clairetoo
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| posted on 15/9/08 at 08:12 PM |
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Megasquirt and rev-counter
I've tried using the search thingy and cant find anything on this allthough I'm sure I've seen a thread about such a problem - so
here goes anyway 
I picked up a bit of a bargain at Stafford - I got an 80mm VDO tacho (off the display on Europa's stand) for only £50 , so I bunged it straight
in and connected it up .
When cranking it flickers - shows about 4 to 5 hundred RPM - but as soon as it starts...........nothing 
The fact that it seems to be showing cranking RPM tell's me it is getting a signal , so why isn't it reading once the engine is running
[Edited on 15/9/08 by clairetoo]
Its cuz I is blond , innit
Claire xx
Will weld for food......
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BenTyreman
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| posted on 15/9/08 at 08:24 PM |
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How is it triggered? Do you have it running off the coil negative, or have you built the Megasquirt tacho-out circuit?
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clairetoo
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| posted on 15/9/08 at 08:30 PM |
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It is connected to a wire marked `tacho` on the megasquirt - I cant connect to the coil as I am running edis and coil pack .
I didn't build the megasquirt - and have no idea what happens inside these things - all I can say for sure is that I asked for a tacho output
when I ordered it .
Its cuz I is blond , innit
Claire xx
Will weld for food......
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Paul TigerB6
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| posted on 15/9/08 at 08:37 PM |
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Have you tried taking the tacho feed from the EDIS instead Claire?? That's what I had to do with the Tiger Supplied ETB tacho on the MegaJolt
setup that i did.
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BenTyreman
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| posted on 15/9/08 at 08:39 PM |
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The EDIS module does have a diagnostic line that can be used as a trigger if all else fails.
I used this diagram to build the circuit http://www.msextra.com/manuals/MS_Extra_Hardware_Manual_files/LowVTacho.GIF, but I can't
remember the exact resistor values. I think I used 1K and 10K to drive an ETB rev counter, which I believe uses the same electronics as VDO.
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BenTyreman
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| posted on 15/9/08 at 08:43 PM |
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The other thing is to make sure the MS is set up correctly. You have a choice of output pins when you assemble the tacho out circuit. These are the
settings that Phil Ringwood uses: http://www.extraefi.co.uk/Drawings/tacho_Wiring.GIF, but it could be one of a number of pins.
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clairetoo
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| posted on 15/9/08 at 08:45 PM |
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Can any one tell me which wire it is that can be used for a tacho on an edis - its an edis 6 by the way ?
If I need an extra circuit then I have a major problem - I can do electric's - but I know nothing at all about electronic's
Its cuz I is blond , innit
Claire xx
Will weld for food......
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BenTyreman
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| posted on 15/9/08 at 08:54 PM |
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http://forums.hybridz.org/showthread.php?t=122394 indicates pin 2. If the circuit is built, then it might be as simple as selecting the
right pin in Megatune. Doesn't it say anywhere on the case about JS3 or something similar?
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Paul TigerB6
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| posted on 15/9/08 at 08:59 PM |
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Looking at the wiring for the EDIS 6, it can only be pin 2 or 4 anyway!! I know its pin 11 on the EDIS 4 which is no use to you as that powers a coil
for you!!
With the EDIS 4 i simply connected from the EDIS to the tacho with no trouble - worked perfectly and no electronics!!
[Edited on 15/9/08 by Paul TigerB6]
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paulf
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| posted on 15/9/08 at 08:59 PM |
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You need to connect to the PIP signal, it is pin 1 on the Edis.I found it to work well with an older Smiths tacho that wouldnt work from the standard
tacho output.
Paul.
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clairetoo
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| posted on 15/9/08 at 09:08 PM |
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quote:
Originally posted by BenTyreman
http://forums.hybridz.org/showthread.php?t=122394 indicates pin 2. If the circuit is built, then it might be as simple as selecting the
right pin in Megatune. Doesn't it say anywhere on the case about JS3 or something similar?
It does say (I think , from memory...) `tacho pin 24` on the box - I will have a look tomorrow (the car is on the drive and it's a bit dark now
! )
Its cuz I is blond , innit
Claire xx
Will weld for food......
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clairetoo
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| posted on 15/9/08 at 09:11 PM |
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quote:
Originally posted by paulf
You need to connect to the PIP signal, it is pin 1 on the Edis.I found it to work well with an older Smiths tacho that wouldnt work from the standard
tacho output.
Paul.
I'm fairly sure I read some where on the main megasquirt site that that wont work with the edis 6 as it wont give the right number of pulses ?
Its cuz I is blond , innit
Claire xx
Will weld for food......
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paulf
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| posted on 15/9/08 at 09:16 PM |
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You need to select it using megatune if it has not already been set up, it is under more settings tacho output pin.You need to know which it is set to
or just try each in turn, however if it has not been set up you also need a driver transistor adding to drive the Tacho from the output.
Paul.
quote:
Originally posted by clairetoo
quote:
Originally posted by BenTyreman
http://forums.hybridz.org/showthread.php?t=122394 indicates pin 2. If the circuit is built, then it might be as simple as selecting the
right pin in Megatune. Doesn't it say anywhere on the case about JS3 or something similar?
It does say (I think , from memory...) `tacho pin 24` on the box - I will have a look tomorrow (the car is on the drive and it's a bit dark now
! )
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paulf
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| posted on 15/9/08 at 09:22 PM |
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It will if you have a 6 cylinder tacho, have a look on the megajolt site it is an option listed there for 4 6 or 8 cylinders.just push a bit of bare
wire into the back of the plug to try it, if it works which it should then make a soldered and heat shrinked connection to the PIP wire.
If you dont have the transistor driver circuit then the megasquirt output wont work.
Paul
Paul.
quote:
Originally posted by clairetoo
quote:
Originally posted by paulf
You need to connect to the PIP signal, it is pin 1 on the Edis.I found it to work well with an older Smiths tacho that wouldnt work from the standard
tacho output.
Paul.
I'm fairly sure I read some where on the main megasquirt site that that wont work with the edis 6 as it wont give the right number of pulses ?
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BenTyreman
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| posted on 15/9/08 at 09:27 PM |
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Pin 24 corresponds to tacho IN, not tacho OUT. http://www.extraefi.co.uk/Drawings/WiringLoom_VR_Hall.JPG
The tacho out is likely to be on one of the wires marked SPR, but this is mostly irrelevant. You need to know, or work out by guess-work, the internal
wiring.
The tacho signal while cranking I believe is spurious. I don't think the MS starts transmitting the tacho out signal until the engine has
finished cranking.
[Edited on 15/9/08 by BenTyreman]
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clairetoo
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| posted on 16/9/08 at 04:19 PM |
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Well.............I've now tried connecting the tacho to both the tach/diagnostic and the pip wire and......it reads..........just .
It shows about 250 rpm at tickover , and revving it will get it up to allmost 1000
The odd flickering while cranking happens even with the signal wire disconected .
It has me beaten now
Its cuz I is blond , innit
Claire xx
Will weld for food......
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BenTyreman
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| posted on 16/9/08 at 05:54 PM |
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Read this: http://www.etbinstruments.com/ETB_Gauge_Wiring_PDF/100mm_ETB_Tacho_wire.pdf
It states that when the gauge leaves the factory it is set up for 8 cylinder engines. You need to alter the dip switches to suit a 6 cylinder engine.
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clairetoo
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| posted on 16/9/08 at 06:03 PM |
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Done that before I fitted it - I downloaded the wiring instructions off the `net so they should be right .
Its cuz I is blond , innit
Claire xx
Will weld for food......
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BenTyreman
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| posted on 16/9/08 at 06:11 PM |
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Guess it's buggered then...
You could build a 555 oscillator circuit to test the tacho. Dead easy and cheap to build on a prototype board. Tune it for 50 Hz (I think) to make the
tacho read 1000 rpm.
If you have Megatune open while running the engine, does the rev counter read some multiple of the true RPM?
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clairetoo
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| posted on 16/9/08 at 07:46 PM |
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quote:
Originally posted by BenTyreman
You could build a 555 oscillator circuit to test the tacho. Dead easy and cheap to build on a prototype board. Tune it for 50 Hz (I think) to make the
tacho read 1000 rpm.
Maybe you could - but not me I could just pop out to the shed and knock out a billet alloy flywheel - but build a circuit ?
If there is any one out there who could sort this out before I destroy my engine I would be eternally gratefull..............
Its cuz I is blond , innit
Claire xx
Will weld for food......
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Paul TigerB6
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| posted on 16/9/08 at 11:54 PM |
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quote:
Originally posted by clairetoo
I could just pop out to the shed and knock out a billet alloy flywheel - but
Claire, i'm sure this must have been asked before but are you married??? Do you want to be??? 
[Edited on 16/9/08 by Paul TigerB6]
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clairetoo
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| posted on 17/9/08 at 06:07 AM |
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No time for marriage...............I'm devoting my life to making a megasquirt work
Its cuz I is blond , innit
Claire xx
Will weld for food......
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MikeRJ
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| posted on 17/9/08 at 02:09 PM |
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Claire, some tachometers don't work well with low voltage ECU signals if they are designed to work from a coil.
Have you tried connecting the tacho trigger to one of the coil negative terminals? As you are using a wasted spark the tacho will read 1/3 of what it
should, but if this works you can use a very simple circuit (a handful of diodes basicaly) to combine the coil pulses.
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clairetoo
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| posted on 19/9/08 at 05:08 PM |
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I'll try connecting it to a coil wire tomorrow - if it works , can any one build me this `simple circuit` if I need one ?
Its cuz I is blond , innit
Claire xx
Will weld for food......
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MikeRJ
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| posted on 19/9/08 at 05:25 PM |
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quote:
Originally posted by clairetoo
I'll try connecting it to a coil wire tomorrow - if it works , can any one build me this `simple circuit` if I need one ?
I'll have a dig in my spares box and see if I have a suitable zener diode, I'm sure I have the 1N4004's.
However it's a very simple circuit, have a look at the bottom of this page. That circuit is
for a four cylinder EDIS, you would simply require an extra 1N4004 diode. Some people have found they need a pull down resistor on the output as
well.
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