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Old January 21st 04, 06:18 PM
Lloyd Sumpter
 
Posts: n/a
Default Cheap and Nasty Knotmeter

Hi,

I still have the thru-hull from a long-dead knotmeter in Far Cove. I
may be able to dig up the partially-working paddle-wheel sender (iirc
needs a new paddlewheel).

Can I get a new sender, with proper documentation so I know how it
works, and hook it into my laptop? The Signet sender appears to put out a
voltage more-or-less proportional to speed, correct? So I would need a bit
of electronics (buffer/amp? and A/D) to put the value into the parallel
port of the laptop. Then a few runs with a GPS in still water should allow
me to calibrate it.

Where can I get data on what these senders actually put out?

Lloyd Sumpter
"Far Cove" Catalina 36 - waiting for new engine


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Old January 21st 04, 08:10 PM
Glen \Wiley\ Wilson
 
Posts: n/a
Default Cheap and Nasty Knotmeter

On Wed, 21 Jan 2004 09:18:16 -0800, "Lloyd Sumpter"
wrote:

Can I get a new sender, with proper documentation so I know how it
works, and hook it into my laptop?


I'm afraid I don't have anything like an answer to your question,
though I would have thought that the sender wouuld output pulses
rather than a variable voltage, leaving the instrument to count the
pulses. You can see some readymade data acquisition solutions at B&B
electronics http://www.bb-elec.com/ but I suspect the cost would
qiuickly approach that of a new instrument, if cost is your major
objective.

If it is pulse data, you might be able to attach (properly
buffered/amped) it to something like the RTS line of the serial port.
You can definitely capture RTS events if you take direct control of
the port, and probably even if you use the standard MSComm activeX
object. Since Windows is kind of crappy when it comes to doing
anything in real time, you'd likely lose pulses occasionally though.
I think you'd be better off to count them with a circuit and just pass
along the count. Don't know nuthin bout no parallel ports, though.

I'm actually more interested in your thought process. I have
something of a professional interest in displaying this sort of thing
on PCs. To date, I've worked with NMEA data, but I've been asked to
look into direct acquisition of certain data, so I'm wondering what
leads you to want to do this. Of course, if it's just cost, that's
pretty self-explanatory.

__________________________________________________ __________
Glen "Wiley" Wilson usenet1 SPAMNIX at worldwidewiley dot com
To reply, lose the capitals and do the obvious.

Take a look at cpRepeater, my NMEA data integrator, repeater, and
logger at http://www.worldwidewiley.com/
  #3   Report Post  
Old January 22nd 04, 12:54 AM
Harry Krause
 
Posts: n/a
Default Cheap and Nasty Knotmeter

Lloyd Sumpter wrote:

Hi,

I still have the thru-hull from a long-dead knotmeter in Far Cove. I
may be able to dig up the partially-working paddle-wheel sender (iirc
needs a new paddlewheel).

Can I get a new sender, with proper documentation so I know how it
works, and hook it into my laptop? The Signet sender appears to put out a
voltage more-or-less proportional to speed, correct? So I would need a bit
of electronics (buffer/amp? and A/D) to put the value into the parallel
port of the laptop. Then a few runs with a GPS in still water should allow
me to calibrate it.

Where can I get data on what these senders actually put out?

Lloyd Sumpter
"Far Cove" Catalina 36 - waiting for new engine


Sheesh, Lloyd, why don't you plumb that through-hull and add something
useful, like a baitwell?

Knotmeter...whyfor? You have a main GPS working of your mains, and a
backup GPS that works off its own little batteries, right?

Just interface one of the GPS units with your laptop.



--
Email sent to is never read.
  #4   Report Post  
Old January 22nd 04, 01:57 AM
Glen \Wiley\ Wilson
 
Posts: n/a
Default Cheap and Nasty Knotmeter

On Wed, 21 Jan 2004 18:54:21 -0500, Harry Krause
wrote:

Sheesh, Lloyd, why don't you plumb that through-hull and add something
useful, like a baitwell?

Knotmeter...whyfor? You have a main GPS working of your mains, and a
backup GPS that works off its own little batteries, right?


Maybe he read this:

http://www.sailnet.com/collections/a...3%20%20&tfr=fp

or this:

http://makeashorterlink.com/?U29531527

Or maybe he likes to use sailing polar diagrams that don't work with
VMG. Or just enjoys drawing current triangles. Or maybe he already
has a baitwell.
__________________________________________________ __________
Glen "Wiley" Wilson usenet1 SPAMNIX at worldwidewiley dot com
To reply, lose the capitals and do the obvious.

Take a look at cpRepeater, my NMEA data integrator, repeater, and
logger at http://www.worldwidewiley.com/
  #5   Report Post  
Old January 22nd 04, 02:40 AM
Lloyd Sumpter
 
Posts: n/a
Default Cheap and Nasty Knotmeter

On Wed, 21 Jan 2004 19:10:31 +0000, Glen "Wiley" Wilson wrote:

On Wed, 21 Jan 2004 09:18:16 -0800, "Lloyd Sumpter" wrote:

Can I get a new sender, with proper documentation so I know how it
works, and hook it into my laptop?


I'm afraid I don't have anything like an answer to your question, though I would
have thought that the sender wouuld output pulses rather than a variable
voltage, leaving the instrument to count the pulses. You can see some readymade
data acquisition solutions at B&B electronics http://www.bb-elec.com/ but I
suspect the cost would qiuickly approach that of a new instrument, if cost is
your major objective.

If it is pulse data, you might be able to attach (properly buffered/amped) it to
something like the RTS line of the serial port. You can definitely capture RTS
events if you take direct control of the port, and probably even if you use the
standard MSComm activeX object. Since Windows is kind of crappy when it comes
to doing anything in real time, you'd likely lose pulses occasionally though. I
think you'd be better off to count them with a circuit and just pass along the
count. Don't know nuthin bout no parallel ports, though.

I'm actually more interested in your thought process. I have something of a
professional interest in displaying this sort of thing on PCs. To date, I've
worked with NMEA data, but I've been asked to look into direct acquisition of
certain data, so I'm wondering what leads you to want to do this. Of course, if
it's just cost, that's pretty self-explanatory.


Thanks

Doing a bit more research, I've found the OLD Signet meters sent out an analog
voltage (they were basically small generators), but the newer ones, notably
Airmar (www.airmar.com) send out pulses.

Airmar even has some samples of how to interface with CMOS and TTL. I thought of
using one of the RS232 signals, but think I'll use the parallel port instead.
I'm using Linux, so I'll attach the pulse signal to the interrupt and use Unix
signals to minimize CPU time. (Airmar says they output pulses about 4.8/sec at 1
knot, so max is around 100pps, or 10ms between rising edges).

I think I'll be interfacing the GPS as well, so I can compare readings. I may
get energetic and write a "calibration program" that would average the two
readings and adjust the "fudge factor" for the knotmeter (assuming you push the
"calibrate" button, then run a specified distance, then back)

Only questions now a 1. will an Airmar sender fit in my existing thru-hull,
or do I have to buy a new one (apparently they're not expensive), and 2. sample
programs in C showing how to access parallel port in Linux.

Lloyd Sumpter
"Far Cove" Catalina 36



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Old January 22nd 04, 02:44 AM
Lloyd Sumpter
 
Posts: n/a
Default Cheap and Nasty Knotmeter

On Wed, 21 Jan 2004 18:54:21 +0000, Harry Krause wrote:

Lloyd Sumpter wrote:

Hi,

I still have the thru-hull from a long-dead knotmeter in Far Cove. I
may be able to dig up the partially-working paddle-wheel sender (iirc needs a
new paddlewheel).

Can I get a new sender, with proper documentation so I know how it
works, and hook it into my laptop? The Signet sender appears to put out a
voltage more-or-less proportional to speed, correct? So I would need a bit of
electronics (buffer/amp? and A/D) to put the value into the parallel port of
the laptop. Then a few runs with a GPS in still water should allow me to
calibrate it.

Where can I get data on what these senders actually put out?

Lloyd Sumpter
"Far Cove" Catalina 36 - waiting for new engine


Sheesh, Lloyd, why don't you plumb that through-hull and add something useful,
like a baitwell?

Knotmeter...whyfor? You have a main GPS working of your mains, and a backup GPS
that works off its own little batteries, right?

Just interface one of the GPS units with your laptop.


Already done that with the backup GPS.

You wouldn't know this sitting in your armchair, but in the Actual Ocean, there
are currents, waves, etc. which make the "speed over ground" calculated by the
GPS not the same as "speed through the water", which is what a knotmeter shows.
Now, for 50 points and what's behind Door #2: When testing a new engine for
performance, which speed value should you use? (cue Annoying Jeopardy Waiting
Music...)

Lloyd Sumpter
"Far Cove" Catalina 36

  #7   Report Post  
Old January 22nd 04, 03:42 AM
Harry Krause
 
Posts: n/a
Default Cheap and Nasty Knotmeter

Lloyd Sumpter wrote:

On Wed, 21 Jan 2004 18:54:21 +0000, Harry Krause wrote:

Lloyd Sumpter wrote:

Hi,

I still have the thru-hull from a long-dead knotmeter in Far Cove. I
may be able to dig up the partially-working paddle-wheel sender (iirc needs a
new paddlewheel).

Can I get a new sender, with proper documentation so I know how it
works, and hook it into my laptop? The Signet sender appears to put out a
voltage more-or-less proportional to speed, correct? So I would need a bit of
electronics (buffer/amp? and A/D) to put the value into the parallel port of
the laptop. Then a few runs with a GPS in still water should allow me to
calibrate it.

Where can I get data on what these senders actually put out?

Lloyd Sumpter
"Far Cove" Catalina 36 - waiting for new engine


Sheesh, Lloyd, why don't you plumb that through-hull and add something useful,
like a baitwell?

Knotmeter...whyfor? You have a main GPS working of your mains, and a backup GPS
that works off its own little batteries, right?

Just interface one of the GPS units with your laptop.


Already done that with the backup GPS.

You wouldn't know this sitting in your armchair, but in the Actual Ocean, there
are currents, waves, etc. which make the "speed over ground" calculated by the
GPS not the same as "speed through the water", which is what a knotmeter shows.
Now, for 50 points and what's behind Door #2: When testing a new engine for
performance, which speed value should you use? (cue Annoying Jeopardy Waiting
Music...)

Lloyd Sumpter
"Far Cove" Catalina 36


Ocean? No offense, but I thought you sorta wandered a 100 miles or so
from your home marina.



--
Email sent to is never read.
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Old January 22nd 04, 05:07 AM
Glen \Wiley\ Wilson
 
Posts: n/a
Default Cheap and Nasty Knotmeter

On Wed, 21 Jan 2004 17:40:24 -0800, "Lloyd Sumpter"
wrote:

I'm using Linux, so I'll attach the pulse signal to the interrupt and use Unix
signals to minimize CPU time. (Airmar says they output pulses about 4.8/sec at 1
knot, so max is around 100pps, or 10ms between rising edges).


Yeah, I expect that would be iffy on Windows. Sigh I was a unix
internals guy for Amdahl back in the 80's. SVID4 timeframe. I got
out of it just in time to avoid making money when *nix got popular. I
need to get a Linux box just for old times sake.

I think I'll be interfacing the GPS as well, so I can compare readings. I may
get energetic and write a "calibration program" that would average the two
readings and adjust the "fudge factor" for the knotmeter (assuming you push the
"calibrate" button, then run a specified distance, then back)


I've considered that as well. Right now, I just use my speed and SOG
graphs to eyeball the number. Since my KM and DS lose their fudge (I
can't believe I just typed that) factor when power is removed for too
long, I wind up doing it every season or so. Have fun!

__________________________________________________ __________
Glen "Wiley" Wilson usenet1 SPAMNIX at worldwidewiley dot com
To reply, lose the capitals and do the obvious.

Take a look at cpRepeater, my NMEA data integrator, repeater, and
logger at http://www.worldwidewiley.com/
  #9   Report Post  
Old January 22nd 04, 03:26 PM
Backyard Renegade
 
Posts: n/a
Default Cheap and Nasty Knotmeter

"Lloyd Sumpter" wrote in message .. .
Hi,

I still have the thru-hull from a long-dead knotmeter in Far Cove. I
may be able to dig up the partially-working paddle-wheel sender (iirc
needs a new paddlewheel).

Can I get a new sender, with proper documentation so I know how it
works, and hook it into my laptop? The Signet sender appears to put out a
voltage more-or-less proportional to speed, correct? So I would need a bit
of electronics (buffer/amp? and A/D) to put the value into the parallel
port of the laptop. Then a few runs with a GPS in still water should allow
me to calibrate it.

Where can I get data on what these senders actually put out?


Take a powered up down to the local auto dealer and see if they will
let you hook it up to the occilliscope, assuming the guys there know
how to do something other than hook up the probes and run a "self
test" on the car. You will be able to see if it is digital or analog,
and how much current it generates, how it sends the information to the
cpu, etc...
Scotty

Lloyd Sumpter
"Far Cove" Catalina 36 - waiting for new engine

  #10   Report Post  
Old January 22nd 04, 08:22 PM
Terry Spragg
 
Posts: n/a
Default Cheap and Nasty Knotmeter

Your error (difference) log would make a database of tidal /
current info, I should think.

"Analogue" or digital? A magnet passing a coil produces
sinusoidal output. It's a guitar string, folks! Fancy ones use a
threshhold detector (a schmidt trigger) and produce a pulse
(range adjustable by setting a 555 pulse circuit to vary duty
cycle) integrate output into an rc network to drive a d'Arsonval
movement, or just switch capacitors. (I can provide basic
d'Asonvals for about 10 bucks plus shipping, maybe a little less)
You can't just rectify the ac output, because you would lose the
bottom end of the speed output, because the low frequencies are
also a lower level output, and you need a rectifier to feed the
meter, lest it null. A forward biased (by about 0.7vdc)
rectifier would help. The speed scale would not be linear, so a
dc compensation amplifier might be needed, and that would need
readjustment occasionally. Ain't analogue grand?

Dragging a fishing weight on 50 feet of line over the taffrail
pulling against a calibrated spring scale is cheap and dirty. A
fishing scale might work, if you usually catch fish under a
pound. If you ask to buy a gram scale, black helicopters will
follow you silently home.

A trolling or other small dc magnet style motor and some
alligator clips might actually recharge a battery through an
ammeter calibrated in knots. You could drive a clockwork dial to
indicate distance, not considering current or wind drift. Leave
your tranny in drive, pull the spark plugs, and let her rip, eh?
If you changed the cam timing on the exhaust valves, could you
pump air with the engine? Would venting the air under the hull
reduce water friction, even extend hull speed restrictions if
vented at the front and rear of the hull?

Russian torpedo makers seem to think it works.

Could you test this concept using the engine in neutral just for
it's exhaust gas? Even a genny?

How about a car alternator, chimney rod and propellor rig hanging
off the transom taffrail? Epoxy a small magnet (and a counter
weight?) inside the rotor to ensure the alternator always starts
up. An ammeter would reflect your speed. Free electricity? You
would have to maintain a steady load on the output, if you want a
speed indication. Perhaps electrolysing water to make hydrogen
fuel for you engine or a standby bag of H2 for your genny or fuel
cell? A bridle tethered tube bearing rig might extend the life of
the alt. bearings.

'Digital' outputs come from hall effect 'magnets', which do not
make an output until a certain magnetic field is sensed, then
they put out a pulse. The difference in the sending units is the
Hall effect ones have a magnet mounted near a coil pickup on the
housing. The wheel contains a parasitic-active transducer, a
quantum re-radiator that puts out a consistant pulse. Analogues
lack the magnet on the housing.

Either style can drive either type of display, if the right
electrics are hitched.

Fully digital systems are more complicated, using phase locked
loop i.c. clocks to help generate segmented displays using driver
logic designed by boolean principals.

Terry K

Lloyd Sumpter wrote:

On Wed, 21 Jan 2004 19:10:31 +0000, Glen "Wiley" Wilson wrote:

On Wed, 21 Jan 2004 09:18:16 -0800, "Lloyd Sumpter" wrote:

Can I get a new sender, with proper documentation so I know how it
works, and hook it into my laptop?


I'm afraid I don't have anything like an answer to your question, though I would
have thought that the sender wouuld output pulses rather than a variable
voltage, leaving the instrument to count the pulses. You can see some readymade
data acquisition solutions at B&B electronics http://www.bb-elec.com/ but I
suspect the cost would qiuickly approach that of a new instrument, if cost is
your major objective.

If it is pulse data, you might be able to attach (properly buffered/amped) it to
something like the RTS line of the serial port. You can definitely capture RTS
events if you take direct control of the port, and probably even if you use the
standard MSComm activeX object. Since Windows is kind of crappy when it comes
to doing anything in real time, you'd likely lose pulses occasionally though. I
think you'd be better off to count them with a circuit and just pass along the
count. Don't know nuthin bout no parallel ports, though.

I'm actually more interested in your thought process. I have something of a
professional interest in displaying this sort of thing on PCs. To date, I've
worked with NMEA data, but I've been asked to look into direct acquisition of
certain data, so I'm wondering what leads you to want to do this. Of course, if
it's just cost, that's pretty self-explanatory.


Thanks

Doing a bit more research, I've found the OLD Signet meters sent out an analog
voltage (they were basically small generators), but the newer ones, notably
Airmar (www.airmar.com) send out pulses.

Airmar even has some samples of how to interface with CMOS and TTL. I thought of
using one of the RS232 signals, but think I'll use the parallel port instead.
I'm using Linux, so I'll attach the pulse signal to the interrupt and use Unix
signals to minimize CPU time. (Airmar says they output pulses about 4.8/sec at 1
knot, so max is around 100pps, or 10ms between rising edges).

I think I'll be interfacing the GPS as well, so I can compare readings. I may
get energetic and write a "calibration program" that would average the two
readings and adjust the "fudge factor" for the knotmeter (assuming you push the
"calibrate" button, then run a specified distance, then back)

Only questions now a 1. will an Airmar sender fit in my existing thru-hull,
or do I have to buy a new one (apparently they're not expensive), and 2. sample
programs in C showing how to access parallel port in Linux.

Lloyd Sumpter
"Far Cove" Catalina 36


--
Terry K - My email address is MY PROPERTY, and is protected by
copyright legislation. Permission to reproduce it is
specifically denied for mass mailing and unrequested
solicitations. Spamspoof salad by spamchock TM - SofDevCo



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