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

[Dave Taht]

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?

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