How make a pulse multiplier or divider?

Discussion in 'The Projects Forum' started by Jack_K, Jan 27, 2010.

  1. Jack_K

    Thread Starter Active Member

    May 13, 2009
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    I have a motorcycle that I added and extra speedometer. The speed read far too low, so I bought a device called a SpeedoHealer. This thing lets you set the speed ratio to +/- about 200% of the input pulse rate. It works great. My speedo is very accurate now.

    It got me wondering how they might have done that. There is a single IC that I assume is probably a PIC. There's a 2-digit LED display that displays the selected ratio and a push button switch for setting the ratio.

    Any thoughts on how it works? I'm not asking for a schematic, that would be fairly simple, just an idea how the code would work.

    Jack
     
  2. SgtWookie

    Expert

    Jul 17, 2007
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    What is the part number on the IC? Microchip PIC uC's all start with PIC, obviously.

    They might just be letting a timer free-run at the CPU clock speed, averaging out a few samples of the clock counts between input pulses, and then using a PWM output that matches your multiply or divide requirement, or just generating that output in software.
     
  3. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Its either a simple counter (frequency divider), a special counter called a "binary rate multiplier", or a Phase Locked Loop with two counters m/n. It may be done inside a PIC, but its still one of the above ;)
     
  4. Jack_K

    Thread Starter Active Member

    May 13, 2009
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    What is the part number on the IC?

    It's been buffed off.
     
  5. THE_RB

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  6. Jack_K

    Thread Starter Active Member

    May 13, 2009
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    Thanks for the ad but it won't work for me. It will correct to +100% and my speedo needed 225% since it read about 27 MPH when my GPS showed my speed as 60 MPH. I never could have gotten there with the yellow thing.

    Jack
     
  7. hgmjr

    Moderator

    Jan 28, 2005
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    Another technique for accomplishing this would be to use a frequency-to-voltage converter the output of which feeds an opamp gain stage then the output of the opamp would feed a voltage-to-frequency converter. The multiplication factor would be adjusted by changing the gain of the opamp.

    hgmjr
     
  8. Jack_K

    Thread Starter Active Member

    May 13, 2009
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    Sounds interesting. Any suggestions on ICs?
     
  9. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    Sorry my mistake, I didnt realise you needed such a large correction.

    What vehicle is this for? Or is it one of those kit cars?
     
  10. Jack_K

    Thread Starter Active Member

    May 13, 2009
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    I put a Harley Davidson tachometer on my Yamaha Stratoliner.

    [edit] Sorry, speedometer.
     
  11. Jack_K

    Thread Starter Active Member

    May 13, 2009
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    I put a Harley Davidson speedometer on my Yamaha Stratoliner.
     
  12. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    Ahh ok, thanks for the info.

    You do know many of the custom Harley speedos have recalibrate function built in so you don't need a recalibrator?

    Or if you must use the speedo you have, why not stick with the reclibrator you already purchased?? It's not a trivial application to make one, especially considering the speed conversion has to be accurate enough to be legal.
     
  13. Jack_K

    Thread Starter Active Member

    May 13, 2009
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    I'm using the one I bought. It just made me curious about how it works. I thought it would be fun to try to make one.

    Jack
     
  14. Jack_K

    Thread Starter Active Member

    May 13, 2009
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    No more ideas on how to do this? I've been thinking about software but that seems too complicated. There MUST be a hardware chip that can do this, otherwise it must be software.

    Jack
     
  15. Jack_K

    Thread Starter Active Member

    May 13, 2009
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    Here's my idea for software to do this. Count the number of pulses emitted by the VSS in a 100 ms window. Multiply that number by user's input. Send new number of pulses in a 100 ms window. repeat.

    I suspect the speedometer would not mind getting pulses only half the time since half would be only 0.1 second.

    Here's my flow chart.

    Jack
     
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