Credit card sized light, 1.6mm thick

[balou]

hi,
this design was floating around my head, and then I just had to draw a preliminary sketch in eaglecad. basically it's an ultra-thin (1.6mm, 0.06in) credit-card sized, wallet-conformant flashlight with a very wide beam and an output of guesstimated 24'000mcd

specs:
powered by 4x cr2016 lithium coin cells, two in series. powering 4 samsung 3-chip smd leds.

the base for the whole thing is a 1.6mm pcb, with holes drilled for the coin cells and the leds. contact to the coin cells can be made with a small strip of aluminium or copper foil. as a substitute for top and bottom plates I thought about using pda screen protector foils. they are tough and just a tenth of a mm or so thick. some sort of print-on stickers could also be used, to make a business card with an integrated flashlight.
the switch is a momentary SMD switch by omron which is just 1.3mm thick. btw, the switch is the little thingy on the right. it's sunk in a bit, to make accidental activation in the wallet a bit harder

here's a pic of the led mounting method:

and here's the rough pcb layout:

LEDs: http://www.led-tech.de/de/Leuchtdioden/SMD-LEDs/Samsung-Ultrabright-SMD-3-Chip-LT-1323_1_2.html
SMD switch: http://uk.farnell.com/omron-electro...p/tactile-switch-side-actuated-smd/dp/1333655



so... any comments whatsoever welcome. is there already such a light? (I know there are some which contain a 5mm led and lr44 batteries. obviously they're not really 'credit-card sized'). do you think that such a thin light is a stupid idea?

 

[spencer]

I like the idea of this really thin light. It is similar to another project but much thinner. I like it because you could have one in your wallet. I recommend continuing with this project. Not a stupid idea.

 

[hamheart]

good idea but there is another light similar to this called the chimera mini so you might want to check it out.

 

[balou]

yeah, but the chimera is 5 times as thick
will probably not fit into a wallet anymore

by the way, I just saw that the circles are only 16mm in diameter, they should be 20mm. will correct that tomorrow.

I also thought about a smaller version, maybe 24x32mm, with just a single led and single battery. or a half-credit card sized version with the 4/4 configuration. smaller size would mean that it's less prone to break if you sit on it while its in your wallet, and also lower pcb manufacturing costs (a 100x80mm prototype board costs about 60$ with all tooling fees and shipping included )

 

[clg0159]

Definately a cool design! Have you calculated a runtime on it? FWIW, I generally do not like coin cells b/c they are so expensive.

 

[balou]

runtime will be max 1.5h on idealized energizer 2016 batteries, a more conservative guesstimate would be 1h with real-world battery behaviour and offbrand batteries.

by the way, 20x 2016 coincells are only $3.88 shipped at dealextreme.

energy dissipation of the whole thing would be about 0.75W

but I'd really have to run tests to confirm this... the samsung led datasheet is quite vague about brightness and max power consumption (e.g. they state brightness at 60mA, but half a page above they say that max allowable current is 30mA)


another point: what about chaining all 4 leds and 4 batteries in series to even out Vf differences? anybody got experience with that?


edit:
to put it into perspective with the chimera:
chimera: ~$350, charging circuits, cree led, I guess >100 lumen output
cclight: $20 max, single-use cr2016 batteries, not the most efficient leds, no idea about output, 10 lumen would be great already

 

[spencer]

It says on that site with the LED's that they are 13.5 lumen each so x 4 is 54 lumen. It ends up being 75 lumen a watt so thats not really bad efficiency.

 

[Mosser]

you can already buy a 2mm thick credit card sized torch powered by 2 x cr2016 batteries here in the UK, i was given on for christmas 3 years ago, it was pretty expensive at about £20, but is suprisingly bright and always there when you need it

I think it was made by sinclair, i can do a bit more digging for info if your interested

 

[LouRoy]

This link may interest you:

http://flashlightnews.org/story1071.shtml

Also do a search for Eon flashlight. It is another with a similar idea.

 

[balou]

spencer: kinda overlooked that.... ~50 lumen would be quite bright for such a tiny light

Mosser: do you meat that one: http://www.iainsinclair.com/products/eonclassicintro.html ?
It seems to be 2 or 2.5mm thick at the thinnest point... it's more like 7mm at the thickest point (I guess they use a 5mm led, which has a 5.8mm diam max. then you still need two plastic shells)


One problem that still exists is the switch... I don't know if Farnell even ships to individuals. And the switch is extremely tiny, and momentarily only.

A pressure switch like the sinclair and many cheapo pocket flashlights use is also not an option. Guess what would happen if this light sits in my wallet in my back pocket...

Anybody got an idea for the switch? A switch where you close the contact with your finger would be an idea. But that would need an smd transistor - fingers have to high a resistance to power 4 high power smd leds



edit: I'm curious... would any of you really put a chimera/sinclair eon/other 'credit-card sized' light in your wallet? that would be the size of a stack of about 10 credit cards, whereas 1.6mm is about the size of two credit cards

 

[Sabrewolf]

I have got one in the works that is about 4mm thick.
It will use 2x 200mA li-ion rechargable batts with a
built-in usb charging jack, 2x Nichie GS leds and will
be made of brass or aluminum. But the price would
be about 100 bucks

I do like your 1.6mm light idea though

I really like the walletable idea !!

 

[Sabrewolf]

runtime will be max 1.5h on idealized energizer 2016 batteries, a more conservative guesstimate would be 1h with real-world battery behaviour and offbrand batteries.

by the way, 20x 2016 coincells are only $3.88 shipped at dealextreme.

energy dissipation of the whole thing would be about 0.75W

but I'd really have to run tests to confirm this... the samsung led datasheet is quite vague about brightness and max power consumption (e.g. they state brightness at 60mA, but half a page above they say that max allowable current is 30mA)


another point: what about chaining all 4 leds and 4 batteries in series to even out Vf differences? anybody got experience with that?


edit:
to put it into perspective with the chimera:
chimera: ~$350, charging circuits, cree led, I guess >100 lumen output Actually, its about 300-400 lumens. :nana:
cclight: $20 max, single-use cr2016 batteries, not the most efficient leds, no idea about output, 10 lumen would be great already

I fixed it

 

[Sabrewolf]

spencer: kinda overlooked that.... ~50 lumen would be quite bright for such a tiny light

Mosser: do you meat that one: http://www.iainsinclair.com/products/eonclassicintro.html ?
It seems to be 2 or 2.5mm thick at the thinnest point... it's more like 7mm at the thickest point (I guess they use a 5mm led, which has a 5.8mm diam max. then you still need two plastic shells)


One problem that still exists is the switch... I don't know if Farnell even ships to individuals. And the switch is extremely tiny, and momentarily only.

A pressure switch like the sinclair and many cheapo pocket flashlights use is also not an option. Guess what would happen if this light sits in my wallet in my back pocket...

Anybody got an idea for the switch? A switch where you close the contact with your finger would be an idea. But that would need an smd transistor - fingers have to high a resistance to power 4 high power smd leds

You could use a simple mosfet circuit. Then you still keep your momentary switch to turn it on/off :twothumbs

 

[balou]

LouRoy: overlooked your post... I once had exactly such a light. 5mm LED, 3x LR44 batteries, about 6-7mm thick. Way to fat.... and it started to fail after just a few uses.

Sabrewolf: 100 < 300-400 lumens. Nothing wrong about my post
Oh, and do you know a place where to get sub-2mm lipoly batteries?
About the MOSFET circuit: only thing that comes to my mind would be a flipflop, and building one in CMOS yourself would probably take more space than available. Or do you mean flipflop plus mosfet transistor?

Such a circuit would solve the momentarily-on problem.. but a bigger problem would in my opinion be the finicky smd switch. Hard to get, easy to break off.

So... an alternative would be a pattern on the circuit board like this:
http://www.maxtechcircuit.com/files/Products/RubberMembrane/Rubber-CarbonTactileKey2.jpg
You close the contact with your finger, and then it either actuates a MOSFET directly, or is preamplified with a BJT (but MOSFETs should probably need a rather small current, so hopefully a BJT is not needed). Because, IF I gonna include semiconductors in the whole thing, I could as well use some more to replace moving parts.

Edit: but SMD parts would again mean that I have to order from an electronics supplier. Farnell seems to be my best choice - shipping costs from digikey to switzerland are 60$

 

[spc]

didn't polaroid make a thin disposable led light a while ago?

 

[Sabrewolf]

didn't polaroid make a thin disposable led light a while ago?

Yes, it used the battery that was builtin to the Instant-film cartidges.
After you used the cartidge in the camera, you just shoved it in the
flat light of thiers and used the battery up.

 

[LouRoy]

do you think that such a thin light is a stupid idea?

No, I think it is a great idea. The ultimate EDC. When can I send paypal??? :thumbsup:

 

[snarfer]

Farnell seems to be my best choice - shipping costs from digikey to switzerland are 60$

I have this same problem with shipping costs from Digikey, in my case to Thailand.

I spoke to a representative there a while back and he told me that on request they could ship via the US postal service. Much cheaper.

I never tried it because I found an even cheaper way - having a friend receive the order in the US and repackage it, which also saves me on customs fees.

Oh almost forgot. Mouser has much lower international shipping fees. So that could also be an option. Farnell tends to have really inflated prices for some reason.

 

[balou]

Sabrewolf: What MOSFET circuit did you mean exactly?

snarfer: Yes, already did that once with letting somebody else buy the stuff and send it to me. Was over at headfi... a bunch of opamps Will definitely try to piggyback on some other order if possible.


General question: What light output?
50 lumen seems to be a big bright. Especially if you consider the small batteries. I mean, the Fenix E01 has just 10 Lumen. This light would compete with the Photon, Fauxton and the smallest keychain lights, up to maybe the Fenix E01.

Crazy high output or reasonable battery runtime?
A compromise would be 2 LEDs.


Btw, there's space for 6 CR2016 on a credit card. That would be 3v, 540mAh, about the same power as one AAA battery. So if the E01 with all the regulation loss can put out 10 lumen 10h longs... then 20-25 lumen 5h would be not bad.


edit: seems I just contradicted myself somehow . Yes, the light's small, but 6x 2016 provide quite a bit of power, only realised that when writing the last sentence. here's the layout as of now. anybody got a suggestion if I should drive the 2 leds with 2x3 or 3x3 volt? 3v per led might be a bit to dim. BUt - under which condition does this led emit 13.5 lumen as stated on the link above?

 

[spencer]

I would say that each LED emits 13.5 lumen when each die is driven at 20mA. There are three dies per LED and all are individually addressable kinda like the MC-E.