Hello,
I am new to the site, and am a very amateur electrician. Never tried to design a PCB or any sort of circuit for that matter so please take it easy.

With that out of the way, I am attempting to design a board that will allow me to convert a negative signal to a positive signal across 4 separate channels. I am designing this for a 4 cylinder Subaru that I am attempting to upgrade the coil packs on. The stock coil packs are a simple 2 wire setup that uses a ground signal from the igniter, which gets a signal from the ECU to fire the ignition coil. The new style is a 3 wire coil pack that has a constant 12v+ and ground, then needs a positive signal to fire, removing the igniter from the system. The only issue is that the ECU sends out a negative signal.

After doing some research I found this post: https://forum.allaboutcircuits.com/threads/converting-negative-signal-into-positive-signal.8030/
Thanks to Ron H., he provided a diagram to convert a negative to a positive for a coil pack like my own, only issue is that this is only for one coil pack. I am looking to do this for 4 separate signals for 4 cylinders. I will provide the pictures of his diagram, then what I have mocked up on EasyEDA.

If ya'll could give me some feedback on tweaks that need to be made that would be great.
Thank you,

 

I assume by negative signal, you mean the signal is negative going; that is, normally at +12V and then goes to 0V for the signal.

 

It depends on what you mean by negative and positive signal. Let's be perfectly clear here.

A negative signal could mean a signal that sits at a given voltage when in the idle state and then goes lower temporarily for a short duration. Conversely, a positive signal would pulse to a higher voltage for a short period.

Another meaning is that a negative voltage is at a voltage that is below a reference voltage. That reference voltage is commonly but not restricted to earth ground (or considered 0V reference or common ground).

Since this application refers to a trigger control signal, we still have to define the direction of the pulse, increasing in positive direction or the opposite.

To be totally unambiguous, you need to define the voltages on the low portion of the signal and the high portion of the signal.
It doesn't matter whether the pulse is positive or negative by any definition, there is an easy solution either way.

 

I assume by negative signal, you mean the signal is negative going; that is, normally at +12V and then goes to 0V for the signal.

 

I assume by negative signal, you mean the signal is negative going; that is, normally at +12V and then goes to 0V for the signal.

Thanks for the reply,
I do not believe that is the case. Its more like if you needed a negative to complete the circuit, that would be the negative "signal"

 

Thanks for the reply,
I do not believe that is the case. Its more like if you needed a negative to complete the circuit, that would be the negative "signal"

Sorry, that makes no sense to us. Can you draw a diagram to make this clearer?

 

Ba

Sorry, that makes no sense to us. Can you draw a diagram to make this clearer?

Basically, if I attach my positive lead to the ECU output, and my negative to body ground, it shows no signal. However, if I attach my negative lead to the ECU output, then put my positive lead on the 12v+ I am able to read my signal. I need my signal to be positive to the ECU output, and negative to the body ground.
Hopefully this clears some things up.

 

What do you mean by “positive lead”?
Positive lead of what?

Sorry, I don’t get it.

 

What do you mean by “positive lead”?
Positive lead of what?

Sorry, I don’t get it.

Positive lead of an oscilloscope

 

Positive lead of an oscilloscope

Ah, sorry, my oscilloscope does not have a positive and negative lead.
This could be just semantics. My oscilloscope has a signal probe and a ground.

Now, if we are talking about automotive electronics, we can talk about chassis ground. And this leads us to positive chassis systems and negative chassis systems. The auto chassis is “floating”. There is no ground on the auto, strictly speaking.

(Edit) unless the body of your car is inadvertently in contact with something that is at earth ground, for example, a jack, lift, crane or hoist.

 

And I see another problem.

If you reverse the connections between the oscilloscope and your car, you should still see the signal. You need to adjust the trigger settings on your oscilloscope.

 

You're right its just semantics. I meant positive to mean the signal hook.
And yes this is automotive electronics, and the negative side of the battery goes to the chassis.

 

And I see another problem.

If you reverse the connections between the oscilloscope and your car, you should still see the signal. You need to adjust the trigger settings on your oscilloscope.

Refer to my last post.
Also I have tested the new coil packs on the bench with a power probe. Nothing happens when I send negative to the coil pack, but when I send positive, it works. That is another reason I believe the ECU is sending out negative rather than positive.

 

Let’s make sure that we do things right.

Firstly, what is the brand and model of your oscilloscope?
Is the oscilloscope AC powered or it is a portable battery powered oscilloscope? If AC powered, is the oscilloscope properly grounded via a 3–pin cord and wall outlet?

The next step is to show that the oscilloscope works when the ground clip on the probe is connected to the negative terminal of the car battery. Then post a picture of the signal on the oscilloscope screen.

 

I hate to rain on this parade,
but the practical aspects of changing-out perfectly good Ignition-Coils for a different part-number
may be doing nothing but adding additional points of failure.

Did the Engine come from the factory with a Turbo-Charger ?,
if so, what is the stock maximum Boost-PSI ?, ( I'm guessing less than ~10-PSI ).

Are You having problems with misfiring under Boost ?

What Spark-Plug-Gap are You running ?

Are You intending to increase your maximum-Boost-Pressure ?

What makes You believe that a certain part-number of
Ignition-Coils is going to solve what ever problem You may be having, or expect to have ?

Ask people who Win Races with your same type of Engine what type of Coils they are using to win races,
also use the same spark-plugs and Spark-Plug-Gaps that they are running.
( usually "Copper-Core" Spark-Plugs gapped at ~0.035" )
( DO NOT use Platinum-Tipped Spark-Plugs on a Turbo-Charged-Engine with the Boost turned-up )

If You are not increasing Boost,
changing Ignition-Coils will do nothing but make your engine less reliable overall.

Some Coils have built-in "Dwell-Time"
Some Coils are designed to have the Dwell-Time controlled by the Engine-Computer.
If You don't know exactly what You are dealing with,
You could wind-up smoking some expensive Coils.

It's also possible to substantially alter the Ignition-Timing by changing the Coils to a different type,
this could result in reduced Power, or, severe Detonation which can easily destroy your Engine.

Don't mess around with some hack You saw on the Internet,
Look at the guys that are winning Races and copy them,
even though You probably don't need to mess with your Ignition-System at all.

If You are increasing the Boost, You must have the Engine re-Tuned on a Dyno,
or You will very likely Blow-it-up.

If You are not increasing Boost, You are wasting your time.
.
.
.

 

Nothing happens when I send negative to the coil pack, but when I send positive, it works.

You still are misusing the word "negative".
The signal only goes positive and zero in a negative ground vehicle, so I ask again, "what do you mean by negative".

 

Just so that it is made clear, there is a common misunderstanding of what positive and negative means.



On a battery, there is a positive terminal and a negative terminal and these are labelled on the side of the battery. There is no positive voltage. There is no negative voltage.

What it means is that the positive terminal is positive with respect to the negative terminal (using conventional current notation). You always need a reference point in order to assign a voltage. That is because a voltage measurement is always a voltage difference between two points.

In this case, there is 9 V difference between one terminal and the other terminal. The voltage at each terminal is unknown and can be any value. The battery is said to be "floating".

 

There is also confusion over the term “signal”. In the electronics world, a signal carries only information, not power. I believe what you are calling a signal is actually a power lead. This is important because switching a power lead is more complicated than inverting a signal.

I think this is what I think you are saying:

You have a car in which the ground connection to a coil is switched by the ECU. And you want to replace the coil with a one that needs the positive power lead switched.

Can you confirm that this is true?

 

There is also confusion over the term “signal”. In the electronics world, a signal carries only information, not power. I believe what you are calling a signal is actually a power lead. This is important because switching a power lead is more complicated than inverting a signal.

I think this is what I think you are saying:

You have a car in which the ground connection to a coil is switched by the ECU. And you want to replace the coil with a one that needs the positive power lead switched.

Can you confirm that this is true?

Yes this is true, I get what you are saying with the term signal. I guess the proper terminology is “trigger”. The switched negative lead is what “triggers” the coil packs to switch, but the new one’s require a positive trigger.
Thanks

 

I hate to rain on this parade,
but the practical aspects of changing-out perfectly good Ignition-Coils for a different part-number
may be doing nothing but adding additional points of failure.

Did the Engine come from the factory with a Turbo-Charger ?,
if so, what is the stock maximum Boost-PSI ?, ( I'm guessing less than ~10-PSI ).

Are You having problems with misfiring under Boost ?

What Spark-Plug-Gap are You running ?

Are You intending to increase your maximum-Boost-Pressure ?

What makes You believe that a certain part-number of
Ignition-Coils is going to solve what ever problem You may be having, or expect to have ?

Ask people who Win Races with your same type of Engine what type of Coils they are using to win races,
also use the same spark-plugs and Spark-Plug-Gaps that they are running.
( usually "Copper-Core" Spark-Plugs gapped at ~0.035" )
( DO NOT use Platinum-Tipped Spark-Plugs on a Turbo-Charged-Engine with the Boost turned-up )

If You are not increasing Boost,
changing Ignition-Coils will do nothing but make your engine less reliable overall.

Some Coils have built-in "Dwell-Time"
Some Coils are designed to have the Dwell-Time controlled by the Engine-Computer.
If You don't know exactly what You are dealing with,
You could wind-up smoking some expensive Coils.

It's also possible to substantially alter the Ignition-Timing by changing the Coils to a different type,
this could result in reduced Power, or, severe Detonation which can easily destroy your Engine.

Don't mess around with some hack You saw on the Internet,
Look at the guys that are winning Races and copy them,
even though You probably don't need to mess with your Ignition-System at all.

If You are increasing the Boost, You must have the Engine re-Tuned on a Dyno,
or You will very likely Blow-it-up.

If You are not increasing Boost, You are wasting your time.
.
.
.

I didn’t come here to ask about how to tune a car, I’m just coming here to check to see if my diagram looks like it would work for what i am trying to achieve.
Thanks