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Frequency Doubler.

  1. Feb 26, 2009 #1

    I hope someone can help... Basically, I own a 2000 Ford Mondeo 1.6, and my speedo is reading half of my actual speed. Now we've got it down to something inside the gearbox.

    So, I now need to bring my speedo up - And the only method I can think of using is a frequency doubler.

    I've come across this PDF: http://www.wenzel.com/pdffiles1/pdfs/diodedbl.pdf [Broken]

    I don't suppose anyone here can make better sense of what I need ?

    The frequency doubler will need to be put on the wire for the VSS (Vehicle Speed Sensor)

    Thanks alot,
    Ferret !
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Feb 27, 2009 #2


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    So some things about this vehicle have been changed out and you have a compatibility issue? What type of sensor is in the gear box? How many wires are coming from it?
  4. Feb 27, 2009 #3
    I'm not too sure on the circumstances surrounding how this has happened - I bought the car with this problem, cheap !

    But like I say, I know for a fact that it's something inside the gearbox - Nothing to do with the sensor, or any wiring.

    It has 3 wires coming off the sensor.

    Ferret !
  5. Feb 27, 2009 #4


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    Ok. It is most likely a hall effect sensor. 3 wires would be: Power, ground, and signal. Does it look like a botched up job of some sort? Do things look 'put together'? I would guess that someone has swapped out the transmission. What happens if you disconnect the speed sensor? Is the speedometer the only thing that quits working? What I am getting at here, is that if you would double the frequency will it affect anything besides the speedometer? If it truly is a tranny sway that is causing it, then doubling the frequency should put everything back the way it is supposed to be.
  6. Feb 27, 2009 #5
    Is your odometer working correctly?
  7. Feb 27, 2009 #6


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    Are there odometers that have half the sampling frequency? Or is this likely to be something like a magnet falling off on some wheel that a Hall Effect sensor is monitoring?
  8. Feb 27, 2009 #7


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    Generally automotive sensors will not have a magnet attached to a wheel. The sensor will have a magnet built in and use whatever moves past the sensor as a reluctor.
  9. Feb 27, 2009 #8
    supernova is correct, the sensor has the magnet built in !

    And no, the mile counter isn't working correctly - Again, it's about half of the mileage i'm doing !

    Also, the VSS sensor has not been botched on. It's possible that the gearbox has been put on, and it's the wrong one, but I really don't think they've done that !

    When I disconnect the VSS, it's only the speedo that stop's working - The rev counter works off the crank sensor.
    Some cars rely on the VSS sensor heavily... Mine only relys on it for 2 things, 1 the speedo, and 2 the MPG calculator. So I have no running issue's - It's just annoying not knowing the speed i'm actually doing !

    So do I have to make a circuit board for the frequency doubler, or is it as simple as just solder in a diode on the wire ?

  10. Feb 27, 2009 #9
    on older vehicles with mechanical speedos, you could just swap out the gear where the cable connects to the trans. Steeda and other companies would sell different ratios for people with aftermarket tires/trans/diff. i would look around and see if there is a similar fix for vehicles that use an electrical pickup.
  11. Feb 27, 2009 #10


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    Contact these guys:

    http://www.dakotadigital.com/index.cfm/page/ptype=product/product_id=126/category_id=287/home_id=59/mode=prod/prd126.htm" [Broken]
    It is unlikely that the circuits you provided would help you much. Most hall sensors used in automotive have an open collector output. To the lesser informed that means that there is a switch that opens and closes to ground. So if you build something, you need a bit more than a diode/transformer frequency doubler. If you truly bought the vehicle cheap, the small cost of a module from the link I provided won't hurt you much.
    Last edited by a moderator: May 4, 2017
  12. Feb 27, 2009 #11
    That thing is kinda what i'm after, not a bad price either.

    I'd prefer to find one in the UK though (thats where i'm from).

    I was just hoping to build one myself.

    Ferret !
  13. Feb 28, 2009 #12
    My car reads 12% fast. I'm told it's because the gear-pair is the wrong set for the rear-end.
  14. Feb 28, 2009 #13
    Mines reading about 50% slow - And it's alot easier to build a frequency doubler, than to take the gearbox off.
  15. Feb 28, 2009 #14
    A CMOS 4046 might do the job. But we don't know what the goes-in-tas and goes-out-tas are.
  16. Feb 28, 2009 #15


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    4046 or any PLL is not going to do the job. Consider the frequency range that needs to be covered. Oscillators typically cannot cover the range required here.
  17. Feb 28, 2009 #16
    Is the odometer also reading half as much?

    Rather than assume the pulse rate is wrong, it could be that the electronics is blown.
    Last edited: Mar 1, 2009
  18. Mar 1, 2009 #17
    Phrak - It is the pulse rate thats wrong... i've bypassed the wiring in the car, and directly wired another set on clocks straight onto the VSS, and still got the same results !
  19. Mar 1, 2009 #18
    OK. There's not a lot to go on without knowing what the signal coming out of the gearbox looks like. If it's a pulse that goes from about ground to +12volts, this might do it.


    10nF*10K ~ 100 microsecond plus width. The pulse width should be about half the pulse width coming out of the gear box at maxium speed or it won't work. Adjust the component values accordingly. It's cheap and dirty, but may serve...
    Last edited by a moderator: Apr 24, 2017
  20. Mar 1, 2009 #19


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    Consider the range of frequencies that need to be covered here. From 5-10 KPH to well over 100. I don't think pulse forming will work over that complete range reliably. Trust me, the unit in the link I provided works. There is a good reason I know this. :wink:
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