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  #11  
Old 02-08-2010
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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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Old 02-10-2010
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Quote:
"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.
Quote:
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:
Quote:
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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Old 05-02-2010
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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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Old 09-16-2012
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Re: Converting old stuff to NMEA

Acisense TechSupport. Are depth transducers responses pulse-width modulation like speed transducers?
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Old 09-16-2012
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Re: Converting old stuff to NMEA

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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Old 09-17-2012
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Re: Converting old stuff to NMEA

Depth Transducers are a certainly more complicated than Speed Transducers.
The real basics of depth transducers are as hellosailor said,
Quote:
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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Old 09-17-2012
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Re: Converting old stuff to NMEA

Quote:
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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Old 09-18-2012
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Re: Converting old stuff to NMEA

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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  #19  
Old 09-18-2012
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Re: Converting old stuff to NMEA

Thanks ActisenseTechSupport, very much!
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