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David G. Bell -- SF Fan, Filker, and Punslinger.
On the horizon, a carrier task force of the Salvation Navy was
turning into the wind, preparing to launch Zeppelins.
> The key problem is whether or not you can use an external aerial. I've
> seen instructions for a cradle for a hand-held which reradiates a signal
> for an external aerial, but being able to plug in is far better.
That may have been the case a few years ago but not any more. Current
receivers do not need external antenna in the vast majority of
situations.
> The laptop connection can also cost more than the actual receiver. Some
> kit has a connector you can easily make up from parts. Others have a
> proprietary connector.
USB GPS need no additional connectors, indeed even serial GPS don't
need any additional connectors?
> I have a Garmin hand-held with both these problems, but I bought a
> combined serial/power lead at the time. I'm not sure that the descendant
> models even use the same connector.
For PDA's, Bluetooth is the solution these days.

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Darren Griffin
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Ian Rawlings - 29 Aug 2007 09:20 GMT
> USB GPS need no additional connectors, indeed even serial GPS don't
> need any additional connectors?
The serial GPS I have needs a power connector, unlike USB, RS232
doesn't supply significant amounts of welly. It doesn't need much
power, it can draw it from the keyboard socket of a PC for example.
This was a pre-USB GPS.

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Blast off and strike the evil Bydo empire!
Dave Liquorice - 29 Aug 2007 14:19 GMT
> The serial GPS I have needs a power connector, unlike USB, RS232
> doesn't supply significant amounts of welly.
2.5W isn't a great deal of welly on USB (500mA @ 5v). Admittedly you
couldn't get that from RS232 (100mA @ 24v) but you can draw power from the
control lines of an RS232 port. The snag is you have to make sure you set
up the relevant port pins to the correct levels in the software that is
controlling the serial port.

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Cheers new5pam@howhill.com
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Ian Rawlings - 29 Aug 2007 15:22 GMT
> 2.5W isn't a great deal of welly on USB (500mA @ 5v).
It's still half an amp, trying to get that out of an RS232 line driver
which isn't really designed for it isn't a good prospect for a company
building a commercial product as they'd end up having to replace some
computers as there will be a proportion of their customer base whos
serial ports get popped.
I've got a radio clock that's driven from the serial port control
lines, so I know it can be done, it's just not a good idea especially
if you are trying to sell to a wide market of varied machines. Not
that they have RS232 serial ports these days anyhow, so this is
yesterday's problem ;-)

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Blast off and strike the evil Bydo empire!
Dave Liquorice - 29 Aug 2007 18:14 GMT
>> 2.5W isn't a great deal of welly on USB (500mA @ 5v).
>
> It's still half an amp,
Except to get 2.5W from RS232 you only need to draw just over 100mA as you
have 24v available. 100mA is still beyound the spec of RS232 though. B-)
> Not that they have RS232 serial ports these days anyhow, so this is
> yesterday's problem ;-)
Yeah, PITA not having a simple interface available. Won't be long before
the only IO is USB. B-(

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