Tacho Signal Converter

[Dixon 1]

I've bought and installed a tacho signal converter (from QEP) to convert the signal from my Gti-6 ecu to the 205 rev counter.

It's all wired up correctly, 4 wires to the unit (earth, 12v, signal from ecu and signal to 205 tacho) and I've checked that I am getting a signal from the ecu with my multimeter and that I've got a good earth and 12v but it isn't working..

 

QEP have been really helpful and are quite happy to take the unit back to test it and send out another but he's never had one fail before and said they are tested 3 times before being sent out.

He said that they defiantly work with the S16 ecus (which is the same as an aftermarket one, DTA??) and cant see why it wouldnt with the gti-6. Is this right? Will they have the same output?

 

Has anyone else used the unit with a gti-6 conversion?

 

Could there be something else wrong that Im missing or not done correctly?

 

Any ideas much appreciated as it would be nice to have a rev counter working for when I go to Cadwell Park at the weekend.

[madspikes 41 1 Cars]

I've done some playing with the standard 205 rev counter and got it working with the tacho out from the MS ecu. What signal comes out of the gti6 ecu?

[Dixon 1]

I've done some playing with the standard 205 rev counter and got it working with the tacho out from the MS ecu. What signal comes out of the gti6 ecu?

 

I get 11v out from the ecu and when I raise the revs the voltage drops with the higher revs.

[Sam 4]

They look like standard 205 dials only better looking and with numbers for temperatures etc. Also backlit in eighties green

[madspikes 41 1 Cars]

Are you measuring that with a multimeter or a scope?

 

The standard rev counter works by counting the number of high low / low high transitions, the quicker they happen the higher the rpm.

 

So I'd expect a square wave +12 to 0v out of the Ecu, this however cant be measured using a multimeter as it changes so often.

[Dixon 1]

I'm using a multimeter to measure it all.

 

The signal out from the gti-6 ecu shows a constant 11v then drops when revved.

 

So I'm expecting to see this +12 to 0v out from the converter box which I can't check with the meter. I'm trying to get hold of a scope to see what I'm getting.

 

Anyone know if the output from an S16 ecu is the same as a gti-6?

 

Assuming the box is doing what it should, is there anything else I should be checking?

The tacho was working fine with the 1.6 engine before the engine swap by the way.

[pug_ham 240 3 Cars]

Anyone know if the output from an S16 ecu is the same as a gti-6?

I think the output is the same from all ecu's that supply the rpm signal, Sams findings show they are from the omex & MP3.1.

 

Try asking jonnie205 how he's done it He has wired a couple of GTi-6 engines in & sorted the rev counter.

 

Graham.

[Alastairh 47]

Out of intrest how much do QEP sell them for?

[rich_w 0]

I'm using a multimeter to measure it all.

 

I believe multimeters arent quick enough to the measure the voltage, you need a 'scope to see it.

[sonofsam 5]

I have an oscilloscope your welcome to borrow, but I fear Im a bit to far away!

[veloce200 3]

I have an oscilloscope your welcome to borrow, but I fear Im a bit to far away!

 

i know this is very unhelpful but which wire do you connect to the 205 tacho (is it obvious if you remove the instruments?) as I need one of these for mine -2 yrs without a tacho is annoying !

[madspikes 41 1 Cars]

Interesting thread...

 

I'm running my rev counter from a +5v to 0v signal, no special boxes! If can remember rightly the rev counter works with +12 to 0v signal as well (after being modified).

 

I will document my rev counter at some stage, when I have some spare time....

 

All I did was cut the track near the first pin of the IC (chip) isolate it from everything else. Then I applied my rpm signal to that. You need to supply the rev counter with +12v and 0v but everthing spring into life with me. I also changed a resistor for a variable resistor to calibrate it.

 

Out of the ecu I expect your getting a normmally high signal, ie it only goes low for a short period of time, hense the +11v. I expect out of the box your getting a normally low signal, and hense the low reading. I expect the box only produces a very short +50v (ish) spike to simulate the coil pulses, which the multimeter doesnt pick up.

 

If your intrested i'll post some pic this evening.

 

Mad.

[sonofsam 5]

i know this is very unhelpful but which wire do you connect to the 205 tacho (is it obvious if you remove the instruments?) as I need one of these for mine -2 yrs without a tacho is annoying !

 

Wich wire from the 'scope? Dont know as its only ever been plugged into my mixing desk:D I've learnt to live without a Tacho, can hear when to change gear

[veloce200 3]

Interesting thread...

 

I'm running my rev counter from a +5v to 0v signal, no special boxes! If can remember rightly the rev counter works with +12 to 0v signal as well (after being modified).

 

I will document my rev counter at some stage, when I have some spare time....

 

All I did was cut the track near the first pin of the IC (chip) isolate it from everything else. Then I applied my rpm signal to that. You need to supply the rev counter with +12v and 0v but everthing spring into life with me. I also changed a resistor for a variable resistor to calibrate it.

 

Out of the ecu I expect your getting a normmally high signal, ie it only goes low for a short period of time, hense the +11v. I expect out of the box your getting a normally low signal, and hense the low reading. I expect the box only produces a very short +50v (ish) spike to simulate the coil pulses, which the multimeter doesnt pick up.

 

If your intrested i'll post some pic this evening.

 

Mad.

excellent work ! it's an emerald so gives out 12v. do you think this would cause it to overread/damage the IC? where did you put the pot? I suspect calibration is necessary. bought a cheapish tacho for a mates car we put emerald and when installed it was nearly 800rpm out !

sonofsam - i've been using an indicator light on the dash as a shift light but i just miss my tacho!

[jochem 0]

I've had my gti6 on the scope, the guy who helped me gave me this drawing:

 

[whizzer71 0]

Just dump the converter box,wire it up with diodes resistors etc,cant remember exactly how i did mine but it was with help from Hilgies diagram,all the components were sourced cheaply on the net from Maplins....loads cheaper than the overpriced converters.

Rev counter works spot on with the rev limiter cutting in at 7200 which i believe is when the ecu cuts the injectors so cant be that far out !

I still have a copy of the diagram but havnt a scanner to re post it with but Im sure if you mailed Hilgied he would be happy to help.

 

Good Luck

 

Tris

 

s

[petert 550]

Interesting thread...

 

 

All I did was cut the track near the first pin of the IC (chip) isolate it from everything else.

 

 

Interesting! Could you please elaborate?

[madspikes 41 1 Cars]

What are you asking? Are you asking why that link is interesting or do you want more details?

[B1ack_Mi16 67]

What are you asking? Are you asking why that link is interesting or do you want more details?

 

I guess he asks for more info regarding connecting a sine-signal from ECU directly to pin1 on the chip in the revcounter board?

 

And if that really works it will make it so much easier to get this to work.

 

Probably showing with a picture or drawing which of the pins that are nr. 1?

[madspikes 41 1 Cars]

This works using the square ware output from either a signal generator or my megasquirt tacho out.

 

 

 

Cut the tracks by the blue markers.

Red marks show the pin where the new tacho input signal should be applied.

Yellow shows where the tacho wire needs to go if your using the standard loom.

 

 

 

I removed the resistor that was mounted here and replaced it with a 50k variable resisor so I could calibrate the system.

 

To test it before connecting it to an ECU:

Connect the tacho up to +12 and 0v (red +12, blue 0v)

Then make and brake a connection to the new tacho input with either +5v or +12v. The quicker the on off, the higher the rpm.

 

If you connect the tacho up to the old coil after these mods you WILL blow it up!

 

**** I hold no responsibility to any damage caused by trying this *******

This just details what worked for me.

Edited December 5, 2006 by madspikes

[smighall 1]

Could you elaborate on how you used the variable resistor to callibrate? How do you know what rpm the engine is doing in order to calibrate it correctly?

 

Looks very interesting!

[madspikes 41 1 Cars]

This is where it may fall down with a lot of people.... I used a known signal input (from a signal generator) to make sure that the tacho was reading right. Adjusting the pot changing how the tacho reacted.

 

This may not be necessary, as my tacho had been buggered around with before I got it. It didnt read right as standard.

[B1ack_Mi16 67]

This is where it may fall down with a lot of people.... I used a known signal input (from a signal generator) to make sure that the tacho was reading right. Adjusting the pot changing how the tacho reacted.

 

This may not be necessary, as my tacho had been buggered around with before I got it. It didnt read right as standard.

 

Did you not test it with a sine wave too, I think I read that in another post?

Most ECU's got sinewaves which is what causes the trouble I think.

[madspikes 41 1 Cars]

Sine / Square / Triangle wave forms should all have the same effect, its just a thrshold crossing. I'm sure I've checked this out, but I'll give it another go when I get a chance.

 

I'd be surprised if ECUs give out sine waves, a square wave is much easier to do, as its just on / off. I'm not saying your wrong, just that I would be surprised.

 

Mad.

[cybernck 400 1 Cars]

standard 205 GTI rev-counter works off square wave form btw .