I purchased one these


12000RPM LCD Digital Odometer Speedometer Tachometer F1 2 4 Cylinders Motorcycle

And very nice it looks as well but connecting the tachometer pickup as follows:

Connect to the CDI output... Zilch
Connect to the coil packs .... Zilch
Connect to the injectors ..... Zilch

Wrap the feed wire around an HT lead a dozen times, it shows the idle speed but Rev the engine and it creeps up to around 2000rpm but does not go above this, I have tried less turns, around 4 and it does not sense anything.

Connect to the inductive pickup for the CDI unit and it shows 6000rmp at idle and responds immediately if you Rev the engine.

I have tried adding a 10k resistor in line and included a Zener diode when looking at the usual sources .... Zilch everything is the same as above.

Emailing China has not helped, however I did get them to send me a second one on the basis that mine is faulty but they both behave in the same way so I now have a pair.

Anyone got any ideas on how to get these to work?

There is a menu, only allows you to switch between 2 & 4 cylinders, set tyre diameter and fuel sensor sensitivity.

I bought a big tablet from China and its now a shiny table top....

This made me chuckle

Note:
The pointer offset does not affect the measurement accuracy, you can put the pointer to the in place. Please buy cautiously.

I do not know what that bit means, I was expecting it to have a manual red line pointer but it is just a sealed unit so nothing to twiddle externally as such.

I,m sure if I can get the right feed to it then away it will go, dumped the bike clocks as I wanted the adjustable speedo...



It looks like I have swapped a working tachometer for a working speedo.

With wire wrapped around an HT lead has anyone got any ideas of the voltage that is being pushed into the tachometer, is it just that 12v on the CDI unit is not enough?

Although I expect the voltage on the inductive pickup must be pretty low...

[Edited on 10/5/16 by mark chandler]

What is the coil arangmement is it wasted spark ie. one double ended coil supplies two cylinders? If so try wrapping the wire round athe plug lead on the opposite side of the coil.
With wasted spark one lead gets a positive spark the other a negative.

That's interesting, I did not know that just assumed that both coils would cause a spark positive to negative.

It's wasted spark so I will try the in a minute

Also how many turns, is there an optimum number?

[Edited on 10/5/16 by mark chandler]

this advert for one
http://www.banggood.com/12000-RMP-LCD-Digital-Speedometer-Odometer-Motorcycle-1-4-Cylinders-p-972677.html

has quite a lot of info.
especially looking at the questions/answers

It looks like someone else has the same problem then with RPM and it will not work off the coil pack wires, I think the CDI until switches to earth which could be the problem on the coil packs which is the same as the injectors.

My rev counter used to come off the wasted spark. You connect it to both signals with a diode between to stop them shorting out.

Mine comes from ecu now but it worked ok from coils


[Edited on 10/5/16 by Ben_Copeland]

I,ve done the Zener diode, albeit off just one coil pack... Nada

I have now wrapped the wire around the second coil pack lead, flat line on this one as well ...

It's clear that a nice 12v signal (which should be perfect for most tachometers is not going to work on these ones, very annoying.

weird that it can work off the CDI input, I will tap into the alternator yellow wires tomorrow and see if that gets me an approximation of RPM.

[Edited on 10/5/16 by mark chandler]

Normally on all 2 wire coils the tacho is triggered on the negative side of the coil, the positive side should be near constant battery voltage no signal for the tacho to work off.

[Edited on 10/5/16 by britishtrident]

I have tried both sides, still no good

Try a 1 M.ohm resistor. I had the same issue with my Koso, and no amount of changing the source or use of a dropdown resistor worked. Adding a 1 M.ohm resistor has stabilised it, so no more bouncing tachometer (connected on the signal wire from the coil on plug).

1M.

I have wondered about dropping the voltage down incase this is the problem, it's not a jumping tachometer, nothing at all on the main sources.

quote:

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Originally posted by twybrow
Try a 1 M.ohm resistor. I had the same issue with my Koso, and no amount of changing the source or use of a dropdown resistor worked. Adding a 1 M.ohm resistor has stabilised it, so no more bouncing tachometer (connected on the signal wire from the coil on plug).

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quote:

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Originally posted by gremlin1234

quote:

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Originally posted by twybrow
Try a 1 M.ohm resistor. I had the same issue with my Koso, and no amount of changing the source or use of a dropdown resistor worked. Adding a 1 M.ohm resistor has stabilised it, so no more bouncing tachometer (connected on the signal wire from the coil on plug).

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would that be a 1M pull up resistor?

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quote:

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No, inline with the signal. I backed it up with a 10k.ohm pull down, but the inline made all the difference.

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So you took tachometer lead to earth via a 10k resistor and collected the signal from the coil pack with a 1m resistor?

So have effectively dropped the input from 13.4v down to 0.134v

quote:

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So have effectively dropped the input from 13.4v down to 0.134v

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You really need to know what signal the tacho is designed for, 5v or 12 v pulses, pull up or pull down etc. Once you know that making it work would be relatively simple otherwise it's stabs in the dark.

Ian

Unfortunately there is very little info on these, you only know how to wire it by googling as they come with zero instructions

Lots of sellers on eBay, some include the wiring instructions with the advert, it's a real shame as they do look ideal.

Had a quick look, and the key part of interest is;-

Engine rotate speed comes from the ignition signal. The sensor wire is normally contacted with the positive side of the magnetor or directly wired on the rectifier.

I suspect you'll need a +/- signal and you'll need to do a bit of jiggery pokery with a resistor/capacitor to get your rpm pulse to swing both + and -.

Ian

Thanks Ian, that does confirm why it works off the CDI input.

Have you any idea what I need to make the CDI square wave output pulsed DC into an A/C signal.

Googling is not helping me to get from pulsed DC to AC with something very simply, my grasp of electronics is limited

[Edited on 13/5/16 by mark chandler]

Assuming there is some input resistance to gnd on the tacho input, connect a cap in series in the wire from the tacho to where ever you know you have a nice rpm signal. Without knowing the input resistance of the tacho i'd try 0.1uF, 1uF and 10uF (if using electrolytics, neg leg to the tacho).

That should do it, if not you might also need to add a resistor between the gnd and tacho input (a cap/resistor combo that normally works is 10uf and 1k5 resistor).

Ian

Thanks Ian, I will try a later on and report back.

Looking into the tachometer I record zero resistance, it must be looking for a crossover so pulsed DC will never work.

i have a 25uf capacitor lying around, so using a 1k resistor I get a decent deflection off the coils 12v, it does not work off the CDI output.

Local maplins do not have smaller capacitors in stock unfortunately so stumped for today unless I can find something smaller lying around in some scrap PCB's.

Maplins normally have lucky bags....i'm sure i've seen them in my local branch, about 20 assorted caps for a few quid. To large a cap won't discharge on the positive pulse so won't produce the negative pulse required.

Ian

I found a couple of capacitors to experiment with, using the CDI output gives better results than the coil.

0.15uF
0.47uF

tried various resistances from 1k to 10k on these, they all show the correct idle but as the revs rise over around 2000rpm it becomes unstable and over estimates.

Getting closer, Maplins local to me do not have the lucky bag in stock, they do have a 10uf however

[Edited on 13/5/16 by mark chandler]

I'm very tempted to pick one up, did some reading and people are saying it wants a pulsed -12v signal, and others say you can wire it into the "Signal generator" which I think is the crank position sensor

Double post but should help you Mark.

This guy has figured out the correct capacitor and resistor for his application - Post 29 on page 3. Not specifically your speedo but I believe they have the same internals

http://cbrforum.com/forum/cbr-600f-15/chinese-ss182-digital-speedo-installation-tips-152756/page3/

Yes they're in the ball park with 0.01uf and 100k......or 0.1uf/10k or 1uf/1k. Pick a cap and use a variable resistor to find the best value.

Ian

Some of the Koso install instructions also suggest wrapping the tach wire around a HT lead 20 times

Wrapping around the HT lead has not worked for me, I have a few bits to try tomorrow once I get back from maplins, thanks all.

quote:

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Originally posted by dave_424
I'm very tempted to pick one up, did some reading and people are saying it wants a pulsed -12v signal, and others say you can wire it into the "Signal generator" which I think is the crank position sensor

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Just an idea, but if the tacho is expecting a normally low ground signal with 12V high pulses, when you've connected it to the coil ground or injector ground, you will have only shown it a normally high 12V with short low ground pulses that it might reject.

Have you thought about trying an inverted signal from the coil ground? Just needs an NPN transistor plus base resistor and current limiting pull-up resistor to 12V like this:
link but with a higher base resistor like 100K

[Edited on 14/5/16 by R7 WSC]

Maplins let me down on parts so this is now shelved for a couple of days.

The tachometer wants to see a cross over on zero volts by the look of things, anything with pulsed DC fails to move the needle, when you look into the tachometer wire it has zero resistance.

If you'd been local i'd have popped round with some components/test gear, but google says Tadley isn't close! lol

Ian

Picked some bits up today, Ian you seem to be close to the money 10uf & 1k5 works reasonably well although reading high in the mid range, unfortunately cold starting and fireblade engines are not a good mix so it's becoming increasingly hard to start the engine now.

I tried increasing the resistor to 2k4 which has not helped, I will try going the other way tomorrow by wiring them in parallel and see if this helps.

I also tried a 0.01uF capacitor with 100k resistor, this reads higher in the mid range than the 10uf solution, if I,m honest neither solution is that far away from my experiments with the 0.47uf or 0.15uf capacitors.

It's a bit of a pest! Good thing I never watch the thing anyway when sprinting.

I've just ordered one of these UK Motorcycle Bike LCD Digital Odometer Speedometer Tacho Gauge Background Light

Should be here in a couple of days so I'll see if I encounter any similar problems. I believe the internals are probably very similar. If I need to filter the RPM signal I will use Ian's suggestion of a fixed capacitor value and a variable resistor

quote:

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Originally posted by mark chandler
Picked some bits up today, Ian you seem to be close to the money 10uf & 1k5 works reasonably well although reading high in the mid range, unfortunately cold starting and fireblade engines are not a good mix so it's becoming increasingly hard to start the engine now.

I tried increasing the resistor to 2k4 which has not helped, I will try going the other way tomorrow by wiring them in parallel and see if this helps.

I also tried a 0.01uF capacitor with 100k resistor, this reads higher in the mid range than the 10uf solution, if I,m honest neither solution is that far away from my experiments with the 0.47uf or 0.15uf capacitors.

It's a bit of a pest! Good thing I never watch the thing anyway when sprinting.

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I purchased it for the odometer, if it's fat in the middle it does not matter that much to me, sitting for a static noise test I expect it will even help.

I have two of these now, both have the same deflection.