[chych]

Does anyone know how to charge Li-Poly batteries/know of a schematic for a charger for this? We need some thin batteries for a project and Li-Poly seem to be the best choice as it can be thin.

On another note, does anyone know of any thin Ni-MH or Li-Ion batteries with a 1.5"x1.5" surface? (about that).

 

[tangent]

Li-Ion is pretty picky in terms of the charging regimen it expects. You should use a charge controller for this. Lots and lots of companies make such things. My short list for finding a suitable one would be Maxim, On Semiconductor, Linear Technology, and National Semiconductor in no particular order. There are probably other companies making suitable products. You could also do a search at the parts distributors to see what you can actually get -- that may inform your choice greatly.

Regarding flat batteries, NiMH wants to use cylindrical cells. To get a flat surface like in a NiMH 9V, you end up with several cylindrical cells packed into the thing with lots of wasted space in there. Li-Ion is able to give you truly flat cells, so I wouldn't look elsewhere.

 

[aos]

Your biggest trouble will be getting actual batteries. For some unknown reason they are not available in standard packages. So connecting a battery to your device will be a nightmare as there is no way to buy a battery holder for a specific battery you need and your only option might be to solder wires to its terminals.

 

[chych]

I'm sure we can whip something up to connect the batteries, use molex connectors or something. The battery I've found is:

http://www.ulbi.com/product-display.asp?ID=47

Very thin, seems like a very good battery for our project.

Anyways, What we're doing is making a small mp3 player with an LCD screen and touch sensing buttons (sounds like something else on the market *cough* ipod), but based around a CF card, so it's really small (and a laptop hard drive later, once we figure out the file system).

Also I believe we will use a charging system from maxim, so that will be set. We are also aiming to charge it off USB, though that will probably not give enough power.

Now unfortunately the other guys in my group aren't audiophiles, so sticking a nice headamp won't be easy

Actually, are there any designs for some decent headphone amps that take a very small amount of space?

 

[tangent]

Quote:

For some unknown reason they are not available in standard packages.

Li-Ion cells are roughly 3V each, so if they were available in AA packaging, you just know some idiot would stick a pair into his Walkman and fry the thing, then sue the manufacturer. By intentionally choosing nonstandard sizes, they avoid this problem.

Quote:

are there any designs for some decent headphone amps that take a very small amount of space?

MINT?

 

[chych]

Quote:

Originally posted by tangent MINT?

Ack, the MINT is about the size of the finished product

I think your 'micro cmoy' is close to the size I want, but still probably too big. Hmm I'll have to see.

 

[tangent]

Do you want good sound or small size? Pick one. If super-small size is that important, you can get a headphone amp on a single surface mount chip. Hook up power and you're ready to go.

If you want good sound, you'll need to add buffers, and you'll need to use regular op-amps which also drags in lots of resistors.

The MINT board is scarcely larger than the surface area of a CF card, and you could cut it down by using a digital volume control, going with surface mount resistors, eliminating the input caps, and skimping on the power caps.

 

[Smonkey]

Be careful charging lith-polys, they can cause violent fires when overcharged.

here's a link to a test done deliberately over charging them:

http://www.rcstuff.us/battery/lipo/LipoFire.wmv

-Tom

 

[Voodoochile]

Bad location for that meter!
Too funny.

 

[Chipko]

Good news is you can pick up a cheap smoke detector for the overcharge detection

 

[10SNE1]

Quote:

are there any designs for some decent headphone amps that take a very small amount of space?

Xin Feng, AKA 'Fixup' is the king of microminiaturizing Jung multiloop amps.

He usually posts at Headwize forums and his website www.fixup.net has info on his tiny amps which are now pure SMD.

I believe he also has a MP3 project underway similar to yours.

 

[tangent]

Well, we're halfway there.... Tadiran Batteries makes primary lithium batteries in standard sizes. They would be good for low-power amps. They're available in DIY quantities, but they're awfully expensive.... Digi-Key wants $5.50 per AA size cell for the standard type.

I wouldn't mind paying that price if they were rechargeable....