# Converting old stuff to NMEA



## Pub911 (Oct 25, 2007)

Can I make my ancient speed (SciTex) and Depth (DMI) sending units talk to my NMEA compatible devices? Are these outdated units really dead for good? 

C'mon, we're sailors aren't we? Isn't there a cheep-o way to make this work?

:laugher


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## sailingdog (Mar 19, 2006)

No, probably not.


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## hellosailor (Apr 11, 2006)

"Isn't there a cheep-o way to make this work?"

Sure there is. A chip log and a lead line, two pieces of string and you're in business. Whoever swings them can then convert them to NMEA on the fly.

Electronic conversion? No, there's a time to just give it up and walk away.


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## roline (Apr 7, 2000)

REAL Cheep way, no, but there is a way. I made an adapter board ($90) for the DMI speed transducer to talk to the ST60 speed display($80 on ebay), Raymarine makes the Seatalk to NMEA converter* E85001* ($160 new). 
I believe the DMI depth puck is a 200khz unit, if it is it can hook directly to a Raymarine ST60 depth instrument, I've seen them on Ebay for around $150 display only.
Once you have the converter, you can also hook it to a laptop for navigation software......You can do it for under $500 which is cheep when you consider the list prices on new ST60 instruments.....

Raymarine (Airmar) speed paddle wheel sensors have a hall effect sensor and 0 to 12 volt output. ( 12 volt power, signal, gnd) The older DMI have a 2 wire low level signal requiring excitation on the signal wire.

Did not know about the actisense NMEA converter, looks like a great product!


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## Pub911 (Oct 25, 2007)

I read this and went...

YAY!!!!.....ummm, awwwwwe nuts.

Ok. I guess I have to face into reality. In a similar post I asked if anyone had recommendations / experience on "active" Depth/Speed/Temp transducers or so-called "tri-"ducers when they do a hat-trick on D/S/T.

Airmar has a line running about $350. Anyone have experience with these or know of a better or cheaper unit?

Does Raymarine make a tri-ducer unit that talks SeaTalk? I can go that route as well if need be.

Thanks all.

Pub911


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## sailingdog (Mar 19, 2006)

Umm... Raymarine actually doesn't make transducers...*they use AIRMAR transducers,* so if Airmar makes it, Raymarine resells it... 



Pub911 said:


> I read this and went...
> 
> YAY!!!!.....ummm, awwwwwe nuts.
> 
> ...


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## Pub911 (Oct 25, 2007)

Thanks S-dog. Appreciate the OEM-insight.

P


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## ActisenseTechSupport (Feb 5, 2010)

*Actisense DST-2*

We have a product which will convert old depth speed and temp transducers into NMEA 0183 data, the DST-2
*
Depth* connects to a standard piezoelectric depth sounder crystal element using a 3-wire interface.
*Speed* connects to a standard 'paddle-wheel' hall-effect trancducer using a 3-wire interface.
*Temp *connects to a standard thermistor transducer using a 2-wire interface.
For example the DST-2 works with Airmar's DST800's.


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## sailingdog (Mar 19, 2006)

Please read and follow the Special Interest disclosure thread in the Boat Buying forum.


ActisenseTechSupport said:


> We have a product which will convert old depth speed and temp transducers into NMEA 0183 data, the DST-2
> *
> Depth* connects to a standard piezoelectric depth sounder crystal element using a 3-wire interface.
> *Speed* connects to a standard 'paddle-wheel' hall-effect trancducer using a 3-wire interface.
> ...


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## davester (Aug 8, 2007)

Tinley Electronics also makes a transducer/paddle wheel - nmea converter. There are some differences in features and price with the Actisense product. Tinley Marine Electronics.

I don't have any first-hand experience with either of these devices, but will probably install one in the next few months.


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## Pub911 (Oct 25, 2007)

Thank you all for your assistance. I've learned a lot as a result of your posts and some research I've done on my own. 

For the benefit of anyone else who may be interested, here are a few facts and observations:

"Old Stuff" like transducers and the like CAN have their signals converted to NMEA via a few nitch products from Tinley and Actisense; however, unless you are absolutely assured from the manufacturers above that your 'old stuff' is compatible, you assume the risk of it not working. And electronics are not usually accepted as returns for good reason: you may damage the new product AND your old-stuff if you hook it up wrong - a strong possibility if you can't get wiring details from the product you're purchasing.

Even if you manage to get compatibility assurance, you may end up spending more on these than if you simply replaced your current sending unit with an 'active' multi-sensing unit. By 'active' I mean, sending NMEA, and by multisensing, I mean a depth/speed/temp 'triducer' such as the AIRMAR DST800.

If you are just purchasing the sending unit (e.g. a triducer) be sure you have an open channel to receive NMEA input to your head-unit. NMEA networks can not be daisy-chained...an NMEA multi-plexer must be used to direct traffic between multiple NMEA talkers and if you are constrained to a single channel NMEA listener. This adds extra cost...roughly $300.

AIRMAR is the OEM behind MANY brand-name products. See the AIRMAR site for the cross reference of AIRMAR vs. Brand name products.

Bottom line: I'm going to purchase a new Garmin model 010-11051-10 (aka AIRMAR DST800) that converts it's signal to NMEA 0183 before it leaves the triducer. That means I can hook it straight into the NMEA input of my Raytheon Chartplotter using one of its two NMEA input channels. Retail this unit is $299. I found one, new, advertised at $213.

I hope this helps someone out there in a similar situation.


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## ActisenseTechSupport (Feb 5, 2010)

> "Old Stuff" like transducers and the like CAN have their signals converted to NMEA via a few nitch products from Tinley and Actisense; however, unless you are absolutely assured from the manufacturers above that your 'old stuff' is compatible, you assume the risk of it not working.


I would always recommend being comfortable with your purchases, if you are not sure the DST-2 will work with your old transducer then absolutely go with Pub911's advice and buy a new Active Transducer instead.
You will find a compatibility list in the manual for the DST-2, if your transducer is not in the list then care should be taken. If the transducer matches the criteria in the quote below I can see no problem using our DST-2 but as PUB911 said "you assume the risk" not us.
I would encourage anyone who has had success with a transducer not in the list to let us know so we can keep our compatibility list up to date and so less people have to decide to take the risk or shell out for a new transducer.


> Depth connects to a standard piezoelectric depth sounder crystal element using a 3-wire interface.
> Speed connects to a standard 'paddle-wheel' hall-effect transducer using a 3-wire interface.
> Temp connects to a standard thermistor transducer using a 2-wire interface.


Adding to this, Depth wires are +5v, Ground and transducer (signal/data).
Speed wires are +5v, Ground and pulse (signal/data).

As a foot note:


> AIRMAR is the OEM behind MANY brand-name products.


 and Actisense are the OEM behind MOST Airmar Active Transducers (Actisense = Active Sensors) we make the boards and write the algorithms (all the good ones that is, lol). The DST-2 connected to an old analogue Airmar transducer is the same as a new Airmar Active transducer for hardware and firmware.

As for Tinley I had a quick glance and it seems they are proven with B&G so between us most the major players are covered.


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## breezetrees (Jan 11, 2009)

I wrote a program for an arduino microcontroller that does the speed side of things, you can get to it here:

NMEA 0183 Speedometer

I haven't tried it with a real transducer yet, so consider it experimental. Arduino microcontrollers are cheap and easy to deal with if you're relatively handy, and the code is free.

-Mike


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## parturi (Sep 16, 2012)

Acisense TechSupport. Are depth transducers responses pulse-width modulation like speed transducers?


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## hellosailor (Apr 11, 2006)

parturi, AFAIK speed transducers are not PWM, they count the _frequency _of the pulses. More pulses in less time means faster. But the pulse width itself is not modulated, even if it is changed by the speed of the paddlewheel. Counting the frequency should always be simpler and cheaper than looking at the waveform. AFAIK.

And depth transducers typically look at the _time interval _between "ping" and "pong". Again, nothing is modulating pulses or their width. They're counting the time until a return signal comes back, not looking at the signal itself.


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## ActisenseTechSupport (Feb 5, 2010)

Depth Transducers are a certainly more complicated than Speed Transducers.
The real basics of depth transducers are as hellosailor said,


> depth transducers typically look at the time interval between "ping" and "pong".


 Additionally to this it is useful to check signal strength to help remove false echoes. Other processing can be needed as well to ensure good accurate readings.


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## parturi (Sep 16, 2012)

> They're counting the time until a return signal comes back, not looking at the signal itself.


Thansk for the answers. Are you referring with this phrase to the accoustic transducer's job? I was referring specifically more to the transducer output/return to the microprocessor.

Thank you!


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## ActisenseTechSupport (Feb 5, 2010)

The unit that processes the pong also generates the ping. This will be the head unit from the original sounder or the replacement (like the DST-2).
The analogue transducer itself acts like a speaker/microphone, it has nothing to do with what is send or received, it is just the conduit for the sounder.
So any 'counting of time between ping and pong' can only be referenced from the head unit (where the processor is), never the transducer.
The sounder should be calibrated for the time delay and signal strength loss caused by the cable.
The DST-2 operates best when the cable from the transducer is as short as possible.


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## parturi (Sep 16, 2012)

Thanks ActisenseTechSupport, very much!


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