# TACH SIGNAL CONVERTER



## mattinbend (Oct 12, 2000)

This does belong in here so I brought it back. This is the sharing of knowledge to allow us to build our hybrids, what is the problem with that?
Are you gonna lock all the posts that tell us how to change our cars illumination to blue because we are "obligated" to buy from the aftermarket?? NOPE.
So some post or mail me any info, please. I have an AEB in my vanagon and I would love to have a tach other than the VAG-COM.
If this gets locked then Vortex just got very lame. By archiving this info we allow others to benefit from our sharing of information, to lock such a thread just means you are a diaper head


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## 155VERT83 (Aug 1, 2000)

*Re: TACH SIGNAL CONVERTER (mattinbend)*

Anybody have a parts list and a wiring diagram? POST UP!!!


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## 2035cc16v (May 18, 2000)

*Re: TACH SIGNAL CONVERTER (mattinbend)*

is it so hard to run a wire from the negative terminal of your coil???








maybe I am misunderstanding...


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## Dean F (Feb 24, 2000)

*Re: TACH SIGNAL CONVERTER (mattinbend)*

If someone hear has put together their own signal conveter and wants to share that info thats one thing Matt, but buying a companies design and taking it apart and sharing what's inside with others is another, and not what the Vortex is here for.
Why not do your own R&D and post what you find here? Chances are you'd want to sell your design as well after having to put some effort into sorting it out.



[Modified by Dean F, 6:42 AM 1-23-2002]


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## mattinbend (Oct 12, 2000)

*Re: TACH SIGNAL CONVERTER (Dean F)*

Fair enough dean... Although to be realistic this is a fairly common practice in all industries... If the price was reasonable I would just buy one from Momentum but they want allota dough for an IC with a cap and three resistors
I accept the challenge and will get to work on it.
And to prove my point I will post it here for free








As far as the coil wire 2035cc16v, the 1.8T has no coil. DOH


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## 155VERT83 (Aug 1, 2000)

*Re: TACH SIGNAL CONVERTER (mattinbend)*

quote:[HR][/HR]Fair enough dean... Although to be realistic this is a fairly common practice in all industries... If the price was reasonable I would just buy one from Momentum but they want allota dough for an IC with a cap and three resistors
I accept the challenge and will get to work on it.
And to prove my point I will post it here for free








As far as the coil wire 2035cc16v, the 1.8T has no coil. DOH







[HR][/HR]​


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## 2035cc16v (May 18, 2000)

*Re: TACH SIGNAL CONVERTER (mattinbend)*

quote:[HR][/HR]1.8T has no coil[HR][/HR]​where did you say 1.8T in your post?? and yes it does, just x4










[Modified by 2035cc16v, 12:38 PM 1-23-2002]


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## vw mofo (Mar 5, 1999)

*Re: TACH SIGNAL CONVERTER (2035cc16v)*

quote:[HR][/HR]1.8T has no coil
where did you say 1.8T in your post?? and yes it does, just x4









[Modified by 2035cc16v, 12:38 PM 1-23-2002][HR][/HR]​He did say AEB.








I also don't see what so unreasonable about the momentum converter. $150... Pfft, thats nothing compared to time and money wasted trying to figure it out yourself.
Not to mention, without an osciliscope, there's no way to figure out the momentum unit. My mechanic tried. When you crack the beast open all the circuitry is completely coated with epoxy and he didn't feel like ruining a $150 piece of equipment so he put it back together. Your tach is analog like mine and the signal from your engine is digital. So at some point a DA conversion is needed and thats all we were able to figure out. 


[Modified by kkozma, 3:45 PM 1-23-2002]


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## mattinbend (Oct 12, 2000)

*Re: TACH SIGNAL CONVERTER (kkozma)*

OK I went one step further and hooked a scope up to the ECU tach signal, it is a linear curve of varying voltage, it is my guess that an IC in the instrument cluster converts this linear signal to a pulsed one that can be used to drive a Tach gauge.
I will try and post a print screen of the V vs RPM.
A quick check at my mans salvage yard revealed an A4 cluster for $50, much better than 150 for just the IC potted up in a black box.... My van will be wearing either the full cluster (if I can get the VSS to work) or just the tach installed in the stock cluster. 
kkozma: Maybe money comes easy to you . $150 is real cash where I come from, espically when a signal converting IC is $4 or so.


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## Mike0105 (Dec 31, 1999)

*Re: TACH SIGNAL CONVERTER (mattinbend)*

No offense Matt but I don't think that you asking how to copy someone else's tach signal converter is appropiate. They worked long and hard to develop the product for us the enthusiasts to use and you wanna go copying their idea. I'll leave this open cause noone has chimed in yet as to how to do it, but once they do consider it locked
Mike


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## vw mofo (Mar 5, 1999)

*Re: TACH SIGNAL CONVERTER (mattinbend)*

quote:[HR][/HR]kkozma: Maybe money comes easy to you . $150 is real cash where I come from, espically when a signal converting IC is $4 or so.







[HR][/HR]​I'm not trying to start a fight... but...
514 posts 
Bend. Or 
91, 2001, 2000 vw, vw, vw Bus, GTI, Passatt
Looks to me like you have plenty of cash...


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## vw mofo (Mar 5, 1999)

*Re: TACH SIGNAL CONVERTER (VWMike81)*

Mike:
I don't think locking the post is necessary. Even if someone does chime in and say how to convert the signal. Momentum isn't the only company out there that has one.







With the way Matt is researching this, there's no reason why he can't share. It would be a different story if he bought the momentum box and hooked the scope up to it before and after to find out what it did.


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## surefooted (May 21, 2001)

*Re: TACH SIGNAL CONVERTER (kkozma)*

quote:[HR][/HR]I don't think locking the post is necessary. Even if someone does chime in and say how to convert the signal. Momentum isn't the only company out there that has one.







With the way Matt is researching this, there's no reason why he can't share. It would be a different story if he bought the momentum box and hooked the scope up to it before and after to find out what it did.[HR][/HR]​ http://****************.com/smile/emthup.gif


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## Mike0105 (Dec 31, 1999)

*Re: TACH SIGNAL CONVERTER (surefooted)*

Well that i what I meant Keith, if he was trying to use Momentum's box to make his own I'd lock it, didn't really mean I would lock it because of his research...and foo you best not be movin in on my forum Keef








Mike


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## mattinbend (Oct 12, 2000)

*Re: TACH SIGNAL CONVERTER (VWMike81)*

OK so we can share information that we discover through effort, I assumed we could do that... Glad to have it confirmed.
And my wife paid for the Passat








To get back on topic does anyone have any knowledge or written resource showing the schematic for a 1.8T 5spd cluster??
I guess I can take apart the wifes car but I will catch a little hell for it.... I am willing to bet that the cluster has a freq to pulse converting IC that can be found, somewhere for cheap. It would be nice to go over the traces on paper before I turn screws..
And I do agree that Momentum rocks and they deserve support from the guys who checkbook their way to a dream hybrid, but none of those guys are on this forum... Right?







(xmas is over guys)


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## vw mofo (Mar 5, 1999)

*Re: TACH SIGNAL CONVERTER (mattinbend)*

You could also hack apart an A3 cluster.







Is there any information about the thing in the Bentley? About where it gets its signal from?


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## fastslc (Sep 14, 1999)

*Re: TACH SIGNAL CONVERTER (kkozma)*

Again you do not need any IC's to run a 1.8T signal on a G60 or A2 or A1 cluster. But how do you pay 2 weeks of work back ? If you go the Momentum way, $150 is sure cheap.
One trick is to find the difference how the signal comes out from a 1.8T versus an A2 or G60. From there, it's "easy"


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## mattinbend (Oct 12, 2000)

*Re: TACH SIGNAL CONVERTER (fastslc)*

Again you do not need any IC's to run a 1.8T signal on a G60 or A2 or A1 cluster. But how do you pay 2 weeks of work back ? If you go the Momentum way, $150 is sure cheap.
One trick is to find the difference how the signal comes out from a 1.8T versus an A2 or G60. From there, it's "easy" 

Ahh.... I am glad that you are so smart, this post was started to SHARE KNOWLEDGE not to gloat about secrets. Help us all out here and let us know what you know. I am trying to BUILD my hybrid, not buy my way to it.
What is it with you guys who think this is so wrong? Just share the knowledge and quit being a Hoover


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## 155VERT83 (Aug 1, 2000)

*Re: TACH SIGNAL CONVERTER (mattinbend)*

Anybody have a parts list or schematic yet...


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## mattinbend (Oct 12, 2000)

*Re: TACH SIGNAL CONVERTER (155VERT83)*

TTT
I will spend some time on this today... Just got my EGT and Boost gauges so I am a little distracted








I am going to drive my car around with an analog VOM and see what it does at increasing RPM, I also have the VAG-COM so I can get RPM to calibrate with voltage. Have to shovel the driveway out first though


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## OhioBenz (Dec 6, 2001)

*Re: TACH SIGNAL CONVERTER (mattinbend)*

there isn't a company out there that doesn't buy their competitors models and strips them down to the very bare bones & then reverse engineers them into their own product. Every automotive co does this. I worked for Hoover for 19 years and they bought every competitive vacuum model & did that. 
The key is that they do this so they can improve or use the ideas! This is with the understanding that they also then research the patents involved in order not to have patent violations.
Is the Momentum item patented? If not - it's fair game and there's no legal or other reason to lock a thread. If it is patented and he/we can work around the patent by sharing how it's done - that's also perfectly legal.
BTW if it is patented you can go online and pull the complete information as to what makes their unit different from any existing electronic technology in order to be patentable.
This IS still America right?
My 2 cents on freedom - I have no use for the item being discussed at all. http://****************.com/smile/emthup.gif


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## EuroWheels (Dec 21, 2001)

*Re: TACH SIGNAL CONVERTER (OhioBenz)*

realisticly, there is a company out there for almost anything we do, 
motor swaps are done by companies, yet we share info on swaps all day
yes, i agree this is a more technical piece of information, but i dont see what there is criticism on someones offering to make information available, 
especially seeing that according to the post above and common sence this practice of looking at products, and learning is not uncommon - post on


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## 155VERT83 (Aug 1, 2000)

*Re: TACH SIGNAL CONVERTER (EuroWheels)*

^^^


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## 155VERT83 (Aug 1, 2000)

*Re: TACH SIGNAL CONVERTER (OhioBenz)*

TTT http://****************.com/smile/emthup.gif


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## mattinbend (Oct 12, 2000)

*Re: TACH SIGNAL CONVERTER (155VERT83)*

Still going on this one. Our boy has a trumpet recital tonight so it waits... I did order an A4 cluster today and should have it by friday.
TTT in case anyone has a secrets to share


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## 1.8TsyncroB3 (Mar 7, 2001)

*Re: TACH SIGNAL CONVERTER (mattinbend)*

TTT
So, any more progress? I'm gonna need one of these gizmos as well, so I'm very interested in how it all works out.


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## 155VERT83 (Aug 1, 2000)

*Re: TACH SIGNAL CONVERTER (1.8TsyncroB3)*

TTT


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## 155VERT83 (Aug 1, 2000)

*Re: TACH SIGNAL CONVERTER (155VERT83)*

TTT


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## 155VERT83 (Aug 1, 2000)

*Re: TACH SIGNAL CONVERTER (mattinbend)*

^^^ http://****************.com/smile/emthup.gif


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## 155VERT83 (Aug 1, 2000)

*Re: TACH SIGNAL CONVERTER (mattinbend)*

^^^


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## 155VERT83 (Aug 1, 2000)

*Re: TACH SIGNAL CONVERTER (155VERT83)*


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## john stephenson (Aug 11, 2000)

*Re: TACH SIGNAL CONVERTER (mattinbend)*

Go to overboost.com and look in their online store under enginmanagment then to programable engine managment ( ? ) and they have a analog to digital converter (12v analog - 5v digital) for only $50. 
I'm not sure that this is the same thing, but at least I tried


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## Angular (Mar 12, 2002)

*Re: TACH SIGNAL CONVERTER (mattinbend)*

OK, you didn't say exactly what you are trying to achieve, but allow me to read between the lines. You have installed a late model OEM or standalone engine mangement system into an older vehicle. You have one of two problems: 1. The tach output from this new ECU doesn't tickle your tachometer's fancy or 2. you are running coil on plug or wasted spark so you have multiple coils from which there is no obvious way to obtain a tach signal.
Basically, the older tachometers that are driven off the negative terminal of the coil are expecting a high voltage spike every time a spark plug fires. The tach adapter boxes most likely have some minimal electronics but mainly what they have is a small coil (inductor) that they can use to generate a (low current) high voltage spike using the ECU's square wave tach signal as input.
I recently tore down the tachometer from a cluster out of a 2nd gen Scirocco (same as most A2 cars) and examined the tach driver circuit. There's a 2 pole RC filter circuit between the signal in and the wave shaper chip that acts as freq to voltage converter and drives the tach. I have more testing to do, but by removing one of the RC filters, I was able to get the tach to respond to a straight 12V square input.
The easiest thing for most people to do is just fork over the money and buy the damn tach adapter box. But if you're picky and don't mind doing a little extra work, you can probably find another cheaper and more creative way to make it work.


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## titeGTi (Jun 13, 2001)

*Re: TACH SIGNAL CONVERTER (Angular)*

what does the tach curve look like from a digital tach reading? is it a square wave? is it possible to:
1) hook up a signal generator to the digital tach and see what signal it takes to get different RMPs.
2) get an oscilliscope on a mk2 and earlier car and see what signal it throws to a tach.
3) compare the two signals and come up with a correlation between the two.
4) use a circuit modeler program like SPICE to come up with a circuit that would be able to realize the circuit you would need to convert one signal to the other.
i dunno if i am talking out my ass but if thats possible i have all the resources here at work to do it. i am willing to try it out if its possible since i will need a converter for my swap.


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## 16volt (Oct 26, 2000)

*Re: TACH SIGNAL CONVERTER (titeGTi)*

Its interesting, I just called MSD and they claim to not have any sort of digital to analog converter. But they make a box that sits between the 6AL and stock tach that converts the 6AL signal to work with OEM tachs. The part number is 8910. 
Im gonna run down and check it out over lunch today and see if it will work for me.


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## Angular (Mar 12, 2002)

*Re: TACH SIGNAL CONVERTER (titeGTi)*


_Quote, originally posted by *titeGTi* »_what does the tach curve look like from a digital tach reading? is it a square wave? is it possible to:
1) hook up a signal generator to the digital tach and see what signal it takes to get different RMPs.
2) get an oscilliscope on a mk2 and earlier car and see what signal it throws to a tach.
3) compare the two signals and come up with a correlation between the two.
4) use a circuit modeler program like SPICE to come up with a circuit that would be able to realize the circuit you would need to convert one signal to the other.


Any tach signal coming directly from the ECU is going to be a square wave. The only question is whether it is 12V or 5V peak to peak, and possibly the duty cycle.
The signal going to the tach on the older cars is directly from the negative side of the coil, as stated earlier. I have put this signal on the scope and can tell you what it looks like. The waveform is at or close to 0V when the coil is charging, then when the plug fires you get an extremely brief high voltage spike (100 to 300V) with some oscillation, then it levels off at roughly 12V until the coil starts charging again.
To simulate that signal, you'd need a pretty good size inductor and drive it with a transistor that can withstand the high voltage spike when the current is switched off.
I'm going to continue with my attempt to modify the existing tach circuit to work with 12V square wave input. I have a lot of other things going on right now so I'm not sure when I'll be working on it again, but I will post the results here when I have something conclusive.
If you're not afraid to tear apart the tach, you could also build your own tach driver circuit using a LM2917 freq to voltage (or current) converter. The data sheet for that IC has a sample tachometer circuit and everything.
http://www.national.com/pf/LM/LM2917.html
Bradley


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## 16volt (Oct 26, 2000)

*Re: TACH SIGNAL CONVERTER (Angular)*

So im not sure if the MSD 9810 will work. 
It has two wires, power and signal and both are pigtailed. So there really isnt any input or out put on it and it appears to have been designed to site before the 6AL and after the coil/amp.


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## Kram (Jan 11, 2002)

*Re: TACH SIGNAL CONVERTER (16volt)*

so what happened?


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## Sh0cker (Sep 21, 2003)

*Re: TACH SIGNAL CONVERTER (Kram)*


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## VRT (Dec 8, 2001)

*Re: TACH SIGNAL CONVERTER (vw mofo)*

Which Momentum is it that have the tach converter? There's like 4 out there


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## talx (Apr 4, 2003)

*Re: TACH SIGNAL CONVERTER (VRT)*

Well why do you have to get the signal off of the ECU?








Where dos it say that you need to do that?
So this is how my tacho signal converter works








4 wires spliced into the 4 wires signal ECU to coil packs then each is connected to 4 recovery rectifiers Mcc # 1n5408 that connect together and go to the RPM signal in the cluster 
It works








but im going to be using a audi TT cluster so i dont need it


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## Audi4u (Jun 29, 2002)

*Re: TACH SIGNAL CONVERTER (Sh0cker)*

Cant you just tap the negative side of any coil on the AEB motor and get the same result?


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## Audi4u (Jun 29, 2002)

*Re: TACH SIGNAL CONVERTER (Audi4u)*


_Quote, originally posted by *Audi4u* »_Cant you just tap the negative side of any coil on the AEB motor and get the same result?

Actually let me correct myself. i forgot that a coil fires 2 times for each revolotion of the engine
so you would need 2 diodes connected to coill 1 and coil 4
then connected together.
so that when the computer fires 1&4 it would send a negative pulse to the tach. the dioes are so the negative puse from coill 1 doesnt fire coil 4 and vice versa
I will try it when it gets warmer.
Andre



_Modified by Audi4u at 8:18 AM 3-11-2005_


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## illi (Mar 25, 2001)

*Re: TACH SIGNAL CONVERTER (Audi4u)*

interesting convo guys... im looking to do the opposite of what you are all trying to do... so far ive had no help in coming up with a solution...
i have a 92 GTI running a 2.0L ABA motor with distributor, and I'd like to use the mk3 cluster in my car, but have not found a way to convert the analog signal from my coil to a digital signal to the tach... since i'm going to be using a standalone engine management system rather than the OBD1 ecu/harness, i dont have a way to connect the tach in the cluster and have it work properly








i talked to someone over at dakota digital and he told me that their tachometer calibration thing MIGHT work but he wasnt 100% sure because I dont know exactly how the digital signal to the tach operates (im sure its 5v, which needs to be converted from 12v, but other than that i am lost) 
here's a link to the product i am talking about ... there's also an instruction manual link on the page...
http://www.dakotadigital.com/D...t.htm










_Modified by illi at 10:44 PM 3-15-2005_


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## 85vdub (Apr 9, 2003)

If you using an ABA just hook up the crank sensor to the cluster. It pulses once for every revolution from my understanding and should run the tach just fine.


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## illi (Mar 25, 2001)

*Re: (85vdub)*

see ive been told that the a3 cluster's tach operates off of a digital signal, rather than an analog pulse...


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## Dan R (Mar 8, 2005)

*Re: (illi)*


_Quote, originally posted by *illi* »_see ive been told that the a3 cluster's tach operates off of a digital signal, rather than an analog pulse... 

and that is correct Sir


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## Nuzzi (Oct 18, 2001)

*Re: (Dan R)*

any ideas on this: i have a obd1 coilpack vr6 in my 90 corrado g60, im still using the mechanical g60 cluster for various reasons, obviously the tach doesnt work since the g60 is off the coil and this is off the ecu, so basicly i need a D/A converter right? of course it will have to include some sort of amp circuit, so i think you said the analog tach runs off 12v right? so a D/A converter using the ecu signal in and then an analog signal out, take that analog output and amplify it as much as you need to to reach the 12v signal you would need right? you could use a number of simple op amp ICs and a couple small transformers, they dont have to be big since its small current, then a few caps as a filter circuit and you should be good right?


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## eazydaz (Apr 19, 2010)

something news?


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