• Announcements

    • Zapata

      Abbreviated rules   07/28/2017

      Underdawg did an excellent job of explaining the rules.  Here's the simplified version: Don't insinuate Pedo.  Warning and or timeout for a first offense.  PermaFlick for any subsequent offenses Don't out members.  See above for penalties.  Caveat:  if you have ever used your own real name or personal information here on the forums since, like, ever - it doesn't count and you are fair game. If you see spam posts, report it to the mods.  We do not hang out in every thread 24/7 If you see any of the above, report it to the mods by hitting the Report button in the offending post.   We do not take action for foul language, off-subject content, or abusive behavior unless it escalates to persistent stalking.  There may be times that we might warn someone or flick someone for something particularly egregious.  There is no standard, we will know it when we see it.  If you continually report things that do not fall into rules #1 or 2 above, you may very well get a timeout yourself for annoying the Mods with repeated whining.  Use your best judgement. Warnings, timeouts, suspensions and flicks are arbitrary and capricious.  Deal with it.  Welcome to anarchy.   If you are a newbie, there are unwritten rules to adhere to.  They will be explained to you soon enough.  
allene222

Can I input a 5 volt pulse train into a TackTick speed hull interface input?

Recommended Posts

I have a Tacktick system and right now am bypassing the speed portion of the hull interface.  The Airmar speed sender is powered by a steady 5 volts and the output goes to an Arduino based interface I built.  I would like to hook up the speed pulse train to the Tacktick hull interface so I can compare the standard Tacktick speed readings to the other stuff I am doing but I don't want to burn out the hull interface so I am wondering if anyone knows if this will work.

Share this post


Link to post
Share on other sites

Your TackTick interface should be robust enough to tolerate ESD from handling and some level of applied signal. If you are concerned about burning it out, put a resistor in series to limit the current. A 10k might be a good starting point. but if you don't have documentation, start at 1Meg and work downwards until you get a reasonable signal. 

Share this post


Link to post
Share on other sites
11 minutes ago, LionessRacing said:

Your TackTick interface should be robust enough to tolerate ESD from handling and some level of applied signal. If you are concerned about burning it out, put a resistor in series to limit the current. A 10k might be a good starting point. but if you don't have documentation, start at 1Meg and work downwards until you get a reasonable signal. 

Yeah, I was going to try 10k but I think stating high is a better idea.  Hard to see that 1/2 mA is going to damage anything.  My larger concern is that the signal applied to the V+ line to the sender is somehow part of the reading or that the reading depends on some characteristic of the sender other than just a voltage.  The waveforms under normal hookup are very strange.

Share this post


Link to post
Share on other sites

If the Airmar is a magnet/coil pulse then it's going to look somewhat weird. Might approach sinusoidal if the impedance it drives is high enough. 

loading down it will add drag to the sensor and make your low speed even worse accuracy

 

Share this post


Link to post
Share on other sites

It is a hall effect sender.  The strange waveforms look like they come from the V+ signal being a pulse train driving the capacitor so the supply voltage decays over time. Also the signal into the interface drops about half way through it each pulse.  I assume this is due to some hysterysis.

Share this post


Link to post
Share on other sites

Hall effect is just modulation of resistor in a magnetic field.

They may include some network to generate pulse from a comparator, perhaps a 555 running as a oneshot. 

(maybe something like this: http://www.dummies.com/programming/electronics/components/electronics-components-555-timer-chip-in-monostable-one-shot-mode/

Share this post


Link to post
Share on other sites

What is strange (unique) about the TackTick is that it can run on battery power so the +12 input is not required.  It seems that they did some tricks to make that happen and I think the odd waveforms are a direct consequence of that.  My guess is that they inject enough charge into the Airmar to keep it running off its internal capacitor and have a comparator on the input with some hysteresis and I will be fine just presenting a square wave but I was looking at the long shot that someone had done this. Some series resistance is obviously a good idea to mimic the source resistance of the Airmar, whatever that is.

Share this post


Link to post
Share on other sites

The result is that this does work but there were some "interesting" discoveries along the way.  Basically, the normal output of the speed sender must be received in the hull transmitter knowing the drive voltage as the noise is pretty much indistinguishable from the signal.  This explains why my comparator that just tapped onto the log output had so much noise on it.  When driven by a clean 5 volts, the output of the speed sender is clean as can be.  Taking that output and inputting it to the hull transmitter with either a 100k or 10k resistor in series worked so I used 10k.  I measured the output resistance of the speed transducer as either 600 ohms or infinity depending on polarization and either the 100k or 10k resistor dropped 1/2 a volt so the circuits here cannot be modeled with simple resistors.  But no matter, it worked.

The one "interesting" thing that cost me an hour was that the hull transmitter speed only works if the temperature wires are connected.  I did not initially hook them up because my depth unit outputs NMEA temperature data.  But with everything hooked up, I now have the standard Tacktick speed working as well as my Arduino unit that averages the port and starboard senders.

PS,  If you are counting wires, the Arduino unit has two speed sender inputs on the left, a NMEA output on the lower right, and a NMEA input on the upper right.  The unit takes the depth input and multiplexes it with speed so that my RaceBox and get the depth readings without an additional NMEA input.

 

speed.jpg

Share this post


Link to post
Share on other sites

Interesting. I have wondered why you found your tackticks have been so poor for speed when I have had no problems over 7 years of use, checked with regular calibrations. I just figured your much greater technical know-how was detecting problems that I couldn't see :)  But I did discover the system was flaky without the temperature wires a long time ago when fiddling around putting in a second paddlewheel so I have one in each hull of my catamaran, but I forgot about it til I saw your post! 

Share this post


Link to post
Share on other sites
1 hour ago, Peccadillo said:

Interesting. I have wondered why you found your tackticks have been so poor for speed when I have had no problems over 7 years of use, checked with regular calibrations. I just figured your much greater technical know-how was detecting problems that I couldn't see :)  But I did discover the system was flaky without the temperature wires a long time ago when fiddling around putting in a second paddlewheel so I have one in each hull of my catamaran, but I forgot about it til I saw your post! 

Poor is a relative term.  The tacktick by itself has been solid but has two attributes I did not like. One is that it just does not display any reading below 1.3 knots.  Second is that it has about twice the noise for a given filtering compared to the Signet.  The Moor unit I had before had even less noise than the Signet as its paddle wheel was even larger.  The issue I had that led me to power them off 5 volts had to do with my trying to sniff the signal for my Arduino unit.  Did a test yesterday and everything is working as it should.  

Interestingly, with the averaging of the Tacktick and the Signet, the total noise is about the same as the Signet alone because the signal is larger with adding the two readings and the noise is uncorrelated so doesn't add up as much.  The temperature sender reading was only an issue for an hour during my conversion to the clean 5 volt drive.

Share this post


Link to post
Share on other sites

I just came in from a test and I did see 1.2 knots on a slow coast.  Next reading was zero. Maybe they changed the software when RM bought them.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now