eBay Motorcycle Tachometer wiring

junglepig

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Oct 30, 2018
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218
I have this same tach. It arrived today. It's a really nice looking unit. But I will need to build a driver circuit to give the sort of signal it needs.
I haven't found specs for it yet, so if anyone knows what it is looking for, I can make a circuit that works.
I will have 12V system available. I'm guessing it just needs a 12V pulse like one could get off the primary coil of an automotive system, right?
So if I set up a circuit that switches 12V to it every time the blue wire goes above a positive threshold, that would probably work, no?

EDIT: So I watched the video above, and they throw up a schematic at the end of it that is what I was envisioning:
1543981887703.png

Most any NPN small signal transistor should work.
I'm planning on adding a lower voltage coil to my magneto to derive my 5V and 12V systems, so I'll probably drive the tach from that coil rather than the blue CDI wire.
If anyone has built similar for their CG yet, let me know.
A 12V source is necessary in general for this tach, so I'd love to see other people's solutions too.

EDIT #2:
Since I ultimately plan to have an arduino or raspi on board to collect engine data, if I use a version of this circuit to drive the tach, I'd also add a 5V switching output as well for the input to the micro. I'll share when I get it going.
A bigger challenge for me is to make an attractive mount for the tach. I have a 10mm mirror mount clamp that will probably work...
 
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Phabbits

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Aug 7, 2017
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19
Hey junglepig,

I recently got access to an oscilloscope, and so should be able to give some info of the signal for when the tach does read, around 6000rpms according to the un-adjusted tach. Unfortunately my bike is currently broken down, but after I get it running again I will post back the results and hopefully they can help us both to create the correct circuit.
 

junglepig

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Joined
Oct 30, 2018
Messages
218
Hey junglepig,

I recently got access to an oscilloscope, and so should be able to give some info of the signal for when the tach does read, around 6000rpms according to the un-adjusted tach. Unfortunately my bike is currently broken down, but after I get it running again I will post back the results and hopefully they can help us both to create the correct circuit.
Sounds good. I have a scope too. I don't have all my parts yet, but I'm planning on winding my own auxillary lighting power coil on the mag, since they don't come with that feature anymore. It will charge up a USB power bank. My headlight will be a 5V LED unit, but my tail and turn signals, horn, tach, etc is all 12V. If my 12V needs are small enough, I'll just boost the 5V from the USB pack. But I think I'll be happier with a 12V system separate from my USB pack. Either a small ultracap bank, or separate lithium pack near enough to 12V.

I'm happy to collaborate and share.
 

JerboaJohn

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Joined
Jul 29, 2018
Messages
677
I thought I saw something like a universal Hall sensor tach you can wire up easy, just need to mount a tiny magnet on a flywheel or output shaft semi-hard part), then mount the threaded sensor (easy part)
trying to remem what I was looking at that time or where I saw it, it was last month.
those bicycle computers that have a magnet on the spokes are the same idea, except this tach needs 12v ran to it
 

Phabbits

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Aug 7, 2017
Messages
19
It has been quite a while! Just an update...

Things finally worked out where I could test the bike with the oscilloscope for the first time; on break halfway through my linear circuits class, got the bike able to run for a little bit, and some nice weather!

The oscilloscope I am using is a DSO3062A, and I could not get the driver for my new laptop, so I had to take a picture of my initial findings.
86378

Not too helpful, and I did not have time to adjust it because my bike had vibrated quite a few things loose, and was running rough.

I did however get the oscilloscope to connect to an older Windows XP laptop now, so if I have time before I head back from break, I will try and get better data.
 

Tom from Rubicon

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Feb 9, 2016
Messages
318
Phabbits
The first photo of your bike I said out loud to myself " The dude is an Electrical Engineer". A bike almost obscured by conductors. Like a rolling bread board. I'll follow to see how you sort this tach install out.
Tom from Rubicon
 

Phabbits

New Member
Joined
Aug 7, 2017
Messages
19
I have that tach/speedo and works great. I have all the functions working, tach,speedo,signals,hi/lo beam. Just no fuel level.
Hey mybike!

Great to hear someone got the tach running on a motorized bike! Also very impressive setup you have there!

Was there anything special that you had to do to get the tach working? Or was it just a "Plug 'n Play" in your case? Also what kind of motor are you using, looks very nice!

Thanks for chiming in,

Phabbits
 
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