option to make the light always stay on in a future version of NarsilM.
Texas Ace Lumen Tube and JoshK Sphere calibrated with Maukka lights
Click this to go to signature links. I'm still around, just not reading many new threads.
For me this would be great. I just came in after using the GT and with the temperature around -10F and I was wearing gloves which made locating the switch by feel was impossible. I had to take my glove off to find the switch, kinda cold on bare fingers holding an aluminum light.
You could wait a while and see if it gets done then reflash the driver. Personally I would just pop the driver out and move a wire. You could do that now. I haven’t looked to see if a resistor will be needed or not. I plan to swap the leds and switch cover so I’ll write up all that info for anyone else.
Texas Ace Lumen Tube and JoshK Sphere calibrated with Maukka lights
Click this to go to signature links. I'm still around, just not reading many new threads.
The switch control code is already written. I mostly just need to adjust the ramp values to work on the GT’s driver, and check the calibration in general. I doubt it’ll take long. I could probably even do it without hardware, but I make no guarantees that it’ll actually work.
The method I’ve been using to control the switch light is:
It seems to work well on the Q8, but I hear the GT’s boot is a lot darker so I’m not sure the “low” brightness will be of any use.
This sounds great! The thought of me “going in” with a solder iron and changing things feels like a recipe for disaster to me. What is involved in “re-flashing” the driver? I know my way around the numbers concerning lights, led’s and batteries, but I am a total noob when it comes to drivers and all of the other internal electronics you guys talk about that make my eyes glass over.
If Wisconsin was a little closer to Houston I would stop buy and have you show me hows it’s done. I need to buy a couple of cheaper lights to take apart and experiment with.
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