Over engineering a flashlight (that nobody wants)

Flashlight Modding and DIY Parts
1

Hello!
First of i will have to say, i know what i am dooing fairly well on the electronic side.
Designing a circuit, PCB layout and programing i have been dooing for years now.
Please do not think that i am asking because i have no idea about this stuff and need someone to do the work for me. :slight_smile:

A few days ago i hatched the idea to maybe build myself a flashlight with a few features that have been determined from years of camping.

Build in battery (single LiIo cell, serviceable/replaceable after end of life, probably a 18650)
Build in charger with micro USB port
Build in fuel gauge/battery charge indicator
Wide beam only, somewere around 130°, never had much use for tight beam flashlights
Maybe a light difusor but no lenses
High efficiency and high-ish runtime at low end power levels
Rectangular enclosure, i do not like round lights.
Waterproof
Low-cost-ish, so i can have multiple units running
About 2700K color temp, warm and not cold and dead
Ultry low power mode to run the thing at a few lumens for days as a tent light.
About 130 Lumens/Watt efficiency.

I ran a few tests and it seems that about 200 lumens with 130° beam angle produces the light i would like to have.
The max brightness i want is about 500 lumens, perhaps. Will have to do some real world testing to be sure.

And the most important bit, i would like to have two buttons, one On/Off and one “analog” dial for the brightness.

The brightness control i am a bit unsure about, at the moment i favor a magnetic switch based on a hall effect sensor to achieve complete water resistance and a completely sealed enclosure.
Charging through some protected/isolated terminals, i am thinking about either just TVS diodes with PTCs and maybe reed switches to disengage the charge terminals during normal operation.

On the actual LED i am a bit unsure, my favorite so far is a Nichia NF2L385AR wich sits beside on on my table.
I am thinking around 4 emitters in series for “cosmetic” reasons, do not ask why it is a silly idea of me :slight_smile:

A charge indicator that display the runtime, using a fuel gauge to get a real battery level and not estimation.
Not sure about the display yet, i favor 10 LEDs with each one indicating 10% of real charge wich only turn on when you ask for it.

A rough estimation give me about 5mA of current consumption for the electronics, wich should be ok and 200mA to 300mA for the LEDs at 12V to 24V wich is… challenging. I have not found a suitable IC that does that, but i have not looked that good yet as well.

If someone is still reading, what do you think? :slight_smile:

2

I’ll take one while you’re at it. I like what you like, 500 lumens; 130 degree beam angle; and 2700K.

3

I like the idea. Especially the warm incan-ish tint for camping.

4

Forgot to say Welcome!

5

Following

6

Welcome to BLF!
Wauw sounds like an awesome light

7

Hello and thanks for your replys!
Would anyone have a recomendation for a suitable driver IC?
Onsemi has a few interesting chips, the NCP3066 seems to be a contender but is hard to get.
The supply current is rather large at 7mA.

Skiming TI, Maxim,Analog and Linear i could not find something interesting.
Might have to have a better look.

8

Welcome! Lot of ideas here I like. I've thought of exactly that switch arrangement - ON/OFF and mag slider for brightness.

Actually what I have in my hand right now is pretty close, just that the LED's setup is different - cooler tints, 3 LED's in parallel, 4 18650's in parallel, and running firmware that uses just one electronic switch, but has a smooth ramping ability, triple-click that blinks out the voltage level of the batteries (ex; 4.1v blinks out 4 blinks, then pauses, then 1 blink, does this continuously til you click).

I'm using this diffuser: http://www.fenix-store.com/fenix-aod-l-diffuser/, that fits the SupFire M6 perfectly. I bought mine on Amazon for $6. I'm really impressed with how well the diffuser fits the M6, and how well it does in producing a real lantern effect to light up a room or area.

Of course this light can do 5,000 lumens on max without the diffuser, but still, it can do anywhere from sub 1 lumen to 5,000 lumens on a smooth ramp of 150 levels in about 2.4 seconds (source code and manual are posted/published).

This "soup can" style light, like the SupFire M6 is great for very long runtimes on low lumens settings, with multi LED's and 4 cells in parallel. Lot of things you can do with them in customizing. Two projects going on now are a 4X LED customized high amp group buy here:

https://budgetlightforum.com/t/-/39069 (4X Neutral White LED's in the 5000K range or so)

and a pretty cool lantern mod for camping of the same base light here:

https://budgetlightforum.com/t/-/38215

9

For MCU's, the PIC 8 pin MCU's are very popular in stock lights, but we use Atmel's here, the ATtiny13A, 25, 45, or 85, because we know how to wire them up and program them. We use 7135's for regulating and limiting amps, and FET's for max crazy high output. I'm not sure what you will find for LED drivers using a 4.2v 18650 as the power source - no one here uses anything of the sort, not for regular flashlight usage, at least not I'm aware of.

10

Quad’s not a problem to run in parallel rather than series from a single cell. There are some ring mounted Hall effect transistors for dive light drivers and maybe they could be converted to a linear arrangement.

11

There is the Diodes Inc. AL8805 for a buck driver arrangement. Have used it on an adjustable desk lamp, off a solar charged 12V SLA battery, for some time now. The AL8805 powers three XTE’s (3000K) in series.

12

I like one too

How about an arduino nano as driver?

13

With the exception of the rectangular shape it does sound great. Only saying that because I am not familiar with the new shape or why that would be of use? Isn’t it more comfortable to hold something cylindrical for extended amount of time?

14

Maybe a boost driver is required. Here is an interesting candidate TI TPS61500

There are some figures in the data sheet which correlate Vin, Vout (number of leds x Vf), and the expected output current that would be available. So a quad Nichia 219C setup with a single cell is possible?

15

Hello and thank you everybody for the many replys,
did really not expect that many, enjoyed each one!

Personally i do not like round lights because thes roll away, are too long to be suffed away nicely and they do not look like something that could be from star trek. I dont want a light saber, silly reason, i know. :slight_smile:

The single Li* cell is a simple necessity to facilitate the charging over a USB port, there are many other solutions but the Lithium Battery+Linar charge IC is cheap and simple. The Microchip MCP73833 is my go to, it is cheap has a temperature control and a 3 LED status indicator that is somewhat more usefull then just a single charge indicator LED.

As far as the controller is concerned, it should not be one but i will use something atmel. They use too much power but i am used to working with them.
No idea wich one, what i can tell you that i have a few ATTiny13V, ATMega328P, ATMega32U4, ATTiny85 and some others i can not remember. So it would be one of these. Using the 32U4 is tempting but it is a big package and somewhat power hungry.

About the regulator, thank you for suggesting the TPS61500, seems to be suitable.
But after a bit more looking i found something interesting… the TPS6116, this chip has one marvellous feature.
It has build in diming over a one wire signal.

The only problem i have is deciding wich LED driver to try, i have build a dozen or so different DCDC regulator for single cell LiIo use, but a constant current LED driver is new to me :slight_smile:
The TPS6116 may be my best bet so far, low pin and component count, less board space and cheaper.

The rough size estimate i have for now is about 40x20x70mm but i have not thought about that much at all.

16

I am getting chummy with the TPS61165, at 3V input voltage (way past the end of discharge voltage) it can drive 8 LEDs at 100mA in series.

That would yield about 300 Lumens max brightness with 4 of the Nichias, undershooting my goal but still bright enough.
The 100mA is the max i want the Nichias to run at, otherwise the efficiency goes down the drain and they stay cool without much need for heatsinking.

The only alternative would be a Cree XP-G2 R2 but they are damn expensive at 6 bucks.
The Nichias cost about 1€ a piece, the Cree is 6€, that is 4€ vs. 24€ just for the LEDs.

Yea, i know, i could use a single LED high powered one and everything would be good, then it would be a regular flashlight and not the silly contraption i would like to have :slight_smile:

Oh… i dit not say it yet, i know i can run LEDs in parallel but everything in me screams at the thought.
I know it is not a problem to do it when done correctly but… i just can not to peace with that thought. Got to be a series connection.

17

Heat kills. The TPS61500 tssop with power pad pkg. has 1/2 to 1/4 the thermal resistance of the TPS61165 qfn or sot23 pkg. There is a 3A switch versus the 1.5A switch and half the Rdson. So much more likely to achieve 500 lumen? I speculate here as I have no experience with either driver. I did try a LT 1A buck boost driver which came in a 10 pin QFN pkg. and smoked several chips through experimentation though :slight_smile: .

18

Yes, that is right! On the other hand, the 61165 has a digital Interface to enable diming, no need for PWM, the uC can go into shutdown during normal Operation.

At 24V with 0.1A that is 2.4 Watt of power, without opening Excel my gut thinks it should work out.

But, Samples cost nothing and the PCBs are simple enough to etch them at home so I can give several Converters a good try :slight_smile:

BTW. The fuel gauge i want to use is the D2764 from Maxim, i have a Board left over with one so I don’t want to try out something new.
Really expensive but it is accurate enough and has an internal sense resistor that is temp compensated and it brings along a cell protection Front end.
If it were not that bloody expensive i would use it all the time.

19

So… lets start with what i allready have, know and need:

http://i.imgur.com/JShZCpg.jpg

That is pretty much the whole power circuit, there should not really be any need for voltage regulation for the logic side (the mikrocontroller) but im not sure what part i want to use. Some µC need a extra regulator, well see.

20

The form rough size was inspired by this:

Imgur

Just looked for some nice Aluminium extrusions as a case. But that is way down the road. Electronics come first :slight_smile:
The highest capacity18650 i looked up is a INR18650MJ1 at 3500mAh, that would give a Runtime of about 50 minutes at 300 lumens. But my numbers might be completely of…

A full charge would take about 3 hours from a 1.5A USB charger.

Is that a decent number?