Edis with stock tacho

[Anders]

Please someone tell me how you got your tacho to work with edis ignition i have installed the diods as suggested in the megasquirt manual but the tacho keep jumping like crazy.

[markandson]

I will be getting there soon, my tach is not operating at all with the EDIS4 and the MegaSquirt. When I figure it out I will post my answer, may take me a few days.

[wrench459]

Looks like you'll need a zener also.

[Anders]

I am using two diods and a zener diod as the manual disqribes

[wrench459]

I'm going to assume that the engine is running good.
The only problem is a misbehaving tach?
I would love to have a waveform pattern of the tach input.

[Anders]

the engine is running fine i just cant get the tacho to work properly.

[Dennis Texas]

Originally Posted by Anders Please someone tell me how you got your tacho to work with edis ignition i have installed the diods as suggested in the megasquirt manual but the tacho keep jumping like crazy.

I had similar problem with another type electronic module replacement for points, tach would be erratic, ending up having to add resistance to the coil the extra load cleared the problem up.

[garrymc]

Hi.
Did you try pin 2 on the EDIS?

Cut and paste from the meagmanual...

You may be able to use the IDM (Ignition Diagnostic Monitor) output to drive the tach. IDM a signals that the primary side of the ignition coil has fired. Simply wire the IDM output (pin 2 on all the EDIS modules) to the tach input

Garry

[Anders]

Yes both 2 and 11 pin on the edis modul with zero result pin 2 works fine on my friends kitcar but it is a different kind of tacho. I found the exact way on a homepage where someone with a old BMW described how to get a old tacho to work but the link is no longer working.

[Dennis Texas]

Originally Posted by Anders Yes both 2 and 11 pin on the edis modul with zero result pin 2 works fine on my friends kitcar but it is a different kind of tacho. I found the exact way on a homepage where someone with a old BMW described how to get a old tacho to work but the link is no longer working.

The tachometer in these older cars have to see what would be expected if you had a coil and points in the car. It needs a definite pulse discreet and fairly clean. if you have a bad condenser or too close a gap even on original points you would see the same effect on the tachometer. I'm not familiar with your exact setup but I can almost guarantee that if you get a good crisp on off signal the tach will work. Look at what ever signal the electronics are looking at and get a load box and see what is needed to enable tach to see the switching. I'm not understanding the zener diode purpose (is it's rating 12V) since it is a limiting device but packs a bit more wallop in the specified range of where it rated in volts I believe it works off the reverse curve little change creates large offset in amperage. Triumph motorcycles used that exact principle in their charging system on the 650 CC for sure.
Anyway back to the tach if you cannot find a solution take it to a shop that has a method to look at the output of the electronics your using for the tach and look at signal if it is not discreet you are going to need to add some load to make the system respond as a coils and points would.
I can remember a specific problem with magnetic speed controls we had incorporated some newer processor electronic controls, the system did not work we had to actually add a relay ( it created a load) to the out signal and use the contacts to give the signal to the old pre existing equipment. there is always a way around technology I believe if you get a scope and actually looked at signal you would not see a crisp return to zero, I think you would see random voltage levels before new high is hit. It appears to tach the the level maintained is zero and the increase is based above that reference that why tach floats around and bounces. JM2CW

[garrymc]

Originally Posted by Anders Yes both 2 and 11 pin on the edis modul with zero result pin 2 works fine on my friends kitcar but it is a different kind of tacho. I found the exact way on a homepage where someone with a old BMW described how to get a old tacho to work but the link is no longer working.

What was the address of that homepage for the old BMW???

I thought I had saved some info on something simular, but can't find it now.

Do this pictures look familiar.

I'm sure there is someone at the megasquit forums who will know what we need.

[Anders]

That is probably from the link a saved but now is gone. i remember those pictures

[garrymc]

I remember it too now. It crossed my mind what they did to the BMW could transfer to the Opels. I recall it being a VDO gauge. If you still have the url of the web site we would could try the way back machine.

[markandson]

Originally Posted by garrymc Hi. Did you try pin 2 on the EDIS? Cut and paste from the meagmanual... You may be able to use the IDM (Ignition Diagnostic Monitor) output to drive the tach. IDM a signals that the primary side of the ignition coil has fired. Simply wire the IDM output (pin 2 on all the EDIS modules) to the tach input Garry

I also have pin 2 connected from my EDIS module and the tach does absolutely nothing, I have not tried to fix the problem yet, I am still working on getting my engine to idle.

[Dennis Texas]

I don't have one of these units so I can't be positive but just from looking at that drawing that circuit is using 22 volt rectified signal (diodes passing a positive pulse from the coils) firing a zener diode and dropping the supplied voltage from the coil across the pull up resistor 100 K.
Zeners work in the negative curve (reversed biased thats why it is drawn in circuit what appears to be backwards) they deliver at their rated voltage.


one area you might look at if your coils are actually 12 volt not 22 volts

the pull up resister is 100K and that
1N4748ADICT zener is rated for 22 volts @ 11.5 ma seems to me to be the wrong zener diode t (unkess the coils are actually being fired with a 22 vdc signal). I don't think that circuit is turning on the zener .

1N4742ADICT zener is rated for 12 volts @ 21 ma

when the circuit is working correctly, the voltage path is through the pull up resistor, it developes the voltage dropping the postive signal from the coil across the resistor, the tach sees what ever that voltage is across the resistor electrically


I don't think the zener is working correctly in that circuit if the coils are 12 vdc. Once the circuit is firing and turning the zener on, the only thing left to play with is resistor size to develope the right load (voltage) for the tach to respond to.

http://dkc3.digikey.com/PDF/T081/1261-1267.pdf look at the values

Just some fuel for thought while sitting at work looking at that diagram.

[markandson]

Anders, don't know if you have seen this part of the msefi site but it is how I learned how to configure the EDIS unit and connect it to MegaSquirt. The very bottom of the document has info on how to connect a tach to the EDIS module if you are having problems. The connection diagram is exactly as you have previously tried but the part numbers are different, here is the link to the EDIS page.

[markandson]

Originally Posted by Dennis Texas 1N4748ADICT zener is rated for 22 volts @ 11.5 ma seems to me to be the wrong zener diode

I am a little confused, the diagram shows 1N4746ADICT, where did you get the number from that you believe is wrong? Maybe I just missed something .

[Dennis Texas]

Originally Posted by markandson I am a little confused, the diagram shows 1N4746ADICT, where did you get the number from that you believe is wrong? Maybe I just missed something .

Yes forgive me (over 55), the monitor at work is a 15 inch crt now that I am on my 24 inch digital at home I can see it is a 46 not 48 but even that model shows to be 18 volt @ 1watt. I think I just saw what that zener is for it acts like a gating transistor it does not saturate until driven 18 volts then saturates so instead of a positive going saw tooth it would be a pulse. Are your coils being fired at 18 volts?

I didn't mean to confuse I like to work on electrical problems and I was playing with that diagram this early morning at work I was putting expected signals on it and the assumed value of 22 volts didn't appear to be right, I was sure that was going to be the answer so I put it out there. I don't see a purpose for the zener unless that zener is being used to change a positive going saw tooth wave input from the rectifying diode thats triggering it to a more square pulse at the 18 volt mark. It's purpose appears to act like a gated transistor, Only suggestion I would have left without a scope signal is are your coils seeing a 18 volt pulse to be triggered?

[Anders]

I was afraid that the answer to my question would raise even more confusion than before i would like to explain that i don't know anything about electronics. my hope was that someone who are using edis ignition and got there tacho to work would explain or show there wiring diagram and what components they used. I am grateful that people take their time too try to help me but i need info that is so precise that a child would understand it.

[markandson]

Originally Posted by Anders I was afraid that the answer to my question would raise even more confusion than before i would like to explain that i don't know anything about electronics. my hope was that someone who are using edis ignition and got there tacho to work would explain or show there wiring diagram and what components they used. I am grateful that people take their time too try to help me but i need info that is so precise that a child would understand it.

I will try to get mine working and let you know.

[Dennis Texas]

Originally Posted by Anders I was afraid that the answer to my question would raise even more confusion than before i would like to explain that i don't know anything about electronics. my hope was that someone who are using edis ignition and got there tacho to work would explain or show there wiring diagram and what components they used. I am grateful that people take their time too try to help me but i need info that is so precise that a child would understand it.

Sorry I don't have one of these I could be of more help and give you a parts list and a drawing but looking at the diagram and the site I think the problem lies in the zener diode is not turning on for whatever reason. In the other set up with the diagram on the post, it looks like the internal resistor is bypassed with a piece of wire and an external resistor was used in it's place. Just be sure you put the zener diode in the circuit as it is shown even though it appears backwards.

Don't know if drawing helps or not signal 1 and 2 are being applied each 360 degree rotation of the crankshaft signal 3 is the signal of both coils see how it is 4 pulses signal 4 is where I think your problem is your not getting the output from the zener the zener is set for 18 volts it is not turning on.
My time is of no issue I'm at work trying to kill time can't speak for anyone else. Due to the nature of the beast the actual signals with coils being inductive may vary it is just for illustration. Signal point 3 and 4 is where you would look to see what the circuit is doing with a scope. Only difference should be the look of the pulse, timing will be exactly the same. Feel free for anyone to correct me.

[markandson]

Stopped at Radio Shack on the way home and picked up 1N4004 and 1NT4742 which is a 12V Zener, probably won't have time to play with them until this coming Saturday.

[wrench459]

Don't forget cranking voltage is around bear min. 9.6 volts.
A zener with a 8 volt threshold sounds better.

[markandson]

I assembled the circuit exactly as shown in the EDIS portion of the msefi.com site and my tach works perfectly. All the parts were purchased at radio shack and I had a small piece of universal circuit board laying around from my college electronic days so I soldered it all to that with 1/4" tabs sticking off of it to be able to attach push on terminals to it. The circuit board is about 1 1/4" square, I just have to waterproof it and voila! Anders I don't know why your tach will not work, maybe it is the tach itself. I did use the 12V Zener and it does work during cranking, but even if it did not I don't think I care about cranking RPM only need the tach when my baby hums .

[Anders]

Thank you so much for taking your time to help me! I know that the tacho is ok tried it with a signal from my fathers ascona and it works ok. I will get new diodes and solder them in and check if this will work.