Dave you make it sound easier than it really was. That thread had its ups and downs and it takes some time to sift thru the back-and-forth that went on. Others can take a read and endure some of the difficult contributions by Loren

http://forums.pelicanparts.com/porsche-911-technical-forum/316555-964-distributor-3-2-twin-plug.html

Patton got it figured out and kudos to him. But I think Sal's knowledge here may prove to enhance what was done before. There was a lot of trial and error and I think Sal has a better grasp on how to approach this. I like the 964 coil approach because it shares the same coils as the 3.2. Whereas the 993 module approach by Patton created some different challenges due to the different coils?

Kevin,

I approach electronics from a specification based analysis, guessing is not a good idea :). First thing I did was get the specs for the 964 ignitor module and it says that the trigger line is 0vdc at 0ma of current with coil turned off. But to turn the coil on it requires the trigger to be at 5vdc and can draw 10-20ma, you can't drive 20ma with a simple TTL chip! And we have two ignitors to drive so I designed a drive circuit good for at least 100ma safely. Side note, the Andial circuit design does not meet this spec.

Then I needed to know what the DME coil drive (pin 1) spec was but this I had to test to figure out. Once I knew the output signal from the DME I created custom circuit to drive the Ignitor module per spec.

I have the prototype working. Furthermore no design I've seen so far works like mine. Andial drives directly from a 4093 Hex Driver chip but this is good for no more than 8-10ma so it never meet spec in the first place. But of course it works but working isn't necessarily the best design. The other attempted circuits I've seen all used a NPN transistor but this design isn't that good to mate to the DME coil drive line since the drive line pulls to ground. A better design is to use a hi-side PNP transistor, this is what I based my design on.

It's not complicated to figure this out for someone with the background to do this type of analysis but it's naive to think it's simple. I've already spent more than 15 hours just on the design, working through several design ideas even before anything was built.

The solution I have in mind and already working is a simple 4 wire hookup all done in the engine bay and you don't cut any factory harness.

Certainly others can figure this out but I'm trying to figure it out and possibly market the solution as a simple drop in. Ideas are easy, execution not so much :(

Here's the early prototype working in my 84 3.2L, one coil driving the dizzy the other coil driving a spark plug in ambient air. At this time I'm taking critical current measurements on the input and output signals, I calculated current numbers based on specs but I also want to actually measure what the input line draws and what the output line supplies to be sure the assumptions (calcs) were correct.

See in action here:
https://www.youtube.com/watch?v=G4EJXtj_ZtM
That's with motor running and the other coil firing the plug sitting on the table.
Near the end of the video you see the oscope, the top trace is the input signal and the bottom trace is the output that drives the Ignitor, notice how clean the output is and exactly 0-5vdc signal with very clean on and off edges. You also see how the input and output are 180 degree reverse of each other, that signal reversal is what's required to use the stock DME signal to drive the Ignitor from the 964.

Once the prototype is done it then goes onto printed circuit boards and packaged into a sealed plastic housing that's 100% weather proof.

Actually, it's quite simple to design one without using any semiconductors, i.e. PNP,
and it has been posted on a Pelican Parts Forum thread not yet linked to. It hardly
takes ten years for someone to appear with the knowledge to design a twin plug
driver circuit as originally posted on this forum using two 964 modules.

Again, the search button is your friend!

Dave,

Please share the design you have in mind without any semiconductors. And no mods to the DME or the factory harnesses. I'd love to see such design, can you please point us to that thread or documentation. I really do not understand you, why would you not post the link if you know where such a design is located! You truly are a different breed! It's a complete waist of time to even entertain you.

Do you mean this thread?
http://forums.pelicanparts.com/porsche-911-technical-forum/316555-964-distributor-3-2-twin-plug.html#post2951912

And are you saying to use the tach signal? Please elaborate if you care to be helpful.

I also can't find the thread, but if I remember correctly it used one of the two 964 modules
as the inverter for the second module driving the second coil, i.e. the inverter input signal
came from the standard 3.2 coil signal (DME pin 1) via a few resistors placed in the harness
for the modules. This required no changes to the DME computer nor its connector.

Dave,

That's a reasonable thought idea to use one ignitor stage stage to do the invert of the signal, so you could solve the inversion part via a clever method such as this. But we still have the problem that the ignitor input (trigger line) can NOT exceed 5vdc by spec. You will really still require some sort of stable 5vdc source and trying to do this with a few resistors to form a simple voltage divider may work but I don't advice it since system voltage in an automobile can vary significantly from as low as 8vdc to as high as 15vdc under normal conditions. I use a 5volt 7805 voltage regulator with proper filtering capacitors in my design so I have a solid clean 5vdc source at all times as required by the Bosch Ignitors.

The other problem is that these ignitor modules are not cheap, the Bosch OEM modules are well above $80, the discrete raw parts to create my solution run under $8 for the entire solution and it all fits into a housing the size of a 35mm film canister with 4 wires going into the housing. Of course I have significant labor to assemble and package the solution but in the end it's a properly designed solution to meet the needs of the task at hand. Basically, I do what you propose above but instead of using an ignitor to condition (reverse) the signal I use an inexpensive 2N3906 PNP transistor for that pre-conditioning stage.

I also searched for the solution you suggest on Pelican but can't find it, if you come across it I'd love to see it.

Thanks.

What's been proposed up to this point is basically the same as the original Andial design,
i.e. nothing significant there!

1. The other proposed design only requires two modules (not three) which is the case
for all other designs including the original one from Andial.
2. The DME pin 1 signal is either a ground (charging the coil) or a spike of about
350 volts and then 12 volts when the spark ends. That signal can easily be shaped
to drive the inverter module with a few resistors avoiding any need for a 5 volt supply.
The inverter module drives the second module providing the second spark, i.e. the DME
pin 1 still provides the original spark.

It's that simple!

Good discussion guys....but my wallet is ready to puke cash for a ready to use package.

Who's ready?

Dave,

Since the DME pin 1 will no longer be connected to the original coil you won't have that 350v spike in voltage. If you simply put a 1K ohm resistor to 12vdc on the output of the DME pin 1 you will have a nice clean 0.5-12vdc square wave with no significant spikes in voltage. I've done this, it was the first test I did. But the problem is that the square wave goes from 0.5vdc when coil is dwelling and 12vdc or system voltage when coil is at rest. The problem is the 12vdc system voltage is to high to feed into the ignitor. And if the system voltage was guaranteed to be stable at one constant value (ie: 14.7vdc) then a simple resistor voltage divider would be sufficient but system voltage can swing from as low as 8vdc during cranking to possibly as high as 16vdc. You can't get a proper 5vdc clamped voltage with resistors, you are going to need some sort of semiconductor device to help here. You could possibly get away with a 5volt zenner diode but a simple 7805 regulator seems more appropriate and only needs 2 capacitors to help clean thing up.

When you say 'that signal can easily be shaped with a few resistors' I disagree here. If we had a constant system voltage I'd agree but given the unstable nature of the system voltage in an automobile you could easily have a big compromise during cold cranking if battery voltage drops significantly, then the simple resistor array could fail to provide the needed 5vdc trigger and you'd have a no start.

The requirement is to take a variable 8-16vdc supply voltage and shape it to a guaranteed solid clean 5vdc supply. I don't know of anyway to do this with just resistors, you won't meet that requirements with resistors. My initial designs had been along these lines you propose but I quickly decided I needed a 5vdc solid source for reliability. Andial also has a 7805 regulator and I suspect it was for these same reasons.

I'm already building the solution for a customer so hold tight while it's finalized. I can then easily create another. I have several options in mind:

1 - You send me the 964 coil package with the coils, the bracket and the ignitor modules mounted and I create the harness and circuitry. Then you just install it in the engine bay and connect 4 simple wires!

2 - I provide the circuitry module and a wire diagram, possibly even the 2 female raw connectors and pins for the ignition modules and you create the harness and wiring from my provided schematic. This let's you mount the coils and the modules anywhere you like since you build the harness.

I'm guessing most folks will pick option #1.

You have e-mail. KTL-spider and I are both in...he doesn't know it yet, but he's in. SmileWavy

Mysocal911 is a bit of a troll to sal in many threads. Fyi.

I already said I was in two days ago :D

You have a real problem understanding a very simple description:

1. The original 3.2 coil is STILL USED and connected to pin 1 of the DME connector.
2. The additional coil is connected to one of the 964 modules with the other 964
module used as an inverter driven off of the original 3.2 coil as previously described.

How difficult is it to understand that?????????????????

That's unfortunate. And you're designing an ignition system for a 911 3.2?

And what is your contribution, please?

OK, I did not clearly understand what you had in mind, sure leave the original coil as is and then wire the additional coil as you say. That's fine.

But we still have the requirement to clamp the trigger voltage to 5vdc when triggering the Bosch Ignitor Modules. You keep saying it's simple with a few resistors. Please elaborate on this design.

A simple resistor voltage divider is all that's needed. Since you've been designing your
Andial replacement circuit, figuring the resistor values should be fairly easy.

Dave,

If we assume 15.0vdc for the resistor divider we can use a 1 to 3 ratio for the divider. Let's pick 1k and 3k in this series setup 15v->3K->1K->GND

We will have 10v across the 3K and 5V across the 1K and the world is good at 15vdc.

Now let's see what happens at 8vdc:
Same setup but now we have 2.667v across the 1K we no longer have a 5v source to trigger the BIM. That's the issue, 2.667v does not meet the spec for the trigger line on the ignitor.

Am I wrong?

Context.

Also, i will disclose to others that i am a customer of Sal's. I have his maf. I used to be a skeptic, i have learned a lot more since those days and no longer am. So that is context about me. More context is that Sal has treated me very well, and seems like a great guy with lots of knowledge. He has taught me a lot, and was always generous with information and education. Never condescending.

There are many ways to skin a cat, or find solutions to twin plugging. But if i must skin a cat, sal is a great guy to do it with. Who you are working with is important with cars.

That is my contribution.

You have not assumed the actual drive signal necessary for the module. The circuit
posted on Pelican with its resistor values indicated a functioning twin plug ignition
system while providing an adequate drive signal for the 964 module.

Note: The 5 volt spec signal mentioned is not necessarily one with a zero source
impedance/resistance.