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

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)

FAQ

General

• How can I get a BLF GT?
  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

• What LED is used in the GT?
  Cree XHP35 HI, D4 flux bin, 4000 K CCT.
  Texas Ace did a detail review here:
  GT LED review

• Can I get more throw if I drive the emitter harder?
  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.

• Why is my lux meter showing me less than 1.2 Mcd for the GT?
  Could be caused by several things…
  • Lux meters usually read higher for cool white lights, so the GT’s warmer tint could be tricking the meter. This doesn’t mean it won’t throw as well as intended, just that the meter isn’t very good as measuring it.
  • The beam doesn’t fully collimate until ~20+ meters, so it may be necessary to increase the distance between the light and the meter for a good measurement.
  • The light might be running at 2.0 A instead of 2.5 A. Be sure to take measurements on turbo (which is above the normal output modes; double-click to access turbo).

• How can I mod it to increase throw?
  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).

• How can I mod it to increase lumens?
  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.

• How do I get a different tint LED?
  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

• Do I have the firmware bug?
  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.

• Where can I find information on the driver / get a driver PCB?
  Please see the OSHPark page for the driver here:
  https://oshpark.com/shared_projects/6sLsSB1M

• How does the driver work in layman’s terms?
  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:
  • There is some PWM happening in the driver, but for most output levels the LED current is almost pure DC
  • To get to the very low modes, it does output PWM to LED (modes below 10%, or 0.25 A). This is under the control of the tiny85 when we go PWM and when we go DC, so there is flexibility here for people doing their own firmware.
  • Battery current is not same as LED current. Like for a transformer, the ratio depends on input vs. output voltage: Iled = Ibat * (Vbat/Vled) * Driver efficiency
  • Driver efficiency is around 92%, depending again on voltages
  • The FET is a p-type, not our typical n-type. It is being pulsed at up to ~600 kHz, so it also needs to be much faster than our typical ‘direct-drive’ FETs.

• What is the maximum input voltage that the driver can take?
  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.

• Where is the sense resistor and what is the formula for output current?
  That would be R11, the big (2512 package) resistor. Stock value is 0.091 ohm. Maximum output current is approximately:
  

  Imax = 0.248/R11 - Ir/2
  where Ir = 0.3 on the stock driver
  

• What output current is used for the strobes?
  2.5 A

• I set my GT for the mode-set UI, set 7, but I get two modes instead of the expected 100%-only mode?
  From the user manual, page 6:
  

  Note that MOON mode is enabled by default, adding
  one extra mode (mode 0) to the above.
  

  Disable MOON mode and you will be good to go.

• The GT has low voltage warning and shut-off. At what battery voltages does this happen?
  • At 12.0 V (3.0 V per cell) the GT will blink the main LED and step down in power. It will do this repeatedly until the battery voltage recovers above 12 V.
  • At 11.2 V (2.8 V per cell) the GT will blink rapidly and shut down the main LED.
    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.

• What is the run-time of the GT on a set of fresh cells?
  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

• Why is the rubber boot for the button not transparent?
  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.

• What is the size of the rubber boot for the button?
  12 mm. These are available online, but less common than the standard sizes.

• Why do the front and back lanyard attachment holes not line up?
  The tail-end attachment point can rotate inside the tail cap.

• My tailcap ring doesn’t want to spin. Help?
  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.

• Why do the font lanyard attachment hole not line up with the button?
  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.

• Are any parts of the host glued together?
  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]

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

• Use only reputable 18650 cells of known origin. Protected type cells, based on Samsung, Panasonic/Sanyo, Sony or LG cells, are recommended.
• Use a reliable battery charger. Never over-charge or over-discharge cells.
• Cells are used in series, not parallel. It is therefore important that all cells are identical: Same make, model, capacity, age, used cycles, and furthermore charged to the same level.
• Remove and recharge cells when the low voltage indication is given by the GT (repeated step-downs in light level and eventual shutdown of the light).
• The extraordinary energy density that 18650 cells offers also means that hazardous conditions are created when a cell is short-circuited or damaged. Always treat cells with respect and properly dispose of damaged cells.
• The GT is a very high-intensity flashlight. Do not point the GT directly at a person, animal, moving vehicles or flammable materials.
• When running at higher output levels the head of the GT will slowly heat. This is normal. In warmer ambient conditions this temperature may exceed 60ºC, so please take the necessary precautions when handling the GT.

Quick start

• Load the cell cradles with four 18650 cells each. Note that the cradles require button-top type cells. The GT is designed to work with either or both cell cradles populated. Take care to observe the correct polarity for each cell.
• Unscrew the tail-cap and insert both cradles. Again take care with the polarity: Arrows on the cradle rods must point towards the head of the GT. If populating only one cradle we recommend placing it towards the rear, so that the GT balances better in the hand.
• Screw the tail-cap back. The GT will flash twice when electrical contact is made. Continue to tighten the tail-cap to a gentle stop. Do not over-tighten.
• All functions are performed using the single side button. Note that pressing this button continuously for more than 8 s enters the UI configuration settings (indicated by the light blinking). If this is done inadvertently, exit the configuration settings by simply releasing the button briefly then pressing it again continuously for about 4 s until all the resulting blinks stops.
• The GT comes factory-set to use the RAMPING UI: From OFF, press&hold the side button. The light output will ramp up from a very low level to full power. Release the button when the required light level is reached. (The full ramp takes about 3 s.) Use a single-click at any time to turn the GT OFF. Please see below for further details.
• There is a very small drain on the battery while OFF. This should not be of any concern, but we recommend removing the cells (or partially loosening the tail-cap) if the GT will not be used for several months.
• By default the button back-light is illuminated while the GT is OFF. This is normal and is done to easily locate the button in a dark environment. Turning the GT ON, then OFF, in rapid succession, disables the back-light until the next use. This is also normal.
• For the complete user manual and any questions you might have about your GT, please visit the GT support thread on BLF. The link is on the last page of this manual.

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.

• Turn the GT ON:
  single-click the button, GT turns ON using the previously used light output level
• Ramp light level:
  press&hold button
• Reverse ramp:
  while ramping in one direction, release button briefly and press&hold again
• Instant TURBO:
  double-click
• Turn the GT OFF:
  single-click
• MOON mode:
  from OFF: press the button and release as soon as the GT turns on
• Strobes:
  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)
• Electronic lock-out:
  four clicks to disable the GT, same to re-enable the GT
• MOMENTARY mode:
  five clicks (loosen and re-tighten the tail-cap to return to normal operation)
• Factory reset:
  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.

• Turn the GT ON:
  single-click
• Next mode:
  single-click before the current mode ‘locks in’ (1.2 s)
• Previous mode:
  press&hold
• Last mode [100%]:
  from OFF: press&hold
• Turn the GT OFF:
  single-click button, after resting on a mode more than 1.2 s (mode locked in)
• Strobes:
  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)
• Electronic lock-out: from OFF: double-click followed by press&hold, same to re-enable the GT
• Factory reset: from OFF, single-click followed by a press&hold (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.

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:

RAMPING user interface settings
Setting		Function		Clicks
1		User interface		1: MODE-SET 2: RAMPING [default]
2		MOON level		1-7 [default 3] 
3		Auto step-down		1: Disable 2: Temperature [default]** 
					3: Timed, requires another 1-6 clicks for 60s/90s/2m/3m/5m/7m respectively
4		Strobes			1: Disable 2: Strobe 1 only 3: All strobes [default]

MODE-SET user interface settings
Setting		Function		Clicks
1		User interface		1: MODE-SET 2: RAMPING [default]
2		Mode-set		1-12 [default 4]
3		MOON mode		1: Disable 2: Enable [default]
4		Mode order		1: Low to high [default] 2: High to low
5		Mode memory		1: Disable [default] 2: Enable
6		MOON level		1-7 [default 3]
7		Auto step-down		1: Disable 2: Temperature [default]**
					3: Timed, requires another 1-6 clicks for 60s/90s/2m/3m/5m/7m respectively
8		Strobes			1: Disable 2: Strobe 1 only 3: All strobes [default]

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:

Mode-set no.	Modes [% of light]
		1	2	3	4	5	6
Sets 1 to 6:  100% = 2.0 A LED drive
1		100					
2		25	100				
3		11	33	100			
4		12.5	25	50	100	[default]
5*		1	7	22	52	100	
6*		1	5	15	32	60	100
Sets 7 to 12:  100% = 2.5 A LED drive
7		100					
8		25	100				
9		11	33	100			
10		12.5	25	50	100		
11*		1	7	22	52	100	
12*		1	5	15	32	60	100

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:

Strobe	Type
1	16 Hz
2	Police strobe (dual frequency)
3	Biking (low light with hi-vis stutter)
4	2 s beacon
5	10 s beacon

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:

Advanced UI settings
Setting	Function				Clicks
1	Button LED on while GT OFF		1: Disable 2: Enable [default]
2	Battery level blinks on button LED only	1: Disable [default] 2: Enable
3	Button LED				1: Disable 2: Enable [default]

Specifications

• Emitter:
  12 V Cree XHP35 High Intensity, neutral white, mounted on copper DTP MCPCB
  Flux: >2000 lm
• Intensity:
  >1 Mcd (ANSI throw >2000 m)
• Firmware:
  Tom E’s open-source NarsilM v1.2
• User interface:
  • By default the GT is set to use the very intuitive Narsil smooth RAMPING UI. Instant access to a 2.5 A TURBO mode is also provided.
  • A more conventional discrete level MODE-SET UI is available as an alternative. Any one of 12 pre-defined mode-sets can be selected.
  • MOMENTARY mode is useful for signaling purposes or rapidly/briefly lighting up targets.
• Battery:
  Four or eight button-top 18650 cells (4S1P or 4S2P). Protected cells are recommended. Cells are not included.
• Driver:
  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).
• Reflector:
  118 mm ID, aluminum, smooth finish
• Lens:
  Glass with anti-reflective coating
• Body:
  Aluminum with Type III hard-coat anodizing
• Tripod socket:
  Standard 1/4 inch threaded (1/4-20 UNC)
• Button:
  Tactile with back-lit rubber boot
• Ingress rating:
  Equivalent to IP65, do not immerse in liquids
• Weight:
  Approximately 1.8 kg without cells
• Dimensions:
  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]

Accessories for the GT

Thank you joechina for this compilation:

• Neal/m4dm4x’s bag and lens cap
  https://m4dm4x.com/blf-gt-bag-cap/
  Feeler thread

• Op/Tech neoprene hood hat
  Amazon link
  More options

• DIY lens cap
  http://budgetlightforum.com/comment/1248124#comment-1248124

• Thread for carry/storage cases
  http://budgetlightforum.com/node/55821

• Thread for shoulder straps – the GT gets heavy (and cold in winter!)
  http://budgetlightforum.com/node/58245

• Button boot dimensions
  http://budgetlightforum.com/comment/1253930#comment-1253930

• LensCoat Hoodies
  https://www.amazon.com/LensCoat-LCH2XLBK-Hoodie-Large-Black/dp/B0087N28Y8/

• Fabric Shrink Tube on the battery tube
  http://budgetlightforum.com/comment/1272499#comment-1272499

[reserved]

[reserved]

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pepinfaxera wrote:

Team-Giggles wrote:

User manual BLF-GT user manual draft13.pdf

Google Translate does not translate PDF files
Any solution for non-English speakers?

Please see if post 5 is useful. (Still need to somehow add the various tables to it.)

JasonWW wrote:

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?

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:

void Strobe(byte ontime, byte offtime)
{
	FET_PWM_LVL = 255;
#ifdef GT_BUCK
	ONE7135_PWM_LVL = 255;	//  for GT-buck
	_delay_ms(ontime);
	ONE7135_PWM_LVL = 0;		//  for GT-buck
#else	
	_delay_ms(ontime);
	FET_PWM_LVL = 0;
#endif
	_delay_ms(offtime);
}

Basically the buck chip is set to full power in the first line and then alternatively enabled/disabled in the next three lines.