NMEA 183 depth/speed/distance to Analogue conversion

[neilandshiv]

ok - terminology - for stdout read whatever what there is on a Ardunio for seeing a simple print of a variables value

 

[ianj99]

Thanks again for all responses:
Sounder manual says:
Depth range 0.9 to 137m
Transmitted Power 50 watts rms
Frequency of operation 171kHz nominal
Sounding rate 2 to 20 pulses per second, automatically adjusted.
And it basic unit uses 270ma

Assume sounding rate is the key:
at 0.9m echo takes 1.2ms, so assume its doing 20 per second that's every 50ms
so it leaves a good 45ms to send the pong back to the instrument and it be processed and displayed before the next ping.
Arduino can certainly easily run loops faster than this and control time delays down to 10micro seconds accurately. So it depends on if the Arduino can detect a pin going high from the sounder sending the ping, and if setting a pin to high for mimicking the pong will be enough.

I don't have a scope put may try to use the Arduino to just read the ping pongs and see if I can output that to stdout, if I can't find someone with a scope I could borrow one.

You make it sound simple!
1)Attenuate the pings so you don't blow the Arduino AND isolate the receiver so you don't blow it as well.
2) Amplify and probably band pass filter the received very small signal to a level to drive the Ard
3) I doubt a single pulse will suffice for the B&G to recognise as a return signal - its expecting a very small 171Khz signal of several cycles I would imagine.

There's a lot trial and error without a scope - even one of the £70 Ebay pocket scopes would be very useful.

 

[neilandshiv]

Hi Ianj99
Thanks for the tips - no I'm sure its not that simple but I have to start somewhere, just intending to start simple, and learn as I go with help from good folk on the forum like yourself and Pete.
Have you any particular recommendation for a Ebay pocket scopes.
Also if the pings are less than 5V the Arduino should be ok shouldn't it, or 3.3v for the Due.
Obviously if I get a working solution I will make it available here for anyone else could use it

 

[GHA]

Hi Ianj99
Thanks for the tips - no I'm sure its not that simple but I have to start somewhere, just intending to start simple, and learn as I go with help from good folk on the forum like yourself and Pete.
Have you any particular recommendation for a Ebay pocket scopes.
Also if the pings are less than 5V the Arduino should be ok shouldn't it, or 3.3v for the Due.
Obviously if I get a working solution I will make it available here for anyone else could use it

These are handy little scopes, great to have onboard



http://m.ebay.co.uk/itm/380707009106

 

[prv]

Also if the pings are less than 5V

I found a document which quoted 600v...

That was a scientific paper, so I don't know how similar the apparatus would be to an off-the-shelf small-boat transducer. But I did also find an installation manual for a boat product that warned of "high voltage" in the transducer wires.

You're not dealing with TTL digital electronics here, so can't make this kind of assumption.

Pete

 

[ianj99]

Hi Ianj99
Thanks for the tips - no I'm sure its not that simple but I have to start somewhere, just intending to start simple, and learn as I go with help from good folk on the forum like yourself and Pete.
Have you any particular recommendation for a Ebay pocket scopes.
Also if the pings are less than 5V the Arduino should be ok shouldn't it, or 3.3v for the Due.
Obviously if I get a working solution I will make it available here for anyone else could use it

I prefer Amazon so here is the latest 2channel model:
http://www.amazon.co.uk/SainSmart-P...qid=1460625242&sr=1-1-catcorr&keywords=dso202

Pete is right. The Piezo transducers are capacitive and require high voltage low current pulses so you should start with a 100:1 attenuator between the sounder output and the scope (100k:1k is near enough) to establish what attenuation is required to keep the Arduino from being damaged.

(I am assuming the transducer is the old school single wire Piezo type and probably also not a good idea to hold onto the bare end when its transmitting even though the pulses are short and very low current!)

 

[Noahsdad]

I think Tinley Electronics make a box to allow installation of an Airmar NMEA log transducer in a B&G analog system.

 

[prv]

I think Tinley Electronics make a box to allow installation of an Airmar NMEA log transducer in a B&G analog system.

So they do, good spot. They don't seem to have the depth-sounder equivalent though, which might imply that it's more difficult to do what the OP has in mind.

However, they do seem to have a compatible replacement depth transducer :encouragement:

Sounds like the OP needs to talk to these folks.

Pete

 

[ianj99]

However, they do seem to have a compatible replacement depth transducer :encouragement:
Pete

Would save a lot of trial & error development. I can forsee that generating the 170khz return pulse substitute at just the right time could be more of a challenge.

Nmea speed to analogue is easier - most paddle wheel sensors produce abut 5Hz per knot.

 

[neilandshiv]

I asked Tinley if they could provide a conversion from NMEA to analogue for our Hornet Log and Hectra/Hornet Depth but they were not interested. Said it was cheaper to dump the lot and buy new, which it is if you are happy with one multifunction display, but not if you want the info on separate displays, and with repeaters.

Their NMEA to B&G Analogue converter is to later analogue version as far as I can tell
(otherwise they would have just told me I could buy it when I enquired) and their NMEA Paddlewheel mentions B&G Hydra/Hercules not the Hornet log

Thanks for the voltage warning and scope recommendations. Think its a 3 wire connection to the echo transducer but will check at the weekend.

 

[pvb]

Think its a 3 wire connection to the echo transducer but will check at the weekend.

Think it only needs 2 wires; might the third wire be a water temperature sensor?

 

[ianj99]

Think it only needs 2 wires; might the third wire be a water temperature sensor?

or 2wires for the sensor + screen?

 

[pvb]

or 2wires for the sensor + screen?

Lots of old simple depth transducers use coax.

 

[neilandshiv]

2+ screen I think - definitely not coax
don't think they did echo+temperature transducer in one unit in 1975!
Could one wire be the outgoing sounder to transducer, and the other the returning signal
- sorry if its a dumb question - did say I know sod all about electronics - just watching how to use scope stuff on utube!

As a starter this weekend before I get a scope if I put volt meter on big voltage scale (0-1000v) across the two wires, or from each wire to screen will I get anything?
Will I break anything?

 

[ianj99]

2+ screen I think - definitely not coax
don't think they did echo+temperature transducer in one unit in 1975!
Could one wire be the outgoing sounder to transducer, and the other the returning signal
- sorry if its a dumb question - did say I know sod all about electronics - just watching how to use scope stuff on utube!

As a starter this weekend before I get a scope if I put volt meter on big voltage scale (0-1000v) across the two wires, or from each wire to screen will I get anything?
Will I break anything?

A voltmeter won't be any use - its a very short pulse so although you may getting a brief change in reading, it won't be useful.

Its possible the receive sensor is separate from the tranmitter, but its not the usual way. I would guess the transducer is not earthed and is capacitively coupled to the ping pulse generator and receiver / amplifier so you would see signals of opposite polarity with respect to the screen on the 2 wires if that is how it is wired up. A scope is really essential.