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Topic: How do I get this tachometer signal readable? (Read 3757 times) previous topic - next topic

Beun

Oct 16, 2013, 03:17 pm Last Edit: Oct 19, 2013, 01:50 pm by Beun Reason: 1
Hi, I am new to arduino and I have a couple of questions regarding the possibilities of a motorcycle dashboard based on arduino.

My plan is to make a TFT or LCD dashboard with the following functions:
  • Tachometer

  • Speed/Odometer (also re-settable trip meter)

  • Engine temperature (sensor is present)

  • Time/Date

  • Fuel mixture gauge lean/rich

  • Battery voltage

  • Fuel warning light

  • Turn signal indicator


My two stroke supermoto has a high voltage output for a OEM tachometer, but I was wondering if a inductive sensor on the ignition cable would be a better alternative? For the speedometer I was thinking about a magnetic bolt in my disc brake and a magnetic relay on my fork, much like the bicycle speedometers. The fuel warning and the turn signal indicator are currently controlled by on/off switches/sensors, so I'm expecting no difficulties there.

The Fuel mixture gauge is an idea I got from the Scooterputer but I have not yet found out how this works, does anyone have an idea on how they did this?

As for the screen I was wondering what type of display has the best visibility with bright sunlight? I was thinking about a non-touch 240x320 2,4" back-lit TFT but suggestions are always welcome. I was also wondering how hard it would be to make the graphical interface, because i have only a little experience with programming/scripting.

And the final questions: what (major) parts do I need besides the arduino, the display and the clock? (I want to make a BOM for the costs) and which arduino board is the most suitable for my plans?

Thanks in advance, your help/suggestions are much appreciated! XD




PeterH

#1
Oct 17, 2013, 02:35 am Last Edit: Oct 17, 2013, 02:41 am by PeterH Reason: 1
In my experience, inductive couplings suck. Drive the tacho off the output designed for the purpose - or straight off the coil LT if the tacho is designed for that and you don't have any cleaner options.

Regarding the fuel mixture gauge - from the hardware involved it's evidently using a narrowband lambda sensor, and the only useful thing that will show you is that the AFRs are cycling healthily under closed loop control (i.e. rather than pegged) - the actual values it would show are effectively useless since in practical terms the sensor only outputs 'rich' or 'lean' and attempting to interpret that as a proportional AFR signal is futile. (You can buy aftermarket devices that claim to do it but they do not produce any meaningful output.)

Beun

Thanks for the reply.

After some more research I came to the following conclusions:
The fuel mixture gauge will be dropped. My exhaust is too valuable, I'm not going to modify it for sensors. Besides that it's too much effort for information that is not that relevant.

The clock, voltage meter, temp sensor, indicators and speedometer seem manageable to me, although I'm not an expert when it comes to electronics. However, the tacho seems like a real obstacle. I hooked up my multimeter to the signal wire for the tachometer and it seemed to pulse with 1,5 to 1,8 kV or so. Is there a (fairly) simple circuit that can convert this signal into arduino-readable format? or should I go for an alternative like a cable wrapped around my ignition cable?

PeterH


I hooked up my multimeter to the signal wire for the tachometer and it seemed to pulse with 1,5 to 1,8 kV or so. Is there a (fairly) simple circuit that can convert this signal into arduino-readable format? or should I go for an alternative like a cable wrapped around my ignition cable?


See if you can find out more detail about what sort of signal that is. If you really do mean KV (kilovolts) then that doesn't sound like a tacho output. You need to find out whether it's a digital signal or just a wire connected to something in the ignition circuit. If it's digital, you need to know how the RPM is encoded on it. If it's just a wired connection you need to know what it's connected to - the coil LT -ve is what's usually used for an analog tacho output but you need to know what you're dealing with before you can decide how to deal with it. As I said before, in my experience inductive pickups suck and I wouldn't recommend trying to pick up the spark signal inductively.

Beun

See if you can find out more detail about what sort of signal that is. If you really do mean KV (kilovolts) then that doesn't sound like a tacho output. You need to find out whether it's a digital signal or just a wire connected to something in the ignition circuit. If it's digital, you need to know how the RPM is encoded on it. If it's just a wired connection you need to know what it's connected to - the coil LT -ve is what's usually used for an analog tacho output but you need to know what you're dealing with before you can decide how to deal with it. As I said before, in my experience inductive pickups suck and I wouldn't recommend trying to pick up the spark signal inductively.


Yes, I really do mean kilovolts. I had to put the multimeter in HV mode to get a reading. It seems like a pulsing signal of some kind, but it's hard to tell since I don't have the right equipment to identify the signal and my engine isn't running yet (I used the kickstarter today while measuring the voltage).



This is the schematic of the electrical system in my two stroke bike. It's a negative ground and the yellow wire is the tacho signal (19 is the flywheel and 2 is the tachometer). I opened my broken tachometer and it uses a 12V line (red/black in the schematic), ground and the yellow signal wire. Inside the tacho is a small circuit and a motor that drives the needle.

should I post pictures of the pcb inside the tachometer?

Paul__B

A real circuit diagram.  That's amazing!

Could you point out what the other things are that the yellow wire goes to?

Running a wire around the vehicle loom, which carries kilovolt pulses sounds a bit odd but ...

It should be quite possible - as the tachometer clearly does (how did it break?) - to "condition" the signal to make it useful.  You need to trace out the actual circuit of the tachometer to get an idea.  Clearly it will involve some resistors in series with the voltage - a voltage divider in fact and it will be safer to have the high voltage part of this comprise say, four resistors in series - and a capacitor to smooth out the spark oscillations.

Beun


Could you point out what the other things are that the yellow wire goes to?


It's a voltage regulator (12V 80W DC according to the manual) and a turn indicator controller.

I also find that voltage odd, but its what my multimeter told me. Maybe I did something wrong? I'm not an expert on electronics, I'm more of a mechanic but I like to learn  :) I'll post some pictures of the circuit boards in the tacho tomorrow, maybe that will answer some questions.  I don't know how it broke, it was broken when I bought it, I've never had a working tachometer on my bike :(

Beun

#7
Oct 19, 2013, 01:49 pm Last Edit: Oct 19, 2013, 07:16 pm by Beun Reason: 1
Ok I made some photos and did some research on the components. I found this and this. I see a lot of resistors, diodes and capacitors but I don't know how this circuit processes the signal.

The top-right input is the tacho signal, bottom right is GND and bottom left is 12V, the other pin is not used. the 9-pin thingy at the top of the motor side says 9A332J, but I couldn't find any datasheets about it.
Picture 1
Picture 2
Picture 3

Any ideas on how to make this tacho signal arduino readable are  more than welcome

-EDIT- I measured the voltage on the signal wire again today. It turns out that my multimeter reads kilovolts when its close to the engine and not connected to anything, so there are no kilovolts on the signal wire.

Beun

A little update:

I measured the tacho signal line with without the spark plug. With a few ferocious kicks on the kickstarter the multimeter showed between 1 and 3 volts AC at fairly low rpm, so I'm guessing that the signal would be around 12V AC at high rpm. When I put the spark plug back in, I get kilovolt readings again. The ignition creates a lot of noise for some reason. 

I'm glad that the biggest problem turned out to be the noise on the multimeter and not the tacho signal.

Now I only have two questions left:

  • Shouldn't multimeters function normally around ingition systems? I've seen youtube videos with multimeters standing on top of a running engine and giving perfect readings. Is it my multimeter or my ignition?

  • And do I really need a scopemeter to read the signal, or is there a different way? (I don't have a scopemeter or the money to buy one :()


PeterH

The ignition system generates all sorts of conducted and radiated EM noise and all your electronics and wiring will need to be shielded and buffered to eliminate the noise.


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