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Topic: Motorcycle Tachometer help (Read 3 times) previous topic - next topic

RobDrizzle

I'm trying to make a gauge cluster for my older motorcycle. I was going to use a hall effect with a magnet on the timing wheel (a wheel that spins 1RPM per 1 engine RPM) but as soon as I turned the engine on the hall effect went nuts. The ignition coils and spark plugs are causing a lot of noise!

Here is the hall effect sensor I was using.

http://www.adafruit.com/products/158

Is there a way to clean the signal up? Is there a better hall effect to use?

Finally, I know there is another way to detect RPM based on an inductive pick-up on the spark plug wire. I have read that you can use an LM395 with the wire wrapped around the spark plug wire and then connected to the base of the transistor. But that is all the details I got. Can someone shed some light as to how I can try this?

-Rob

MarkT

You have to use full screening to prevent the interference (and even that may not be enough).  So find a cable with two of more wires inside a braided screen - the screen is connected to Arduino ground (do NOT connect to the vehicle chassis except via the Arduino, or you'll have a ground loop).  At the hall-sensor end keep the wiring that's outside of the screen as short as possible.

This ought to reduce the pickup you've been experiencing a lot...  Remember your HT leads are carrying a 30kV signal so even tiny amounts of stray capacitance will inject a lot of signal into nearby wiring unless its screened.  For some stupid reason the HT leads on an engine are not themselves screened (which would be an obviously better solution).
[ I won't respond to messages, use the forum please ]

deaurgtehne

Excuse my ignorance, but why not use a Reed switch? Which is what I am currently doing.

RobDrizzle

Well, I guess a reed switch is an option, but I can think of a few problems with the reed switch also.

1) vibration from being mounted on a high revving motorcycle engine may cause it to close without a magnetic field.
2) the need for debounce could slow the code and response.
3) the speed that it would need to open and close would be on a magnitude of 200 times/sec, I don't know if it can react that quick.

If the hall effect doesn't work I'll probably move on to an inductive pickup.

dc42

As well as using shielded cable to connect the Hall sensor, reducing the value of the pullup resistor to +5v will help make the circuit less sensitive to noise. I would use 220 ohms.
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

RobDrizzle

Ooooo... good idea, currently I'm using a 10k which in this application, is very weak.

RobDrizzle

Stronger pull-up and shielded wire helped only a little... Still pretty noisy.

Any other things to try?

dc42

Here are some further suggestions:

1. How do you have the grounds connected? For best noise immunity, designate one of the Arduino pins as signal ground. Use it only to connect the ground side of the Hall sensor and the shield of the shielded cable. Use the other ground pin to supply power and for any output devices.

2. I presume you are powering the Arduino by feeding +12v from the motorcycle battery into either Vin or the barrel jack. The problem could possibly be caused by noise on the 12v line. You can check this by temporarily running the Arduino from a 9v battery and seeing if it is any better.

3. Keep all the wiring away from the HT leads.

4. If you post photos of your setup, they may make is easier for me and others to diagnose the problem. It would also be helpful to know what sort of shielded cable you are using and how you have it connected.
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

dc42

PS - is the sensor itself well away from the HT leads and ignition coil?

If all else fails you could try a R-C filter on the input pin. Something like 1K between the pullup/hall sensor and and the pin, and 10nF or 100nF from the pin to signal ground. But this should not be necessary if your sensor uses shielded wire and is correctly grounded
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

deaurgtehne

What?! where do you want to mount the reed-switch?

I am mounting it on my shock, and I have a magnet expoxy'ed into my break disc caliper... I suppose you guys all ride superbikes where that makes a difference... (me : XR650L, KTM950SE)

RobDrizzle


PS - is the sensor itself well away from the HT leads and ignition coil?

If all else fails you could try a R-C filter on the input pin. Something like 1K between the pullup/hall sensor and and the pin, and 10nF or 100nF from the pin to signal ground. But this should not be necessary if your sensor uses shielded wire and is correctly grounded


I don't have any pictures of the setup but I can tell you that I did exactly as you said with the shielding, I grounded the shield (tied to the hall effect ground) to the UNO. I'm using a 4 conductor shielded wire and power and signal are protected by the shield. I kept the bare wires short (less than 1")

For now the hall effect is the only thing close to the bike, the crank position wheel (where the hall effect is) is about 12" below any HT wires. The shielded wiring is running along the floor, 5' away to the uno and computer resting on my tractor (lol), The uno is powered by the computer. There is no power being shared from the bike. The signal wire is 12" or more from any HT wiring.

There is a problem inherent with wiring on a bike... sooner or later I will have to route the signal wiring to the dash area... which will pass by the coils and HT wiring within an 1"...  :(

RobDrizzle


What?! where do you want to mount the reed-switch?

I am mounting it on my shock, and I have a magnet expoxy'ed into my break disc caliper... I suppose you guys all ride superbikes where that makes a difference... (me : XR650L, KTM950SE)


You do know the difference between a tachometer and a speedometer, right?

deaurgtehne


You do know the difference between a tachometer and a speedometer, right?


Haha, my bad, for a moment I got super confused.  I am building both and typed without thinking :)

scootn405

#13
May 31, 2012, 10:00 pm Last Edit: May 31, 2012, 10:33 pm by scootn405 Reason: 1
I'm looking to make a digital tach for my scooter and my question is why not use the magnetic pickup on the stator or the points to mark the rotation? I have an electronic ignition and an trying to find a way to use the existing pickup.

Big D

This may be a dumb question but why couldn't you just connect a mosfet to the ignition coil signal (12v side) and have the arduino count the pulses? If it is a 4 stroke motor, 1 pulse = 2 revs?

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