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

[Dave Taht <dave.taht@gmail.com>]

jeeze guys, all I asked for was an estimate as to the change to the BOM.
Could be a Macx-2, might not be worthwhile at all.

My concern was that there are 6+ short power flickers a day - forcing
a reboot - in places like Nicaragua. These events are *interesting*
from a network analysis perspective, as flickers like this cause
massive network disturbances.

I don't care about battery life longer than about 30 seconds, although
a case could be made for 24 hours. Just wanted the analysis of what it
would really take, given how little power this thing sucks...

and I hate ANYTHING that needs a user-replaceable component, 5 years
after manufacture. So I'd prefer the actual analysis based on power
draw, etc, before
making any decisions.


On Wed, May 9, 2012 at 11:21 AM, tz <thomas@mich.com> wrote:
> 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@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@gmail.com> wrote:
>>>
>>> On Wed, May 9, 2012 at 9:47 AM, Eric S. Raymond <esr@thyrsus.com> wrote:
>>> > Dave Taht <dave.taht@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@lists.bufferbloat.net
>>> https://lists.bufferbloat.net/listinfo/thumbgps-devel
>>
>>
>>
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>>
>>
>> --
>>
>> (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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-- 
Dave Täht
SKYPE: davetaht
US Tel: 1-239-829-5608
http://www.bufferbloat.net