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Positive earth speed sensor?

Discussion in 'Norton Commando Motorcycles (Classic)' started by click, Jul 31, 2019.

  1. click

    click VIP MEMBER

    Joined:
    Dec 27, 2008
    Hi,

    I'm looking at fitting one of the classic electronic Smiths speedo's.

    I want to eliminate the mechanical gearbox drive & I'm not keen on the GPS solution so . . . . . .

    Ideally I need to use a sensor BUT my bike has still got the original positive earth system.

    Does anybody know of a sensor which will work with a positive earth system?
     
  2. maylar

    maylar VIP MEMBER

    Joined:
    May 13, 2007
    Smiths' sensors work with either earth polarity.
     
  3. kommando

    kommando

    Joined:
    May 7, 2005
    As long as they do not earth to a metal surround modern electronics can be wired either way.
     
  4. click

    click VIP MEMBER

    Joined:
    Dec 27, 2008

    Interesting, my understanding is that you have two options with the new Smiths electronic speedo's, run them off the original mechanical drive using a sensor that screws in like the old speedo cable or use a GPS signal cable.

    Are you saying there's a third option?
     
  5. Ibex

    Ibex

    Joined:
    Jul 31, 2013
    Magnetic pickup. I fitted 2 magnets (but 1 will do) onto the aluminium rear wheel hub cover and made a bracket for the pickup unit (see 'digital speedo' site or 'Puca' site. Bracket is bolted onto the very convenient slot under the spindle (1974 Mk2) which allows for re-adjustment when chain adjusted.
     
  6. click

    click VIP MEMBER

    Joined:
    Dec 27, 2008
    I have a very basic understaning of electrics. This would mean isolating the sensor from a metal mount i.e. rubber mounting it.

    Have I got this right?
     
  7. Ibex

    Ibex

    Joined:
    Jul 31, 2013
    If you use the magnetic pickup it has 2 wires coming from it to connect to the speedo, fit either way because the sender is not polarity sensitive. Wiring speedo can be done for positive or negative earth as in the (confusing) wiring instructions supplied.
     
    jan nelder likes this.
  8. texasSlick

    texasSlick VIP MEMBER

    Joined:
    Jan 2, 2013
    If the sensor has two wires, and neither wire is connected to the metal sensor frame, then, as Kommando says, the sensor can be wired either way.

    If the sensor has one wire, and if the earth connection is intended to be made by mounting to a negative earth system, then you are right....... electrically isolate sensor, connect the one wire to positive (+), then attach a second wire to the metal frame of the sensor and connect this wire to negative (-).

    Slick
     
  9. kommando

    kommando

    Joined:
    May 7, 2005
    Take a multi meter set to ohms and probe the wire ends and the body, both will be infinity as they are isolated from the body internally.
     
  10. texasSlick

    texasSlick VIP MEMBER

    Joined:
    Jan 2, 2013
    Switch the meter lead wires around and do this test again. A reading of infinity should ALWAYS occur if the lead wires are isolated from the sensor metal body.

    Example .... meter red lead wire on body ..... check both sensor wires .....> infinity
    Switch ........ meter black wire on body ...... check both sensor wires .......> infinity

    Slick
     
  11. click

    click VIP MEMBER

    Joined:
    Dec 27, 2008
    OK, I'm just about keeping up with you guys!!

    I'll explain a little bit more, I was in touch with Matt in CNW, he has enough 'bits' to make up a 'kit' which will replace the mechanical speedo drive when fitting one of the new Smiths electronic speedo's using a sensor.

    He has never fitted this setup to a positive earth system, he was kind enough to test the system for me on a postive earth & said it did not work, he uses a 3 wire sensor.
    There might be more to this than my explination but it's my understanding of what Matt did.

    So, I thought I'd ask if you can get a negative earth sensor to replace the one Matt supplies.

    Not sure if that changes any of the helpful comments above?
     
    Last edited: Jul 31, 2019
  12. tomspro

    tomspro VIP MEMBER

    Joined:
    Jan 25, 2014
    I am using the magnetic pickup supplied by Smiths on a positive ground bike. Would work on negative ground systems too.
    It uses two wires - not clear what Matt is using.
    First item on this page:
    https://smithsgaugesusa.com/accessories/
     
  13. click

    click VIP MEMBER

    Joined:
    Dec 27, 2008
    Appreciate the info. I just checked the http://www.puca.co/tech.html site which is much better than the Smiths UK site! Are you using the M8 reed-switch sender and M6 magnetic bolt they supply? Did you mount the sensor on the front or rear wheel?
     
  14. Fast Eddie

    Fast Eddie VIP MEMBER

    Joined:
    Oct 4, 2013
    This is my set up:

    Plain large nut from Matt (no ‘dimples’ as per his standard one), machined to take one magnet (can use more, but one works fine).

    Matts speedo sensor holder.

    Puca Smiths m8 pic up.

    I had to machine an eccentric bush for the pic up as A) the hole is too big and B) align it perfectly with the magnet.

    Bike is positive earth.

    Very easy. Works perfectly. Very neat set up.



    B8C6E7BB-2D6A-4DC4-859A-22091188EAD9.jpeg C564E688-F0E6-4FF8-849B-E68843515A92.jpeg
     
    MichaelB likes this.
  15. click

    click VIP MEMBER

    Joined:
    Dec 27, 2008
    Bingo! That’s the setup I’m looking for.

    The nut Matt supplies with the dimples must be for use by a different type of sensor, not magnetic?

    I’ll see if Matt can supply the plain nut. Did you machine the nut to take a magnet or Matt?
     
  16. tomspro

    tomspro VIP MEMBER

    Joined:
    Jan 25, 2014
    No, on puca page it is listed as for Honda and Triumph.
    I glued a ceramic magnet onto my rear brake drum and attached the sensor to inside of chainguard.
     
  17. jbruney

    jbruney

    Joined:
    Jan 5, 2019
    Eddie I don't understand how your Commando runs because there appears to be no oil, grease, or grime to permit your bike to pass through the atmosphere which is fairly dense near sea level.
     
  18. Fast Eddie

    Fast Eddie VIP MEMBER

    Joined:
    Oct 4, 2013
    Matts dimples (triggers) are none magnetic and his pick up is magnetic. You have to do it the other way around.

    I drilled the nut and fitted the magnet myself. Asked Matt for a ‘special’ none dimpled nut.
     
  19. Fast Eddie

    Fast Eddie VIP MEMBER

    Joined:
    Oct 4, 2013
    The bike is so fast dirt can’t stick to it...:rolleyes:
     
    MichaelB likes this.
  20. jbruney

    jbruney

    Joined:
    Jan 5, 2019
    Mine must be awful slow then because everything sticks to it.....including seagull crap, which is donated on a regular basis. Reminds me of an old time whorehouse...scrub it before you ride it.
     
    jan nelder likes this.

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