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Evil Uncle Chris
Guest
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 Posted:
Thu Nov 24, 2005 12:50 am Post subject:
Wired GPS recommendation for PDA TomTom 3? |
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I'm using a Dell Axim X30 PDA, with a TomTom windscreen mounted cradle.
I have a cheap wired GPS unit which plugs into the right hand side of the
cradle, connecting it to the PDA, and supplying the GPS with power via the
same cable.
I am getting a bit fed up with the GPS not finding any satellites on very
cold mornings, having to use POL PDA tester software to reboot the GPS after
I have left the car parked under cover, such as in a multi story car park,
and general slow updating at roundabouts and junctions. I am guessing that
one of the newer SIRF Star III receivers would be better? I leave the GPS in
the car all the time, and keeping a BT GPS charged would be a disaster for
me..so, any recommendations, for the unit and retailer?
I have been briefly looking at the Holux GR-213 G-Mouse, on eBay for about
£50 UK, and £70 internet retailers. Happy to spend a bit more if it's worth
it.
Thanks for any advice
Chris |
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davidsteward4@yahoo.com
Guest
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| Posted:
Thu Nov 24, 2005 1:08 am Post subject:
Re: Wired GPS recommendation for PDA TomTom 3? |
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I have just replaced a Garmin GPS 35 with a TOMTOM receiver from eBay
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=5831769767&rd=1&sspagename=STRK%3AMEAFB%3AIT&rd=1.
I cost just over £50 inc. delivery. The Garmin failed after what I
assume was a power surge took out the car charger, the charging circuit
in the iPaq and the GPS receiver
I have only had it two days but it seems to be much more responsive and
suffers from fewer lost signals. It starts up from cold quicker than I
can start the iPaq 3835 and load TomTom 3.
David |
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Guest
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| Posted:
Fri Nov 25, 2005 1:08 am Post subject:
Re: Wired GPS recommendation for PDA TomTom 3? |
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Apparently on date Wed, 23 Nov 2005 18:50:24 GMT, "Evil Uncle Chris"
<chris.macnamara@ntlworld.com> said:
| Quote: | I'm using a Dell Axim X30 PDA, with a TomTom windscreen mounted cradle.
I have a cheap wired GPS unit which plugs into the right hand side of the
cradle, connecting it to the PDA, and supplying the GPS with power via the
same cable.
|
Pretty much what I use, except I have a high quality, but old, Sapphire and a
new, but seemingly NMEA only, Sirf3 based wired smart antenna.
Axim X5 for both, Sapphire can go onto my iPaq 3630 as well.
The gist of this, Sirf3 gets lock about as quickly as the Sapphire, truth be
told, possible it is inferior even when on the move. Both kick in, though.
Axim is a continual PITA because it seems to lock the serial port in bizarre
ways.
I dunno if X30 is as bad as X5. Google says it is a Dell firmware issue, and I
believe it.
The PITA ritual I use to get around Dell is to do a reset of the PDA with
nothing plugged in. I load the application that came with the Sirf3 and tell it
to connect to the GPS which is, as yet, not plugged in to the Dell but is
powered so is getting on with acquiring lock.
Once the app is looking for it, I plug the antenna into the Dell and generally
it now loads up with the fix. I can enable waas and then explicitly disconnect
from the antenna and exit the program.
Other software can now connect to the antenna.
On the iPaq this shenanigans is avoided and the Sapphire seems a lot quicker to
get lock and to load software, despite being a slower PDA. Also the Sapphire
antenna is a lot smoother. This is probably because it runs at 57,600 baud
instead of 4800, so when updating a position from some instant time, the update
is in the PDA in a fraction of a second, while at 4800 baud it is still
chugging through the output strings most of a second later.
| Quote: | and general slow updating at roundabouts and junctions. I am guessing that
one of the newer SIRF Star III receivers would be better? I leave the GPS in
the car all the time, and keeping a BT GPS charged would be a disaster for
me..so, any recommendations, for the unit and retailer?
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Not many options as yet. The globalsat BR-355 I have works indoors but I think
would struggle in a multistory car park. Not sure there are any others
available.
If you want one now, they are available and may well work better than what you
have now, it's all relative. And 65 quid plus the trimmings is not too bad.
Hope this helps.
| Quote: | I have been briefly looking at the Holux GR-213 G-Mouse, on eBay for about
£50 UK, and £70 internet retailers. Happy to spend a bit more if it's worth
it.
Thanks for any advice
Chris
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Meindert Sprang
Guest
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| Posted:
Fri Nov 25, 2005 9:08 am Post subject:
Re: Wired GPS recommendation for PDA TomTom 3? |
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<Nospam@nowhere.com> wrote in message
news:r67co11o364vuq0fgqjill8p1b7hm8e46g@4ax.com...
| Quote: | Also the Sapphire
antenna is a lot smoother. This is probably because it runs at 57,600 baud
instead of 4800, so when updating a position from some instant time, the
update
is in the PDA in a fraction of a second, while at 4800 baud it is still
chugging through the output strings most of a second later.
|
Let's do some math: the longest position sentence (RMC) is about 78
bytes/characters. At 4800 baud, we have 480 chars/second. Thus one position
update at 4800 baud takes a whopping 0,163 second.....
Meindert |
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Guest
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| Posted:
Sun Nov 27, 2005 5:08 pm Post subject:
Re: Wired GPS recommendation for PDA TomTom 3? |
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Apparently on date Fri, 25 Nov 2005 09:13:29 +0100, "Meindert Sprang"
<mhsprang@NOcustomSPAMware.nl> said:
| Quote: | Nospam@nowhere.com> wrote in message
news:r67co11o364vuq0fgqjill8p1b7hm8e46g@4ax.com...
Also the Sapphire
antenna is a lot smoother. This is probably because it runs at 57,600 baud
instead of 4800, so when updating a position from some instant time, the
update
is in the PDA in a fraction of a second, while at 4800 baud it is still
chugging through the output strings most of a second later.
Let's do some math: the longest position sentence (RMC) is about 78
bytes/characters. At 4800 baud, we have 480 chars/second. Thus one position
update at 4800 baud takes a whopping 0,163 second.....
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That's clearly slower than a device that has completed the same task in a
hundredth of a second.
And in practice, there are GGA, GLL, GSA, GSV, RMC and VTG messages also being
sent, depending on how the device is set up (and whether you get any options
about that.)
In the real world, there is simply this:
Going around a roundabout, when the 57,600 device gives you an updated
position, that position is nearly exactly where you are at the instant it
happens. Whereas a 4800 baud device will take more like a third to a half a
second updating internally before the position is updated, and in practical
terms, that's twenty to thirty feet out of date by the time it shows on the
screen.
That's enough to misguide you about whether this is the right exit to take,
sometimes, and is, in all cases, quite apparent as a lag which doesn't happen
significantly at higher baud rates. |
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Meindert Sprang
Guest
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| Posted:
Mon Nov 28, 2005 1:08 am Post subject:
Re: Wired GPS recommendation for PDA TomTom 3? |
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<Nospam@nowhere.com> wrote in message
news:vudjo1h1n3or83eu6dhgtt4ecm9gninmt0@4ax.com...
| Quote: | In the real world, there is simply this:
Going around a roundabout, when the 57,600 device gives you an updated
position, that position is nearly exactly where you are at the instant it
happens. Whereas a 4800 baud device will take more like a third to a half
a
second updating internally before the position is updated, and in
practical
terms, that's twenty to thirty feet out of date by the time it shows on
the
screen.
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In the real world, one would look at the screen which exit to take, memorize
it as the <n>th exit, enter the roundabout and leave at the <n>th exit. I
mean, no sensible person would keep on driving on the roundabout until his
GPS says to leave it right? Knowing that position errors up to several 10's
of meters can exist due to unforeseen influences, right?
| Quote: | That's enough to misguide you about whether this is the right exit to
take,
sometimes, and is, in all cases, quite apparent as a lag which doesn't
happen
significantly at higher baud rates.
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Back to the math, 57600 or 4800 baud, you only get a new position update
every second, and that is too slow in itself to decide when to take which
exit.
Don't let the use of a GPS nav system shut down your own brain and common
sense!
Meindert |
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Guest
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| Posted:
Mon Nov 28, 2005 4:49 pm Post subject:
Re: Wired GPS recommendation for PDA TomTom 3? |
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Apparently on date Sun, 27 Nov 2005 23:51:17 +0100, "Meindert Sprang"
<mhsprang@NOcustomSPAMware.nl> said:
| Quote: | Nospam@nowhere.com> wrote in message
news:vudjo1h1n3or83eu6dhgtt4ecm9gninmt0@4ax.com...
In the real world, there is simply this:
Going around a roundabout, when the 57,600 device gives you an updated
position, that position is nearly exactly where you are at the instant it
happens. Whereas a 4800 baud device will take more like a third to a half
a
second updating internally before the position is updated, and in
practical
terms, that's twenty to thirty feet out of date by the time it shows on
the
screen.
In the real world, one would look at the screen which exit to take, memorize
it as the <n>th exit, enter the roundabout and leave at the <n>th exit. I
mean, no sensible person would keep on driving on the roundabout until his
GPS says to leave it right? Knowing that position errors up to several 10's
of meters can exist due to unforeseen influences, right?
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Blimey, that's like "back to the last millennium" for me. I expect accurate
fixes - a meter or two - and I expect the device to show these fixes at the
time they're happening.
I did have some old four channel thing once, it used to throw large errors,
tens of meters would have been not unknown. That would hide any lag, and I'd
have to regard the GPS as a general guide to position, not a measurement tool.
Anyway, having retrogressed from 57,600 baud on Sirf binary, to using NMEA at
4800 due to limitations of TomTom5, I've seen how this introduces an
error-inducing lag and would definitely not recommend this. I've expressed this
to anyone who will listen and learn from it so I'm done in this thread. Believe
that 4800 is more than fast enough if you want to - if it's all you've got then
I suppose that's for the best. |
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Meindert Sprang
Guest
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| Posted:
Mon Nov 28, 2005 5:08 pm Post subject:
Re: Wired GPS recommendation for PDA TomTom 3? |
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<Nospam@nowhere.com> wrote in message
news:q1nlo1p59dtu0t5sr2ihl821uv9vgef6n6@4ax.com...
| Quote: | Blimey, that's like "back to the last millennium" for me. I expect
accurate
fixes - a meter or two - and I expect the device to show these fixes at
the
time they're happening.
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Then you are expecting too much from a consumer grade GPS.
| Quote: | I did have some old four channel thing once, it used to throw large
errors,
tens of meters would have been not unknown. That would hide any lag, and
I'd
have to regard the GPS as a general guide to position, not a measurement
tool. |
Unless you have an expensive surveyor type GPS, that is exactly what it is.
| Quote: | Anyway, having retrogressed from 57,600 baud on Sirf binary, to using NMEA
at
4800 due to limitations of TomTom5, I've seen how this introduces an
error-inducing lag and would definitely not recommend this. I've expressed
this
to anyone who will listen and learn from it so I'm done in this thread.
Believe
that 4800 is more than fast enough if you want to - if it's all you've got
then
I suppose that's for the best.
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Ok, what does the datasheet of yout Sirf GPS at 57600 tell you about the
time between a receiving the satellite signals and spitting out a fix at
57600?
Meindert |
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