You can if you want to, but it doesnt really matter unless it was avery early D4 with the first gen thermal management. Personally if it hasnt been done already id just switch it to Anduril and call it a day.
Check out the first post of this thread. You need to pop out the driver in order to flash the Attiny with a SOIC8 clip.
I’m not looking to take anything apart, but what does switching it to Anduril mean?
Changing the Firmware from one user interface to another. The D4 originally came with a firmware called RampingOS, later batches of the D4 came with an updated RampingOS or optionally Anduril.
If you dont want to take the light apart, you cant update or change anything.
What are the differences in the ramping OS’s, how would I know which I have?
Also, what changes does the Anduril have?
i have the original Emisar D4 that Hank kindly flashed Anduril before shipping it to me in June of 2019. not sure which version. i think the OS is technically for the D4S?
anyway, i want to increase the thermal regulation cutoff. i think it steps down too fast on turbo. but even with watching YouTube videos, i still don’t get it.
anybody have straight forward instructions? i think i have to use my infrared handheld thermometer? i don’t think it’s the OS where you just hold the light and click a button when you think it’s too hot to hold. i’m american, so i only understand Fahrenheit 
i love this light!
If it is Anduril, the code installed on yours is more likely for the D4v2 not the D4S. In any case, just follow the Anduril instructions in the post immediately before yours.
I believe the late production D4 has the D4v2 driver board with pads for flashing. So you basically have a D4v2 engine but without the fancy bits (secondary leds, knurled battery tube, etc.).
I’m guessing the new K1, D4v2 Ti blue swirl and D4Sv2 will have the above version?
They should just do 15+ clicks and it will blink out the firmware date in YYYY MM DD format blinks.
Good tip, is there somewhere that gives date brackets with firmware versions?
i figured it out. i have an infrared thermometer. calibrated the temp to 25C… i did 40 clicks above 30C… so 158 degrees. a little nutty, but i’d turn the thing off way before that. it still steps down… but sucks the battery dry a lot faster. is 40 clicks possible or is there a limit to the thermal cutoff?
70C is the limit. You can click more than that, but that will set it to the max of 70C anyway. If you want to fake it out to get the max set to 85C for example, calibrate room temp to 7C or so. That should help even more. 22C is ~72F (22 * 1.8 + 32).
thanks Tom! yeah, i was wondering about cheating the room temp calibration… but other than experimenting with the”limits”, i realize it’s kinda pointless to make the thing melt in your hand. LOL!
it still dims even in my hand… given it’s RIDICULOUSLY hot when it does it… i assume the light hits an internal temp of 158 degrees on turbo fairly quickly anyway?
Well, probably, but I'm not sure I trust that internal MCU temp sensor much. Can't do much with 4 LED's maxed out in such a small mass with such a small surface - not much of a thermal path, or, the thermal path is so good getting to the outside, that's why it heats up so quick. Gotta take a light like this for what it is - super power in a small package for short uses, or any lower power level you'd like for practical longer term use. For example, a few mins ago I used my EDC18 on a low setting to trouble-shoot my gas furnace. The mag tail meant I could place it perfectly above the area I was working in, and at 100-200 lumens or so, it can run comfortable at room temp.
Better heat sinking of the driver would help - most of these kind of lights don't take the driver heat sinking seriously. More metal to metal contact between the driver and shell would help, as well as potting the driver. Now that we got external pin re-programming capability, potting should be considered.
totally, i LOVE the D4. it’s such an insane little pocket rocket. turbo is mostly for “shock and awe”. but yeah… from moonlight to like 300 lumens. it’s super useful. and the candle light and lightning settings are relaxing. LOL!
You are probably right. It definitely has the pads. Hopefully that means the later attiny chip too.
I’m guessing hank just put the V2 board in with anduril, rather than reflash an old board? If so, nice guy!
It still has that “notch” when the light switches from Regulated to FET. not sure if that means anything.
I kinda want a V2… But there’s nothing wrong with my D4.
About the thermal response, if it regulates down, that doesn’t necessarily mean it has already gotten too hot. It means that it thinks it will be too hot soon if it continues along its current trajectory, and it’s trying to “turn into the curve” to avoid overshooting.
So it can sometimes adjust down before it’s overheated… and conversely, it can sometimes adjust up while it’s still hot, if it thinks it’s cooling off too fast.
Usually this effect is only noticeable during the initial burst at a turbo level, because at that point it heats up very quickly and the estimated future temperature easily goes over the limit. It doesn’t know enough math to figure out that the temperature rise will slow down naturally on its own.
If you update the firmware though, it may behave a little better. The thermal code has been completely rewritten. It’s not perfect, but it seems to behave better and it’s a lot more stable now after it gets close to a sustainable level. Older versions could go too far, overcorrect, and bounce or oscillate sometimes… or even just randomly go on a wild tangent because of noise in the measurements.
It means it switched from regulated to FET. 
It’s like how, on a know to change the panning of a sound from left to right, there’s usually a notch at the center point. It indicates that the adjustment just hit a meaningful level. It could be totally smooth instead, but then it’d be harder to feel where that point is.
I don’t understand the organization of Launchpad very well, but I think this link can help you find what you’re looking for:
https://bazaar.launchpad.net/~toykeeper/flashlight-firmware/fsm/changes/
And I think that’s the development branch, not the trunk. I don’t know if that makes a difference with respect to what Emisar’s ship with.
Thank you TK!
That makes sense. When I double click back into turbo after it started stepping down the first time, it stayed brighter longer once it was already warmed up.
Not sure if I’m slick enough to update the firmware. It does have the pads though.
I might just quit while I’m ahead. Turbo for me is pretty much just for shock and awe for friends. I mainly use the light from about moonlight to 300 lumens. And I find the lightning storm and candle modes really relaxing. Haha!
The turbo level on hotrod lights like the D4 is mostly just intended for burst use anyway, not sustained use. So, ideally, it should only be used for short periods before the user manually sets it back to a sane level. It only takes a moment to see what’s off in the distance, or to make people nearby go “wow”.
Flashlights have reached an odd point in their development, where “brighter” is no longer synonymous with “more useful”. For general daily purposes, usually a couple hundred lumens is enough… and beyond that, the most important traits relate to the size and shape and interface and quality and stuff like that.