For those playing along at home, some preliminary uWatch MK2 specs that looks very do-able on the surface:

50mm x 40mm x 16mm

Fully enclosed case, no protrusions.
128 x 64 dot matrix display with white LED backlight:

http://www.newhavendisplay.com/index.php?main_page=product_info&cPath=21_96&products_id=2072

Visible area is quite mall though, only 26mm x 16mm.

Watch band would have no attachment, i.e. velcro completely through holes in the case, nothing to break.

16 key tactile dome keypad minimum, probably 20.

Possibly a micro trackball and/or scroll switches (WOW factor).

Rechagable NiMH battery, life probably around several hundred hours continuous display.

USB interface allows comms and charging. Firmware upgrade via USB would be nice, but might be processor dependent.

Perhaps an IR LED, and another expansion port.

Processor choice is open, but more powerful than the PIC24F. Maybe 512K flash and 32KB or 64KB SRAM. 32bit ARM probably a good choice.

It could be made smaller with a different battery choice, but I'm thinking single AAA is cheap and simple.

Only custom bit would be the case, but I think that should be pretty simple.

Sound like a dream come true?, bad idea?, something else entirely?

Dave.

Just my $ 0.02

AAA battery or similar is a GOOD idea. Non-standard batteries (I mean "non easily available") are a real pain, specially if soldered. When aging reduces charge capacity, you end with a pile of nice devices that you cannot use anymore. And the replacement batteries are no longer manufactured.

Using a uWatch implies some soldering skills on the owner's side, but I still prefer a standard battery.

Eventually, the "pair of CR2032 approach" may be acceptable.

Congratulations for your fine design and also for the EEVlog.

Andrés (not a uWatch owner yet, but... )

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Sound like a dream come true?, bad idea?, something else entirely?

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Not sure if it is quite a dream come true, but certainly not a bad idea.

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Yeah, lets just say a tad bit better than the current one! :->

Dave.

Make that about 48mm x 40mm x 14mm

Now I've gotta do is find a place that makes membrane keypads protos cheaply. There are ways to DIY but probably won't look as good.

Dave.

20 keys would definitely be much better than 16. Even 24 if you can cram them in.

I'd recommend the PIC32 (MIPS) or various Atmel AT91SAM family ARM parts. Power consumption will definitely be higher than for the PIC24, though.

I've been told that essentially all of the companies that make membrane keyboards do it for fairly low NRE. However, those usually don't have domes, so I'm not sure whether that adds a lot to the NRE.

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20 keys would definitely be much better than 16. Even 24 if you can cram them in.

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Yep, will all depend on the final size of each button.

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I'd recommend the PIC32 (MIPS) or various Atmel AT91SAM family ARM parts. Power consumption will definitely be higher than for the PIC24, though.

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Yes, both of those would be my first initial pick.

Power consumption isn't much of an issue given that the unit is rechargable, and most of the time it will operate at say 32KHz running and displaying a clock.

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I've been told that essentially all of the companies that make membrane keyboards do it for fairly low NRE. However, those usually don't have domes, so I'm not sure whether that adds a lot to the NRE.

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I've got two ways I can do the front panel. Either domes directly stuck onto the front panel PCB and silkscreen labeling (cheaper DIY solution). Or a proper stick-on membrane front panel. The membrane has the advantage of looking more professional, and having the text directly over the button thus potentially reducing the button spacing (more buttons). But the membrane has the NRE and I'd have to come up with a proper graphical design template (not my area of expertise)

The advantage of this new uWatch2 idea is that the LCD is inside the case, so the membrane keys can come right up to the display window giving much more room for the keypad. And you can protect the LCD with some glass or polycarb sheeting. Should be fairly water resistant too.

Dave.

Why NiMH rather than lithium polymer? They have higher energy density, partly because they don't require a metal jacket. They require careful control of charging, but just about all of the fancy USB power control/regulator/battery charger chips (e.g. Linear Tech LTC3455, LTC4088) are designed for lithium cells, while most of them don't support NiMH. Lithium polymer cells don't have the safety problems that have plagued lithium ion batteries.

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Why NiMH rather than lithium polymer? They have higher energy density, partly because they don't require a metal jacket. They require careful control of charging, but just about all of the fancy USB power control/regulator/battery charger chips (e.g. Linear Tech LTC3455, LTC4088) are designed for lithium cells, while most of them don't support NiMH. Lithium polymer cells don't have the safety problems that have plagued lithium ion batteries.

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Cheap and easy to replace, and standard size available from any electronics store (people like that sort of thing).

Plenty of battery charger chips in usable packages available, and oodles of single cell DC-DC converter options. I don't need to use an integrated charger/DC-DC chip.

I'm open to suggestions though, might have a look, got some links?

Dave.

Actually, looks like it may have to be Lithium Polymer.

I've found a perfect size off-the-shelf case (50mm x 35mm x 15mm), but it won't fit a AAA or AAAA along with either of the specified LCD's. Once I get LCD samples there is a slight possibility I could squeeze in a AAAA and the 128x32 display, but it's a bit ugly. What a shame, I would liked to have used a standard battery :(

The LP452030P6H from HERE looks almost ideal. 200mAh @ 3.7V

The final watch thickness will depend upon whether I use the supplied case lid or roll my own. If I roll my own the thickness could be as small as 13mm, which is quite amazing really as that's the same as my standard Timex watch. But 15mm is probably more achievable.

This is all starting to really come together now. The hardware part looks to be the membrane keypad.

This is quite exciting! (again)

Dave.

Edited: 18 Apr 2009, 12:41 a.m.

Dave;
Are quad A cells common in Ausland? The only place we see AAAAs in the states are inside 9v batteries or on 12 year old Chinese Olympic gymnasts.
Those Li-Poly batteries look too good to be true, except for the picky charging system. They may be worth the trade off though.
I guess i have to start saving my new toy money again. - db

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Dave;
Are quad A cells common in Ausland? The only place we see AAAAs in the states are inside 9v batteries or on 12 year old Chinese Olympic gymnasts.

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No different here!

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Those Li-Poly batteries look too good to be true, except for the picky charging system. They may be worth the trade off though.

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Looks like I don't have any choice if I want to use an off-the-shelf case.

If I used a bigger custom case I could use a single AAA, but the watch would be bigger and there is that NRE and design work to contend with.

This way it's cheap and simple to get a good looking proto for minimum cost, just drill out the holes for the USB and watch band connectors. For production I can order the boxes with holes pre-drilled.

Dave.

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I've found a perfect size off-the-shelf case (50mm x 35mm x 15mm)

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Maybe I missed something, but you're still talking about a watch, aren't you? Or are you going to transit into the realm of true pocket calcs ;-)

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No, as I stated in another recent thread I think that would be a complete waste of time and effort. Not to mention boring and un-cool.

Unless you call a 50mm x 35mm x <15mm calc with 24 keys a pocket calc? I can leave the watch band holes out for those who want to slip it into their fob pocket.

Dave.

I now have LCD's and cases in my hot little hands.

Unfortunately the LCD wasn't able to be used the way I wanted it, so that means a lot less space in the case than hoped for.

This means a MUCH smaller battery, only 70mAh, but this should still give a reasonable life when just displaying the time/date or operating at minimal speed.

It looks like I can still fit everything into 50mm x 35mm x 12.8mm which will be amazing if it all comes together.

Forget the trackball though, but amazingly there might be room for a micro SD card slot too.

The super tiny Lithium Polymer battery is on it's way.

Creating your own calculator is FUN!

Pray for no show-stoppers.

Dave.

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Pray for no show-stoppers.

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