Motor cycle tacho or RPM meter

Discussion in 'General Electronics Chat' started by R!f@@, Jan 30, 2014.

  1. R!f@@

    Thread Starter AAC Fanatic!

    Apr 2, 2009
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    This is not by any chance auto motive modification even though you dunno what I had in mind. :D

    Having said tht, I was wondering about this idea last night.
    I wanted to read the engine RPM without taping into the harness.

    I believe I can take the pulse by placing a coil on the spark plug wire.

    The high voltage can induce enough voltage in the coil to make a pulse each time the coil generates a pulse, right ?

    Question is what is the pulse count for a 4 stroke engine.

    How many pulses would be produced by one engine rotation?
     
  2. Dr.killjoy

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    Apr 28, 2013
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    Yeah thats how a timing gun works ...Also I help more when I can get home ( diesal work truck was never plugged in last night amd now won't start) ...I would look up a timing light curcuit and work from there..
     
  3. R!f@@

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    I am planning to cook up something to make a LED ( like say 50 SMD LED's ) to ramp with the engine u know.

    I am not targeting this for diesel. It's a Petrol type motor cycle. And I think it is 4 stroke.
     
  4. Dr.killjoy

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    I figured that and most bikes are gas ...But I am stuck a work because my diesel won't start ..
     
  5. R!f@@

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    Ur diesel or your car or truck ?
     
  6. Dr.killjoy

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    I drive a tow truck which is a turbo diesel but with it being cold it won't start..
     
  7. inwo

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    Nov 7, 2013
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    One or 1/2 per rev..;)

    Many small engines use wasted spark system.

    Self powered clip on modules are common, and commercially available.
     
  8. alfacliff

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    Dec 13, 2013
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    a one cylinder four stroke engine pulses at half the rpm. a two cylinder might pulse once per rpm, or half rpm depending on the ignition design. a three will ulse each plug at half rpm, a 4 cylinder will act like a two cylinder, once or half per rpm.
    the "wasted spark " system uses only one set of points or pickup for two cylinders, firing both at the same time, one into a closed cylinder and one into a cylinder on exhaust, makes the ignition cheaper.
     
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  9. R!f@@

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    Crap !!

    I need to find more abt the darn engine.
     
  10. inwo

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  11. alfacliff

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    my old xs650 yamaha had two different ignition timing systems on the olderones, they had to sets of points, the newer ones had one, or one magnetic pickup for both cylinders.
    Mhy 06 Triumph bonnieville has both plugs fire at the same time, the scrambler model fires seperatley.
    find aftermarket tachs are ususally switchable to match the engine.
     
  12. tracecom

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  13. inwo

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    I think that's what I have on one of my small engines.:eek:
    Couldn't find a name.
     
  14. R!f@@

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    One does not ship to Maldives other too much money.

    I am going to make one.

    Should I count the pulses or should I use an integrator and use the ramp to scale the LED's
    Which will be easier ?

    I am thinking of making a proto and see what works best.

    The final will be I think in the same uC tht I have planned to program and mix with some other stuff.
    Still I am not sure on what else I have in mind.

    confusing, ain't it ?

    PS.. I believe there is a sensor to count the engine pulses cause the KM meter is a digital one. The meter uses two coils and is analog in display. The coils are driven by the uC in the meter.
     
  15. ian field

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    Oct 27, 2012
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    Apparently what used to be Royal Enfield made a diesel motorcycle - as its now an Indian company they're not permitted to use Royal in the name, I think its something like Madras Enfield now.
     
  16. GopherT

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    Nov 23, 2012
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    We still haven't heard if 1,2,3 or 4 cylinder engine you are working on. The only difficulty was if vertical twin or Beemer twin, you may have one firing every rev or every second rev. To find out, look how many ignition coils you have. That is, do both spark plug wires go to the same little box or two separate boxes. If you don't have referenced motor, then no worries. My as well check if you have a v-twin also. Engines like vx800 (intruder), have off-set crank pins so a single coils is possible there too.

    Next is how best to measure RPM with Microcontroller. I always liked the idea of a running sum integration. That is, 60 seconds in a minute so count revs in 0.6 seconds. Display as x100 for RPM. 8 sparks, 800 rpms. 100 sparks, 10000 rpm.

    If you want, you can measure every 0.06 seconds, and add the previous 9 readings to the new reading (10 total). That way it updates more frequently be put is smooth enough to read it.
     
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  17. R!f@@

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    Heee heee ! V twin engines...! Like I have tht. In my dreams tht is

    OK. Lemme refresh what I saw when I overhauled my motor cycle. I remember it has one spark plug and one coil and one piston. whole lotta gears and a clutch mach, automatic tht is and one alternator. It has a tacho at the pin wheel( is tht what you call the small spike type wheel that couples the chain to the big spike wheel thingy screwed to the back wheel hub.) That tacho senses tht RPM and the meter pointer rises only when it spins. The Hr meter goes up when it runs forward and down when it rotates the other way. ( tht is the best part, I can reduce the engine run time tht way ).

    I was thinking of letting go the uC and use some SMD LM3914 types to scale the LED or would it be wiser to use a uC.
     
  18. shortbus

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    Sep 30, 2009
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    Why not use the connection to the primary side of the coil and be done with it? This is how most original equipment and aftermarket tachs were driven, at least before cars/bikes started using an ECM.


    And those "spike thingys" are called sprockets. :)
     
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  19. R!f@@

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    Heeeeey! U want this thread closed. No tampering to harness. U are drifting into enemy territory. :eek:


    Darn ! I knew tht before. Somehow I 4got as I was typing. :(
     
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  20. alfacliff

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    Dec 13, 2013
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    sounds like a one cylinder engine, now is it a two or four stroke engine? four strokes fire once every other rev, two strokes fire every rev.
     
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