OT: uCalc Processor



#2

For those not interested in credit card calc design, please tune out now.

Working on my uCalc project and am still stuck on what processor to use.

I was all set to have a big fat 512K/32K+ PIC32 in there (layout half done already), but realised I ultimately won't be happy with the battery life. 2 months at best stand-by from a single CR1620 cell.

The AT91SAM7L128 as used on the new HP platforms is an option, but it's only 128K/6K (less SRAM than the uWatch), and requires an external RTCC, and it's not cheap.
Could gets years standby out of that option though.

The 64KB/8KB PIC24FJ64GA104 is looking good. It's cheap, got an RTCC, and is the same as used in the uWatch. It's an XLP chip, so standby power would be the shelf life of the battery. Only problem is the current uWatch firmware already maxes out this chip, and the uCalc will need bitmap fonts for the 132x32 display.

The MSP430F5437 has 256KB/16KB, RTC, and around 3 years standby.

Other options looks fairly miserable.

I guess it comes down to what's most valuable, computing power or standby battery life?

Battery life for continuous operation is looking to be around several hundred hours.

(No, rechargable and/or solar is a miserable option IMO)

Opinions?

Dave.

Edited: 8 Dec 2009, 1:37 a.m.


#3

I'd vote for battery life.

HTH

#4

How about a PIC with more memory like the PIC24FJ128GA106, it's 128KB/16KB. According to the spec with the RTCC running it's only draws 7uA -- 10 times more than the XLP -- but that's still more than a year of power down clocking with a CR1620. How many i/o pins do you need for your design?

-Katie


Edited: 8 Dec 2009, 2:46 a.m.


#5

Typical is under 4uA for that part which isn't that bad actually.

Don't need that many I/O, a 44pin job will do nicely.

But silly me just realised an obvious way I can have my cake (PIC32) and eat it too (shelf life), just needs some more parts...

Dave.


#6

Just connect an external car battery? ;)

#7

Otherwise the MSP430 seems like a reasonable compromise.

#8

My option is the MSP430 version (I like them very much) and they can use BCD math directly (IIRC)

Best regards

Nelson

#9

Nope, not an oxymoron. check out Energy Micro at EnergyMicro.com and see if their low-power story tickles your engineering bone. Don't know the costs. Flash currently limited to 128K but they've got big plans.

-Steve-


#10

Quote:
Nope, not an oxymoron. check out Energy Micro at EnergyMicro.com and see if their low-power story tickles your engineering bone. Don't know the costs. Flash currently limited to 128K but they've got big plans.

Cute video.

They are starting out right being on Digikey, but no parts yet...

If I can buy the demo board with a part on it, why can't I buy the parts?

Perhaps explains why the datsheet is Rev 0.82

Dave.


#11

Yep, they're very, very new. Growing pains.

- Steve -


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