Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Search this Thread Rate Thread Display Modes
Old 14-01-2018, 10:23   #1
Registered User
 
sy_gilana's Avatar

Join Date: Jan 2005
Location: On board
Boat: Van de Stadt 50'
Posts: 1,207
Send a message via Skype™ to sy_gilana
Electronic Gurus please step up.

So I have an old Raymarine L755 sounder.
The speed transducer (Airmar) is a Hall Effect but two-wire system unique to Ray. I suspect it is a current sensing square wave output.
I have been given a new replacement B744V txd from a Furuno.
The Depth and Temp are working fine, but the speed is not, because the Furuno uses a voltage sensing square wave.

There must be a way to convert the 3 wire Vsense to a 2 wire Isense even if it requires a little add on circuit.

Your thoughts please?

The two diagrams refer.
Attached Thumbnails
Click image for larger version

Name:	fur-cct.jpg
Views:	149
Size:	75.2 KB
ID:	162235   Click image for larger version

Name:	Ray-cct.jpg
Views:	128
Size:	51.4 KB
ID:	162236  

__________________

__________________
Tight sheets to ya.
http://gilana.org
sy_gilana is online now   Reply With Quote
Old 14-01-2018, 12:46   #2
Registered User

Join Date: Sep 2017
Posts: 593
Re: Electronic Gurus please step up.

Hi sv_gilana,

I think you are on the right track. The hall effect IC most likely has an open collector NPN transistor as it's signal output. When the magnet is near, the transistor is on, pulling the signal to ground. It is up to the circuit designer to do something with this.

In the 2-wire Raymarine case, they connected a zener diode on the power input to the hall effect IC and to the signal ouutput of the IC. This is a quick and dirty way of using the DC power for the hall effect chip as a signal too. No doubt in the main unit, there is a limiting resistor in the +V supply, across which it can read a voltage drop. (converting the current signal to voltage signal)

Assuming the old connector-new connector wires can be rearranged appropriately, it seems to me all you would need to do is add a zener diode. This is a special kind of diode (the symbol has the extra wiggle lines at the cathode line on the point of the triangle) which is designed to operate in reverse, thus providing a fixed voltage drop. This fixed drop is what occurs when the hall effect switch in on.

The trick will be to determine the voltage of the zener to get the correct one. Ideally, you would steal this from the old module and simply connect it from the signal wire of the new module to ground. (with the cathode bar connected to the signal line, the other end to ground.) This could be done on either end of the cable, though I think noise immunity would be best if you could connect it on the sensor end.

Essentially, the green wire in the new Furuno diagram will not connect to anything but the anode (non-bar side) of the zener diode you install. The cathode (bar side) of the zener diode will connect to the Raymrine Voltage/sense connector, which was pin 1 on the Raymarine schematic. (I assume you have rewired the connector, and the extra (green) wire of the new sensor module had no place to go?) I can draw a schematic if t would make more sense.

If you cannot steal the zener diode from the old circuit, you could guess. However, if you guess too low, you could fry the sensing resistor in the main unit. If you guess too high it won't sense. Zeners are so cheap, if guessing, I would do it like this: choose several zener diodes, starting with zener voltage ratings (Vz) close to the V+ supply voltage going to the speed sensor. I would measure this with a meter. (pin 1 to ground of the Raymarine connector) If the voltage is, say 12V, then start your zener trial at something around a 10V zener. (make sure the cathode, the bar, is connected to +V) If that doesn't sense the speed, then swap out the zener for a 9V one and try again. Keep going lower until it senses. You should not have to go under 50% of the V+ value. (IE don't go less than 6V if the V+ is 12 V)

Good luck!

-Cyan
__________________

cyan is online now   Reply With Quote
Old 14-01-2018, 13:34   #3
Registered User
 
sy_gilana's Avatar

Join Date: Jan 2005
Location: On board
Boat: Van de Stadt 50'
Posts: 1,207
Send a message via Skype™ to sy_gilana
Re: Electronic Gurus please step up.

What a fantastic response, it makes perfect sense (pun intended)
Having worked on RayXX stuff a lot (Just keeping mine alive) I suspect they are using 8V Zeners, I have a few lying around from an old wind speed sensor, and why would they have not used that circuit in their water speed sensor???

Going to save your answer, and thank you once again!
__________________
Tight sheets to ya.
http://gilana.org
sy_gilana is online now   Reply With Quote
Old 14-01-2018, 16:22   #4
Registered User

Join Date: Sep 2017
Posts: 593
Re: Electronic Gurus please step up.

Hi sv_gilana,
The 8V zener is probably a good guess, but without knowing the supply voltage to the hall effect sensor and the other component values, I would be hard to know for sure.

Also, my typing doesn't keep up with my thoughts sometimes, and I noticed a mistake. (though you probably figured it out)

I wrote:
"Ideally, you would steal this from the old module and simply connect it from the signal wire of the new module to ground"


And I SHOULD have written:
"Ideally, you would steal this from the old module and simply connect it from the signal wire of the new module to the + VOLTAGE/SIGNAL (SPEED) pin of the Raymarine main unit.
cyan is online now   Reply With Quote
Old 14-01-2018, 16:41   #5
Registered User
 
sy_gilana's Avatar

Join Date: Jan 2005
Location: On board
Boat: Van de Stadt 50'
Posts: 1,207
Send a message via Skype™ to sy_gilana
Re: Electronic Gurus please step up.

Hi again, yes, I had spotted that, not when I read it, but when I compared the two ccts, it was obviously a brain-fart. I have written to the MFG of the sensor asking quite brazenly for the value of the Zener. They are usually excellent at support, but we will see how far this gets, as I am the worst type of customer anybody could want, I just try to make do with the resources I have at my disposal, namely my rapidly reducing wits....

The reason I suspect the 8v one is that Rayxx would most likely have asked Airmar to build it that way, because they had a ready-made solution for wind speed measurement. Why waste money on a new design....hey, that leads me to think... If I connect my wind speed instrument to the fishfinders speed input, it could work, that would prove the point. AHA!

...and thank you once again.
__________________
Tight sheets to ya.
http://gilana.org
sy_gilana is online now   Reply With Quote
Old 15-01-2018, 09:26   #6
Registered User

Join Date: Dec 2016
Location: LA/northern Utah/Wisconsin/Chicago/at anchor La Paz, BCS
Boat: Hans Christian 38 Mk II
Posts: 68
Images: 1
Re: Electronic Gurus please step up.

Great discussion, thanks to you both
AndyEss is offline   Reply With Quote
Old 15-01-2018, 19:09   #7
Registered User
 
sy_gilana's Avatar

Join Date: Jan 2005
Location: On board
Boat: Van de Stadt 50'
Posts: 1,207
Send a message via Skype™ to sy_gilana
Re: Electronic Gurus please step up.

Hello again CYAN.

I have been doing some more digging. The attached screen-shots refer to the Rayxx DSM300 echo sounder module, which, apparently can use the same TXDs as the L755.

The diagram and associated modus operandi indicate a square wave, edge counted, between 10 and 5.1Vdc. The existing Furuno one will send supply V to 0V through the Hall switch.

Is this any use to you to confirm that the Zener trick will work and if so, what possible values would it be?
Attached Thumbnails
Click image for larger version

Name:	spdlogic.jpg
Views:	52
Size:	44.5 KB
ID:	162351   Click image for larger version

Name:	speed_sense.jpg
Views:	57
Size:	28.2 KB
ID:	162352  

__________________
Tight sheets to ya.
http://gilana.org
sy_gilana is online now   Reply With Quote
Old 16-01-2018, 00:00   #8
Registered User

Join Date: Sep 2017
Posts: 593
Re: Electronic Gurus please step up.

Hi sv_gilana,

The new information is interesting. The text suggests that our mystery zener could well be a 5.1V zener, which would then be the diode of choice to connect the extra sense line to the +V pin. However the new schematic is a little confusing, as the opamp appears to be set to a reference of 2.5V (5V divided through two 22K resistors) I don't think this would work with a 5.1V to 10V input signal. Possibly the +5V supply feeding D9 and R92 is not really 5V? (not sure about the compatibility of this new diagram, sorry)

In any case, a 5.1V zener might be the best guess.

NOTE:
It would be awesome of someone here has a Raymarine L755, with a 2-wire speed sensor, who could put a scope on the sense line and tell us the voltages of the square wave, high and low.
cyan is online now   Reply With Quote
Old 16-01-2018, 07:36   #9
Registered User
 
sy_gilana's Avatar

Join Date: Jan 2005
Location: On board
Boat: Van de Stadt 50'
Posts: 1,207
Send a message via Skype™ to sy_gilana
Re: Electronic Gurus please step up.

Hi CYAN.

Im pretty sure about the +5v supply if I look at the other voltages on the rest of that board. Here's a thought, I am not an electronics guy but, whenever I see gangs of diodes all pointing the same way, I think rectifier... So in the last cct diagram posted, the left side is the supply to the Hall IC, and it is also the signal from the Hall IC, (remember it refers to the Rayxx method) Possibly, the pulsating voltage drop from the sensor circuit causes a differential, that is rectified into the LM393D which would create a binary 1 output of both rising and falling edges of the dirty signal coming in?

In any case, that is all theory, and this thread is better than Sudoku. I am going to dig for diodes soon, and do a test.

I got a reply from Airmar, but it was not the specs of the Zener in their Rayxx txd, they sent a test method for the Furuno txd, which I have already proved.

Nice to meet you, this has been fun and its not over yet....
__________________
Tight sheets to ya.
http://gilana.org
sy_gilana is online now   Reply With Quote
Old 16-01-2018, 11:27   #10
Registered User

Join Date: Sep 2017
Posts: 593
Re: Electronic Gurus please step up.

I think the dual shottky diode modules (D9, D10) simply clamp the input to the opamp between +5V and 0V, which protects the input from spikes and harmful excursions. I think I'm missing something regarding the sensor high/low waveform values.

The other unknown looks like an additional resistor (and diode) in the new Furuno sensor module that probably acts as a pull-up. This does not appear on the old Raymarine sensor module, as the zener from +V acts as a pull-up. Long-story-short, selecting a 5.1V zener to connect the new signal line to the +V supply may not give the exact voltage drop that you need. The other unknown is whether or not the new hall effect IC is the same as the old. If you could get the new resistor value, and the part numbers of the ICs, you could probably do a circuit equation to pick the perfect zener.

OR, you could just go sailing and try various zeners (a few pennies each) on clip leads until the speed indicates.

Alternatively, I'd be happy to put a scope on it if we could get someone to snorkel down and spin the wheel... that is if you happen to be in the Los Angeles area.
cyan is online now   Reply With Quote
Old 18-04-2018, 18:42   #11
Registered User
 
sy_gilana's Avatar

Join Date: Jan 2005
Location: On board
Boat: Van de Stadt 50'
Posts: 1,207
Send a message via Skype™ to sy_gilana
Re: Electronic Gurus please step up.

Well, haul out time has arrived. We are up on the hard stuff, and have been for a week. Today I pulled the old transducer out, tomorrow the new one goes in. I will try to take apart the old one, and see the value of the Zener inside there. The potting stuff is incredibly tough. I might have to burn it out, unless someone has a better idea.

I will revert with my findings.
__________________
Tight sheets to ya.
http://gilana.org
sy_gilana is online now   Reply With Quote
Old 19-04-2018, 16:18   #12
Registered User
 
sy_gilana's Avatar

Join Date: Jan 2005
Location: On board
Boat: Van de Stadt 50'
Posts: 1,207
Send a message via Skype™ to sy_gilana
Re: Electronic Gurus please step up.

Today I tore down the transducer. Dang that rubbery stuff is tough, but not tough enough to stop water getting inside, which explains the failure. I am surprised.

I carefully cut away slivers of the compound to find the components, I found and identified:
The Ceramic Piezo element
The Hall Effect IC, with number S71436
A capacitor, blue 220 Microfarad
A capacitor, yellow with 100, I suspect 100 Picofarad.
I did not find the Zener, but there was a lot of water damage. I found a thing that could be the inner part of the Zener, it looks like a semiconductor.

The case continues.
__________________
Tight sheets to ya.
http://gilana.org
sy_gilana is online now   Reply With Quote
Old 15-05-2018, 18:46   #13
Registered User
 
sy_gilana's Avatar

Join Date: Jan 2005
Location: On board
Boat: Van de Stadt 50'
Posts: 1,207
Send a message via Skype™ to sy_gilana
Re: Electronic Gurus please step up.

Well, it looks like this has all come to naught.

I think we were on the right track, I finally hooked up the new Furuno tranducer, and armed with a selection of zener diodes, powered up the system.

Nothing...(apart from the sounder trying to work) the temperature and the speed were not working.

I then measured the power output from the display unit to the tranducer, and instead of getting 10.x Volts, there was....Nothing.

When I stripped the old transducer down to find the value of the zener, it was full of salt water. Clearly that fried the output side of my display head.

I don't have time to fix that now, and might never have. So if you were following this to see if it would work, I am sorry to say I have not got an answer for you.

Maybe time to look at eBay.
__________________
Tight sheets to ya.
http://gilana.org
sy_gilana is online now   Reply With Quote
Old 19-05-2018, 11:39   #14
Registered User

Join Date: Sep 2017
Posts: 593
Re: Electronic Gurus please step up.

Quote:
Originally Posted by sy_gilana View Post
Well, it looks like this has all come to naught.

I think we were on the right track, I finally hooked up the new Furuno tranducer, and armed with a selection of zener diodes, powered up the system.

Nothing...(apart from the sounder trying to work) the temperature and the speed were not working.

I then measured the power output from the display unit to the tranducer, and instead of getting 10.x Volts, there was....Nothing.

When I stripped the old transducer down to find the value of the zener, it was full of salt water. Clearly that fried the output side of my display head.

I don't have time to fix that now, and might never have. So if you were following this to see if it would work, I am sorry to say I have not got an answer for you.

Maybe time to look at eBay.
Oh well, thanks for the wrap-up. Darn salt water! (oh, wait, we need that stuff the sail upon)
__________________

cyan is online now   Reply With Quote
Reply

Tags
lease

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Want To Buy: Up-N-Out 4-Step Inflatable - Wide Step dinghy ladder rgesner Classifieds Archive 3 04-10-2015 16:46
Step 1: convince wife. Step 2.....? ontherocks83 Atlantic & the Caribbean 0 23-07-2015 09:58
For Sale: Brushing Awlgrip — A Step by Step Video Guide dennisjay Classifieds Archive 2 17-05-2011 11:54
Step-by-Step - for Dummies . . . Jimbo2010 OpenCPN 7 30-09-2010 18:43



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 19:16.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2018, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2018, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.