Hi Steve,

Interesting ideas. Thanks. My sailboat's battery won't allow most, like
leaving a notebook PC running all night or an inverter. And I sure don't
want to have stuff operated by batteries that need to be replaced if it can
be avoided.

Unlike your GPS 128, my handhelds (2- GPS 48s) do not have an alarm
connection. But I think that the GPS 128 would be the way to accomplish what
I want. I have a loud 12vdc piezo siren that draws 150mA -- will the GPS 128
run it? Do you know of other smallish, inexpensive GPS receivers that have
an anchor drag alarm-out feature? I'd sure like to find a little one that
has it plus is WAAS enabled. I don't need chartplotting.

Thanks,
Len
Florida USA





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"Steve Cowley" wrote in message
...
Hi Len,
several options, ranging from simple to complex!
theres probably a commercial system out there, but I like making stuff:

1) hows about a baby alarm\monitor?and turn the volume up?

http://www.argos.co.uk/webapp/wcs/st...roductId=56105

2) If you can find a mains powered buzzer with a plug on the end of it,
simply get one of those remote controlled home automation plugs

http://maplin.co.uk/products/module....duleno =32076
and cannibalise the remote control to hook it up to the GPS alarm line.
You
could get it to turn the lights on too then!

3) My GPS has an alarm output line on it, which I use to switch a relay on
a
simple radio tramsmitter module. The receiver sits anywhere on the boat
and
simply latches on a buzzer when the alarm condition is on.
I have a Garmin GPS128
http://www.garmin.com/manuals/82_OwnersManual.pdf
page 63 shows the alarm line.
I had some remote control modules knocking about from Maplin here in the
UK

http://www.maplin.co.uk/products/mod...8&P roducts=4
(initially from rf solutions)

tie the transmitter switch to the output from the GPS alarm line (how good
is your electronics?). Put a relay on one of the reciever outputs to drive
a
loud buzzer (make sure the receiver output latches on). I then glued the
receiver to a 12V power adapter and plugged it in in the cabin (uses about
10mA on standby) it's got a battery in it too which will last a few days.
This works great - no false alarms as the keyfob transmitter uses a code
to
transmit. Problem with this is that you can't tell when the unit is out of
range, other than testing it. Solution is further down.

3) If your GPS doesn't have an alarm line, you could canibalise one of the
whistle-responding keyrings to get this to switch the transmitter - just
pop
it next to your GPS at night - again make sure the receiver latches on.
(and
your alarm goes off continuously until you switch it off)

4) If you are better at electronics, you can use simple radio modules to
transmit the alarm line state from the GPS over a link AND have some
monitor
for if the wireless link goes dead. I have built a version using
Radiometrix
radio modules which have received signal strength indicators
http://www.radiometrix.co.uk/products/rx2a.htm
You can't simply plug the GPS alarm line into these though, as there are
duty cycle restrictions (data can't be a "1" for more than 50% of the time
I
think) so you have to encode it - one way is with their encoder chips, but
I
just used a 555 astable multivibrator circuit to make a square wave signal
to transmit, and used the alarm output line from the GPS to cut off the
power to the transmitter. At the receiver end, simply hook a
relay\transistor to the RSSI indicator line. If it goes out either the
radio
link is bad, or the anchor alarm has gone off, both of which you want to
be
awake for.

If you are really have too much time on your hands, you can do it with
NMEA.
I have written a custom anchor alarm program for use with my laptop and
wireless NMEA links (see previous message "Wireless navigation - it
works!"
7th Jan 04,) which simply gets the current position from NMEA sentences
transmitted from the GPS upstairs, compares the current position with a
previous stored position (stored when you press the 'set' button), does
the
maths to see if you have drifted a certain distance away from your
setpoint
(just like your GPS drag alarm.) and beeps at you if it does
Good thing about this method is you can also have an alarm on the depth
reading from your echo if you have this wired up to NMEA too, although the
drag alarm does the real work. Bad thing is you need a laptop plugged in
all
night AND the wireless NMEA links\NMEA downstairs AND the software
I could give you the software, but it'll cost you £800 (GBP) as that is
how
much a licence for the language I wrote it in costs (no-I didn't use
++ -
I wrote it whilst on breaks at work!)
You might as well go for that OzziExplorer program!

Hope this helps

Steve Cowley
Manchester, England


"Len Krauss" wrote in message
...
My GPS (with an anchor drag alarm feature) is not located in sleeping
berth.
Even even if it were, its alarm is barely audible, and certainly not
adequate to arouse a person from a sound sleep (unless the GPS were
strapped
to one's ear.). Additionally, a GPS antenna wire would need to be run to
the
berth -- not a big problem, but what's the point if one can't hear the
alarm
anyway.

Perhaps there's some kind low-power amplifier that could be placed next
to
the GPS, or possibly a transmitter with remote alarm receiver. But it
might
need to be tunable, so just any kind of noise doesn't set it off.

I was hoping that there might be a defined NMEA sentence output by the
GPS
when an anchor drag condition is sensed, but none exits from what I've
been
told. If there were, it might be possible to detect it in order to
trigger
a
loud alarm of some type.

Would welcome any and all suggestions for off-the-shelf or custom anchor
drag alarm systems.

Thanks,
Len
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