SuzukiSavage.com - Building a DIY tachometer

RocketScienceSmurf

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Building a DIY tachometer
04/05/19 at 04:54:23

I thoiught it would be fun and educational to build my own arduino-based tachometer so a few weeks ago I hooked up my oscilloscope (Hantek 1008) to the bike and let it idle for a couple of seconds. The signal looked VERY good and I though "hey, this is a usable signal".

A couple of days ago I had made what I believed to a working code which I uploaded to my arduino but it did not work as expected. I got very weird numbers so I hooked up my oscilloscope again and this time things did not look as "clean" as before so at first I was afraid I had broke something, but the I realized my time base was different. The bandwidth of the 1008 is quite low so when I "zoomed" in on the ignition pulse the first time the resolution was very low and as a result the signal looked way smoother than it actually was. Now I have a better view of the ignition pulse so my question is: How do people clean up/filter the pulse? My guess would be some kind of LC-filter, but care must be taken so it wont mess up reading at higher rpms.

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RocketScienceSmurf Senior Member Offline SuzukiSavage.com Rocks! Posts: 268 Sweden Gender:	Re: Building a DIY tachometer Reply #1 - 04/05/19 at 04:55:47 Oscilloscope view with proper 20ms time base. The first image looks like a 20ms also, but the actual time base was 500ms
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RocketScienceSmurf Senior Member Offline SuzukiSavage.com Rocks! Posts: 268 Sweden Gender:	Re: Building a DIY tachometer Reply #2 - 04/05/19 at 04:56:14 Closer look at the ignition pule
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mmccarty YaBB Newbies Offline SuzukiSavage.com Rocks! Posts: 4	Re: Building a DIY tachometer Reply #3 - 04/10/19 at 23:50:33 An RC filter as a low pass filter, A resistor in series with the signal and a capacitor to ground. The values of the combination will set the cutoff frequency...
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RocketScienceSmurf Senior Member Offline SuzukiSavage.com Rocks! Posts: 268 Sweden Gender:	Re: Building a DIY tachometer Reply #4 - 08/04/19 at 05:13:00 I think I have found the reason my old optocoupler died on me and why the "ceiling" of the signal looks so flat. There is a spike sometimes reaching over 400V when the ignition coil fires.
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RocketScienceSmurf

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Re: Building a DIY tachometer
Reply #5 - 08/04/19 at 05:17:53

I installed the only choke I had lying around, a Hammond 159ZB with an inductance value of 320mH and I put a 680 Ohm resistor to ground after the choke as a load.

Now the signal looks MUCH better. This choke is a bit too big but I think I have found an axial one of 100mH that will probably work.

I know a RC filter will probably work as well but I wanted to explore what a series inductor did to the signal. It has cleaned the signal up very well and completely eliminated the negative ringing on the signal.

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Matchless G11

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Re: Building a DIY tachometer
Reply #6 - 08/04/19 at 05:36:46

I would be careful of that big of a choke, It might kick back into your Arduino and fry it. something like 2.5 mH might work better. (and even with that one might put a diode across it (like done in driving a relay) to protect it

Might I suggest running your signal into a buffer/ Schmitt trigger.
and on the input of the buffer use some Zener / tvs diodes to protect the buffer form the high voltage spikes.

What you don't want to do is kick back into you ignition module. I see you are trying to load it properly with the resistor. good luck.

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RocketScienceSmurf

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Re: Building a DIY tachometer
Reply #7 - 08/04/19 at 06:16:23

Great idea with the zeners. I actually just discussed that with a friend of mine. I think a ~15v zener after the choke will give a smoother signal to work with and probably remove the 30-40V peak. However the current choke has a DC resistance of only 7 Ohm so I think I will wait until I get the new choke that has a DC resistance of 75 Ohm. That will probably put less strain on the zener.

My plan is to connect the inductor to an optocoupler through a small constant current LED driver (and a resistor to take some load of the constant current driver).

Is there any risk of kick back to the CDI with my current setup? The arduino is not connected yet. I am trying to find a good way to clean the signal going to the ignition coil first.

This inductor I can get fairly easy. The only other value my supplier stock is 330uH which is probably not enough, but I can get both and see how they compare and perform.
https://www.mouser.com/ProductDetail/Vishay-Dale/IHD3EB104L?qs=qjrtsYR%2FpVXE...

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Matchless G11

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Re: Building a DIY tachometer
Reply #8 - 08/04/19 at 07:39:35

Hi kamelryttarn.
I don't know your entire set up, nor am I knowledgeable with Suzuki's ignition box set up so I will be hesitant to say ya or nay on what is safe to hook to it.
having said that

1 be carful of reactive loads, high impedance resistive loading may be the best. You can always run some sort filter after a unity gain buffer amp.

2. Be leary of your voltage levels, and ground loops that might form.
the bike is twelve volts and the Arduino (does have a reg and I have run mine off of 9 volts,) but the board is 5 volts.

I would look at what other people are doing putting a tach on these bikes
just to be safe.

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batman Serious Thumper Offline SuzukiSavage.com Rocks! Posts: 3806 osceola new york Gender:	Re: Building a DIY tachometer Reply #9 - 08/04/19 at 10:38:48 There is absolutely NO chance of kick back hurting the CDI ,with your present set up or any other, but ONLY because the bike doesn't have one. It has a TDI. While I have no knowledge of electronics I do find your project interesting.
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justin_o_guy2 Serious Thumper Offline What happened? Posts: 55279 East Texas, 1/2 dallas/la.	Re: Building a DIY tachometer Reply #10 - 08/04/19 at 10:52:55 It's over my head, but I certainly applaud the effort.
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batman Serious Thumper Offline SuzukiSavage.com Rocks! Posts: 3806 osceola new york Gender:	Re: Building a DIY tachometer Reply #11 - 08/04/19 at 12:44:52 JOG ,I think it would be something if they came up with a Tach we could build ourselves . I was lost too, the only thing that registered with me was when they mentioned, kick back.
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justin_o_guy2 Serious Thumper Offline What happened? Posts: 55279 East Texas, 1/2 dallas/la.	Re: Building a DIY tachometer Reply #12 - 08/04/19 at 18:04:32 I have a few more hours than required for an associates degree in electronics from the air force. I repaired copiers and cash registers for seven years. I'm still blown away by the knowledge these people are exhibiting.
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