[Thumbgps-devel] Article -- Macx-1: GPS receiver with standard USB connector and PPS support

[tz]

It doesn't work that way.  Microampere DC-DC converters?  That isn't a
swap, it is a redesign, if microamp converters are possible - the base
losses are high so you won't hit a high efficiency.  You get high
efficiencies when dealing with lots of amps.  For it to last overnight you
would need a very large (physically) cap.

There would be no booting problem.  It would merely lose the real-time
clock and/or location backup so would take a bit longer starting.

The battery (or cap) only kicks in when the power goes away and is only
needed to make the startup faster, e.g. cycling power on the computer or
router.  USB should be constantly providing 5V 99.9% of the time.

I could argue that if surviving only a short power disconnect is ok, then a
supercap might be better, but then it is probably a large engineering
change since the caps and batteries usually have vastly different
footprints.

Good batteries can last decades - even Supercaps have a finite lifetime.
It is a matter of cost, both in redesign, size, and reliability.  But do
you want to add $5-$10 to the cost of the unit to make a cheap ($30-$50)
GPS last over a decade?  Buy a second, seal it hermetically, and put it in
your freezer.

If you want to add a few thousand in NRE costs, there are a lot of other
things I would redesign.  Use a USB 2.0 chip to get 125uS jitter.  Allow
for a detachable or external antenna (which can be run to the window).
Find a more optimal chipset.  Maybe a coin-cell port so the battery can be
replaceable.  But the point was to be as cheap as possible so in this case
it is adding one wire.

You can always break yours open and if you can find a supercap with the
specs (Sparkfun has a 3.3v available, but don't put more than 3.3v on it),
you can swap the part.

On Wed, May 9, 2012 at 1:50 PM, Ron Frazier (NTP) <
timekeepingntplist at techstarship.com> wrote:

> **
> Hi all,
>
> (I'm copying this only to the thumb-gps list and to TZ, the most recent
> commenter, as I don't know all the parties in the header of TZ's message.
> You guys can forward it to whomever else may need to see it.)
>
> Speaking strictly as a potential user of the thumb-gps device and amateur
> interested party, I would rather see a supercap, if feasible.  I hate the
> idea of devices having batteries that I have to worry about failing in 5-10
> years.  I've had the cmos batteries fail in a few computers, sometimes
> preventing them from booting.  It can get really ugly trying to revive
> them  A good high efficiency dc-dc converter chip should allow you to drain
> all but the last bit of energy from the cap while maintaining whatever
> working voltage you need.  I cannot speak to size issues, as I have never
> designed a circuit board with one.  The GlobalSat BU-353 that I have has a
> supercap, I believe.  Exact backup time is not stated, but I believe it's a
> few days.
>
> Sincerely,
>
> Ron
>
>
> On 5/9/2012 1:12 PM, tz wrote:
>
> For a given size (and circuit board footprint) a supercap will have much
> less capacity and it has an exponential voltage decay curve, so it might
> have plenty of charge but not at a voltage that will hold the data.  This
> usually means hours, not days of backup.
>
> A good rechargeable lithium will last several years, maybe longer as there
> will be no charge/discharge, maintains voltage until it is nearly
> exhausted, and can hold the data for days or weeks.
>
> On Wed, May 9, 2012 at 12:55 PM, Dave Taht <dave.taht at gmail.com> wrote:
>
>> On Wed, May 9, 2012 at 9:47 AM, Eric S. Raymond <esr at thyrsus.com> wrote:
>> > Dave Taht <dave.taht at gmail.com>:
>> >> What would be the change in cost and delay in manufacturing to switch
>> to
>> >> using a supercap, rather than battery?
>> >
>> > Why would a supercap be better?
>>
>>  Effective lifetime of... forever. no need for replacement. insanely
>> fast recharge. smaller (probably). What's not to like?
>>
>> I am not in a huge hurry to get into manufacturing, and I merely
>> wanted to cost out what what it would do to the bom, any changes to
>> the PCB, and get an estimate for the time it would take to do. I think
>> it will bump the unit cost up slightly,
>> but what price, forever?
>>
>> > --
>> >                <a href="http://www.catb.org/~esr/">Eric S. Raymond</a>
>>
>>
>>
>>  --
>> Dave Täht
>> SKYPE: davetaht
>> US Tel: 1-239-829-5608
>> http://www.bufferbloat.net
>>  _______________________________________________
>> Thumbgps-devel mailing list
>> Thumbgps-devel at lists.bufferbloat.net
>> https://lists.bufferbloat.net/listinfo/thumbgps-devel
>>
>
>
> _______________________________________________
> Thumbgps-devel mailing listThumbgps-devel at lists.bufferbloat.nethttps://lists.bufferbloat.net/listinfo/thumbgps-devel
>
>
> --
>
> (To whom it may concern.  My email address has changed.  Replying to former
> messages prior to 03/31/12 with my personal address will go to the wrong
> address.  Please send all personal correspondence to the new address.)
>
> (PS - If you email me and don't get a quick response, don't be concerned.
> I get about 300 emails per day from alternate energy mailing lists and
> such.  I don't always see new messages very quickly.  If you need a
> reply and have not heard from me in 1 - 2 weeks, send your message again.)
>
> Ron Frazier
> timekeepingdude AT techstarship.com
>
>
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