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

[Ron Frazier (NTP)]

Dave Taht <dave.taht at gmail.com> wrote:

>On Wed, May 9, 2012 at 1:58 PM, Ron Frazier (NTP)
><timekeepingntplist at techstarship.com> wrote:
>> I'm just an interested third party.  You guys are running the show.
> Use the
>> ideas as you see fit.  Just give me some credit if you end up using
>my
>> ideas.
>
>absolutely. Got another fictional character you resemble?

You're not confusing me with esr are you?  I like all captains of starships named enterprise, but I don't know if I resemble any of them.

Sincerely,

Ron

>
>And I'm totally into discussing this stuff, later, but right now I'm
>too busy with codel....
>
>>
>> Sincerely,
>>
>> Ron
>>
>>
>>
>> On 5/9/2012 4:46 PM, Dave Taht wrote:
>>>
>>> A lot of that stuff I'd want to reserve for the Macx-2. Can I keep
>our
>>> request of navisys limited to merely the supercap and silkscreen?
>>>
>>> On Wed, May 9, 2012 at 1:41 PM, Ron Frazier (NTP)
>>> <timekeepingntplist at techstarship.com>  wrote:
>>>
>>>>
>>>> Hi guys,
>>>>
>>>> I do see the point TZ was making about the problems of increasing
>the
>>>> design
>>>> and production costs.  However, if the supercap turned out to be
>>>> potentially
>>>> feasible, I have some Circuit Cellar magazines and such that I
>could
>>>> rummage
>>>> through for info on micro power conversion components.  I know they
>>>> exist.
>>>>  I have no idea about specs and efficiency.  How much amperage and
>at
>>>> what
>>>> voltage is the unit expected to draw if disconnected from the USB
>power
>>>> source?  Is it expected to continue tracking?  I assume this will
>change
>>>> if
>>>> an external antenna is attached.  How long should it be maintained?
>>>>
>>>>  From a user perspective, I'd recommend the following features, if
>you
>>>> have a
>>>> viable choice:
>>>>
>>>> * Hi sensitivity internal antenna / chipset that can be used
>indoors in a
>>>> residential type structure.
>>>> * External antenna port in case you're in a steel building or
>basement or
>>>> something with no signal.  Use commonly available, generic,
>possibly
>>>> powered, antennas.
>>>> * GPS status led.  (My BU-353 slowly flashes when it has a fix,
>shows
>>>> steady
>>>> with power but no fix.)  The led should be synchronized to the pps.
>>>> * Supercap preferably, or battery which is easily user replaceable
>and a
>>>> common part number, such as CR2032 for example.  That battery may
>be too
>>>> big, but you want something readily available.
>>>> * If a battery is involved, a small flashing led to indicate a weak
>>>> battery
>>>> alert, kind of like what is on a smoke alarm.
>>>> * My BU-353 has a magnetic base.  Something like that might be
>useful for
>>>> positioning the antenna.
>>>> * May or may not be relevant, but, would 5 - 10 Hz position sensing
>>>> improve
>>>> accuracy and stability for your purposes?
>>>> * You may wish to expose the pps signal on a screw terminal or
>connector
>>>> in
>>>> case you want to attach other instrumentation to that signal.
>>>>
>>>> Here's a possible alternative to providing an external antenna
>port, and
>>>> all
>>>> the hassles of piping RF around.  With my BU-353, the "puck" device
>>>> contains
>>>> both the electronics and the antenna.  The only cord coming from it
>is
>>>> the
>>>> USB cable.  So, it might be preferable to have a sealed weather
>proof
>>>> unit,
>>>> and just use extension cords for USB rather than extending the RF
>>>> section.
>>>>  I know you can easily extend USB 10 feet or so.  I think you can
>go much
>>>> further with powered hubs and such.  Just a thought.
>>>>
>>>> Here's a wild idea, maybe not practical, but, you could attach a
>solar
>>>> cell
>>>> to the external antenna and / or the thumb-gps case.  This could
>feed
>>>> power
>>>> back to the GPS board and prolong the life of the battery or slow
>the
>>>> drain
>>>> of the supercap while powering the antenna if the antenna is in the
>sun.
>>>>  You could even draw some energy from ambient indoor lighting.  I
>have a
>>>> solar powered "atomic" watch from Casio that does this.  It never
>needs a
>>>> battery, never needs charging, and never needs setting.  Very
>handy.  I
>>>> also
>>>> have two "atomic" wall clocks that do the same thing.  I think they
>use a
>>>> rechargeable battery instead of a supercap.
>>>>
>>>> Here's another idea, which may or may not have already been
>discussed.
>>>>  Do
>>>> you want to have an on board RTC, which can keep outputting valid
>time
>>>> for a
>>>> while, if the satellites are not available due to weather, jamming,
>>>> interference, etc.?
>>>>
>>>> Sincerely,
>>>>
>>>> Ron
>>>>
>>>>
>>>>
>>>>
>>>> On 5/9/2012 2:35 PM, Dave Taht wrote:
>>>>
>>>>>
>>>>> 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 at 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 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
>>>>>>>>
>>>>>>>>
>>
>>
>>
>> --
>>
>> (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
>>
>
>
>
>-- 
>Dave Täht
>SKYPE: davetaht
>US Tel: 1-239-829-5608
>http://www.bufferbloat.net


--

Sent from my Android Acer A500 tablet with bluetooth keyboard and K-9 Mail.
Please excuse my potential brevity.

(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 email messages very quickly.  If you need a reply and
haven't heard from me in 1 - 2 weeks, send your message again.)

Ron Frazier
timekeepingdude AT techstarship.com