Using Lithium Ion Battery Packs instead of AAs

So I'm trying to mod/hack an embedded sensor system out of wiimote and wiimotionplus bits. One the things that will have the biggest impact on size is switching from AAs to a li-ion battery like this:

Now 2 x AA (which is what is in a wiimote) should be 3v. I've read that the rechargeable ones can have as much as 1.9v each, so that would be 3.6v.

Those sparkfun batteries are rated at 3.7v. I'm guessing the wiimotes have power regulation built-in, so is 3.7v be a safe voltage to throw at it?

Next thing is mAh. The sensor would be powering a wiimote and a wiimotionplus for no more than an hour at a time, so massive battery life isn't a big deal. I just have to make sure to charge them before every use. But what would the mAh rating be for off the shelf 2 x AAs?

Since it's going to be for an embedded system, smaller is better. It's all going to be worked into a wristband type thing.

The choices for smaller batteries seems to be this 110mAh one that's very small/light:

The next one up is 900mAh:

It's over twice the size and over 6 times heavier. I'd want to go with the 110mAh, but is that too little to power a wiimote/motionplus for a reasonable amount of time (a couple hours maybe).

You can find mAH ratings for AA batteries online. Last I looked they were like 1200 or 1500mAH for Alakaline batteries. 2 in series woulfd be 3V @ 1200-1500mAH.
I have a 1000mAH LiPO built into an RF remote. It has measured 4.1V when fully charged. It is pretty darn light.
I use a MAX1811 chip to control charging it from a 5V source.

I don’t know what the wiimote have for voltage control. We use 2 AAs in ours, or 2 NiMH batteries - I think the base they plug into takes care of charging them.
Haven’t tried opening one to see what’s in it.

And take a look here!

more battery types than I even knew existed!
Saw some that are listed as 45V even - that'll get that wiimote rumbling in your hands!

Do mAH work like they seem? A 120mAh would last a tenth s long as a 1200mAh?
How long do your batteries last in your wiimote? I've never owned one for actual gaming with (no nintento wii), so I've not used it for more than 10-15min at a time messing around with max/msp and stuff.

I plan on ordering the 5v/usb lipoly charger from sparkfun too (might even embed that into the whole thing as the small one is just that, really small. And I think leaving access for a microusb port vs leaving access for removing the battery and clip, would allow it to be more compact.

I busted open my minimote (25% smaller) but everything is pretty tiny so I can't tell what's what.

CrossRoads:
You can find mAH ratings for AA batteries online. Last I looked they were like 1200 or 1500mAH for Alakaline batteries. 2 in series woulfd be 3V @ 1200-1500mAH.
I have a 1000mAH LiPO built into an RF remote. It has measured 4.1V when fully charged. It is pretty darn light.
I use a MAX1811 chip to control charging it from a 5V source.

I don't know what the wiimote have for voltage control. We use 2 AAs in ours, or 2 NiMH batteries - I think the base they plug into takes care of charging them.
Haven't tried opening one to see what's in it.

Yes, 120mAH is 1/10 of 1200mAH.
My wife & son play for hours on a charge. I don't play, never got into sitting there twiddling my thumbs staring at the TV or poking buttons staring at a little screen. They both play gameboy, etc. Give me a decent PC game with a joystick, that's more my style.

Yeah I'm the same way, never got into the 'wii' idea of gaming. I feel better about touch based interfaces (iOS) as it's somewhat tactile, but a nice joystick is hard to beat.

kriista:
Yeah I'm the same way, never got into the 'wii' idea of gaming. I feel better about touch based interfaces (iOS) as it's somewhat tactile, but a nice joystick is hard to beat.

A problem with 3D interfaces on current systems is, in a way, the opposite problem of trying to use a mouse to control a 3D GUI; you are trying to navigate what is a 2D interface (2D as in the screen, not the rendering method) using a 3D controller. What is needed is a 3D display. I'm not talking about a "3D window", which is what you would get if you simply added a 3D TV or something similar.

What is needed is a 3D immersive experience.

So far, you can only get that in one of two ways: A high-resolution, wide field-of-view (FOV) HMD - or a high-resolution six-surface CAVE (Cave automatic virtual environment - Wikipedia).

Of the two, you are likely to see the first come into fruition before the latter (though one could argue that a large enough single-wall 3D projector system could give some semblance). Its one of cost, mainly.

When you use a 3D controller in a full-immersion setting like you get with a quality HMD (which currently aren't cheap - Vusix HMDs are nice, but they are not "full immersion" - Rockwell/Kaiser ElectroOptics on the other hand - drool), it become natural. We have inexpensive 3D controllers now, all we need is the inexpensive, wide FOV HMD to complete it.

Of course, the only issue at that point becomes one of avoiding injuries while using such a platform (especially if multiple people are playing); that's probably not an easy problem to solve (some of it could be done in software - at least warning the players after mapping the real environment using something like the Kinect).

:slight_smile:

I’d rather go with real 3D - no games, do the real thing.
Fly a plane. Play ice hockey. Fence!

I checked this page to see if they had anything between 120 and 900 but it doesn't seem they go that low at all.

What I'll probably do is order two of each to test. The 120 would be ideal as it's tiny and weighs nothing, but if the charge doesn't last over an hour, then I'll need to use the bigger ones. Either way I'm sure I'll find a usage for them at some point (wether I use small or large).

I did some googling for Wiimote battery life but it was mostly in the "hours" range with nothing more specific. Is there a spec to look at on a wiimote that one can do the math for and find out how long a 120mAh battery would last on it?

Next I have to consider wether I'll do an embedded charger (using that tiny board) or make the battery removable.

CrossRoads:
And take a look here!
http://batteries.batterymart.com/search/index
more battery types than I even knew existed!
Saw some that are listed as 45V even - that'll get that wiimote rumbling in your hands!

Actually, can I attach a JST jumper to the battery (and circuit) so the other end of the jumper is reachable via an opening in the wristband, can I charge it that way? Or does circuit need to be removed in order to charge it?

Depends on the battery & charger you select.
The MAX1811 can be built in and turns on as needed.
I used it thusly in an RF remote control.
Runs off battery, uses USB to charge the battery. Or runs from USB if battery is not present.
(did testing with 3 AAs, runs now on 3.7V LiPo)

Try this one

They are very small!
This is a 1000mAH I got from www.gravitech.us. $12. Have to ask for it, not sure they have it listed on their website: LiPo-1000.

This one could be even smaller, 500 mAH http://www.batterymart.com/p-batt-2682-atlinks-5-2682-battery.html

I was planning on using this charger:

As it seems small enough to just embed in the project.

At first I was going to use this, but it looks the same, only bigger (and mini usb instead of micro usb):

These both have the chip your talking about right? That’s good on how it works. I was worried that it would fry the wiimote by sending it 7V+.

Those medium ones look nice, but I plan on ordering stuff from sparkfun anyways (the mini batteries to test it out, charger, etc…)

Not the same chip, but something similar.
If you not comfortable building up a design from scratch that certainly seems like a feasibile solution.
Be aware that it puts out 4.2V during charging.

I guess it's a moot point if the circuit is off while charging (as it would be in my case).

So you will have a swith that will disconnect the power then?

There’s a power button for the wii no? It’s been a while since I use it, but I remember it going dead if you wanted it to, at which point you could stick a 500v battery in there as there is no circuit connected right?

There is not a switch that disconnects the battery - they just go into a kind of sleep mode that is still seeing the battery voltage. There is not a mechanical switch the totally disconnects the battery.