Hi,

Does anyone know the format of the data returned from the masthead unit of a Autohelm
ST50?

Cheers
J

"J" wrote in message
...
Hi,

Does anyone know the format of the data returned from the masthead unit of
a Autohelm
ST50?

My gues would be SeaTalk, which is a proprietary protocol from RayMarine. A
reverse-engineered description can be found on
http://www.thomasknauf.de/seatalk.htm

Meindert

Meindert Sprang wrote:

"J" wrote in message
...
Hi,

Does anyone know the format of the data returned from the masthead unit of
a Autohelm
ST50?

My gues would be SeaTalk, which is a proprietary protocol from RayMarine. A
reverse-engineered description can be found on
http://www.thomasknauf.de/seatalk.htm

Meindert

The Autohelm ST50 masthead transducer is DUMB and analog with a five wire
connector. The smarts are in the display unit which outputs Seatalk.
Last Autumn I wrote a program that captures boat heading, wind speed and
relative direction off the seatalk bus and plots a scattergram wind rose.

I didnt get round to subtracting out the spead and COG from the GPS as I
wrote it purely for my own entertainment when alongside the berth to let
me check that the wind transducer was working properly after a thourough
clean and service without having to stay on deck to watch the readout.

While I was in the transducer, I noticed two apparently identical
quadrature sensing elements for the direction vane and a single sensor for
the speed cups.

From some troubleshooting info on the Rayithon site, I belive the
transducer runs on a regulated 8V feed from the display and outputs two
analog voltages for the direction, proportional to the Sine and Cosine of
the vane position. AFAIK the speed is a pulse waveform either 1 or 2
pulses per turn, although it might be a sinewave as well (The reference
was fairly obscure and I didnt have access to a scope on the boat.)

The sensors appear to be magnetic in nature and I belive uses hall effect
pickups. After removing the grub screws in the vane and cups , they can
be removed and you will then find that the two sensors are push fits in
the aluminium body with O ring seals and can be prized out carefully to
let you wash out he bearings. If you do dismantle it, the pickups appear
to be extremely fragile and unless you are experienced with delicate
mechanisms it would be extremely easy to break. Reassembling it is pretty
obvious, provided you hook up the display to setup the correct vane
direction before finally tightening its grub screw. Small adjustments may
be made by rotating the wind sensor slightly before pushing it fully home
in the Aluminium body, which you can do at the top of the mast. A
worthwile improvement in accuracy when heeled can be achived by balancing
the vane properly using a little metal foil of a wine bottle capsule or
some solder secured with a drop of superglue. I was surprised how much
was needed to balance it with its axis held horizontal.

--
Ian Malcolm. London, ENGLAND. (NEWSGROUP REPLY PREFERRED)
ianm[at]the[dash]malcolms[dot]freeserve[dot]co[dot]uk [at]=@, [dash]=- &
[dot]=.
*Warning* SPAM TRAP set in header, Use email address in sig. if you must.
'Stingo' Albacore #1554 - 15' Uffa Fox designed, All varnished hot moulded
wooden racing dinghy circa. 1961