RegisterSearchFAQMemberlistUsergroupsLog in
Reply to topic Page 1 of 2
Goto page 1, 2  Next
RPM freakout
Author Message
Reply with quote
Post RPM freakout 
Hi,

I had previously had an issue with my CoilX board when the optical isolator fell off the board, but I was able to re-solder it and get it working. Now, I have noticed that it doesn't start showing RPM on the bluetooth display right away, but after a few minutes it seems to work. I just had my car dyno'd today and during the run, I was watching the bluetooth and it flipped out at around 4K RPM and then went away to come back later. Actually got video of it: https://www.youtube.com/watch?v=oQ9aWD2tpok

I suspect the CoilX board repair might not be great, but it seemed to be working until it flipped out.

Jake

View user's profile Send private message Visit poster's website
Reply with quote
Post  
Hi Jake, thanks for sharing the video. Do you have the coilX hooked up to the (-) of the coil pack as per the typical installation?

We're thinking about adding some "nonsense" software filters in the firmware to further help with false triggering, which is what you're seeing there. This would be added to the V2 firmware coming out shortly.

Would you have an oscilloscope to monitor the coilX input signal from the coil to observe what it's doing? We might want to get you a modified version of CoilX that might compensate for what you're seeing.

Thanks - we'll work through getting a stable reading for you!


_________________
Brent Picasso
Founder, Autosport Labs
Facebook | Twitter
View user's profile Send private message Send e-mail
Reply with quote
Post  
What I think it's doing at those upper RPMs is double triggering on the secondary pulse of the signal, shown here:
http://www.autosportlabs.net/CoilX#Theory_of_Operation

We have a 75v zener diode that/filters hides that secondary ringing from the optoisolator, if that ringing signal is extra strong in your ignition coil it could cause that false triggering. The idea would be to replace the 75v zener with a higher value, like 100v or more.


_________________
Brent Picasso
Founder, Autosport Labs
Facebook | Twitter
View user's profile Send private message Send e-mail
Reply with quote
Post What if ignition coil ground is permanently connected? 
Since Jake has a Porsche 3.2 Carrera (I am guessing from the wiring diagram in another discussion), his CoilX can be connected just as the diagram shows - to the coil negative. Because in that ECU equipped car the coil is grounded through the ECU. Which should mean it has current running through it, and then not running through it, and so on, and looks just like the website CoilX wiring diagram.

It turns out (I had to look all this up) that early Porsche 911s with points, but just a 12V spark coil, have the coil ground running through the points. So I am assuming that the CoilX would work with that setup also.

However, from the early 1970s through 1983 Porsche 911s use a Capacitative Discharge Ignition (or System). When the ignition is in the run or start position, the 450 volts the CDI box )puts out is always present at the + terminal of the spark coil. The spark coil ground/- terminal is hard wired to engine/chassis/battery ground.

I hadn't realized this when I went to a friend's house to test my CoilX. I am using it to feed engine revolution (not RPM) signals to a microprocessor, which collects 15 seconds worth, and then sends that count to a spreadsheet on a laptop. My attempts at using a inductive clamp on one of the high tension wires produced inconsistent signals with the circuit some electronics buffs suggested to me. And I believe that some data collection systems have had issues with using inductive sensing from the coil or plug wires also. So your CoilX seemed like a solution to my problems.

Until I noticed a nice wire from the coil negative to an engine ground about 4" away. I hooked up to it anyway, butI was not surprised to see that the microprocessor was not collecting counts. How could it? Hooking ground to ground ought not to do anything. I was scared to hook from the + (which gets 450V) to ground even though I know your design strips off the low voltage, then beats the result about the head and shoulders until it is a nice square (which I don't need) 5V signal (which I do need).

I have an ancient scope, but didn't think I was going to need it so didn't bring it along. I'm not that good with it anyway.

So how do you suggest I connect the CoilX where the negative side of the coil is permanently grounded? I couldn't find a post discussing this configuration, but maybe I'm not good with search terms.

Regards
Walt Fricke

View user's profile Send private message Send e-mail
Reply with quote
Post  
Hi Walt,

To really understand what you're working with you will need a scope to visualize the waveforms coming off of the coil - you can probe both sides of the ignition coil to see what you can get. If you can, take pictures of the scope and post them here and we can help come up with a reliable way to get a clean RPM signal.

Is the ignition system OEM? what wire feeds the dash tachometer and where is that connected to on the ignition system?


_________________
Brent Picasso
Founder, Autosport Labs
Facebook | Twitter
View user's profile Send private message Send e-mail
Reply with quote
Post  
Brent - thanks for the quick reply.

This is OEM. I don't want to use the tach signal because hooking up very quickly, then unhooking and going on to check the next car, is very important.

From some research I did (Christopher Jacob's book on ignitions) it appears that make/break (or the equivalent) of the positive input to the spark coil is an inherent characteristic of CDI ignitions. I suppose those are usually discarded when switching to computer controlled ignition. So I was supposing you had a generic solution for that kind of ignition, though I suppose no cars come with it any more.

It will be a while before I can get oscilloscope traces, but if those are needed I'll get them. My knowledge of electronics is more of the cookbook and soldering level, with a rudimentary understanding of what components do or don't do - not up to the level of designing analog circuits.

View user's profile Send private message Send e-mail
Reply with quote
Post  
Well, we do have the Megajolt crank fired ignition, wich will be a pretty dramatic upgrade in it's own right - tunability, power in smoothness. That system offers a few different clean tach output options as well.

Keep us posted on the measurements!


_________________
Brent Picasso
Founder, Autosport Labs
Facebook | Twitter
View user's profile Send private message Send e-mail
Reply with quote
Post  
Brent

Here is an oscilloscope trace of the positive terminal of the spark coil used with a capacitative discharge ignition system, where the negative side is permanently grounded. The EE who took this had this to say about interpreting it:

Below are the ‘scope screen captures of Drew’s 911SC CDI ignition primary signal. Since I used a 100:1 input voltage divider, the voltage scale is 100X larger than shown to the right of the waveform.

•The vertical scale is 100V per major division.
•The horizontal (time) scale is 20uS per major division.
•Zero volts is slightly offset at 0.25 divisions above the center line (because I didn’t auto-cal the scope at the shop)
•Thus the main pulse is a -300V pulse that falls sharply, then rises to +120V nearly linearly over 20uS.

My EE friend thought that perhaps the peak signal could be that high, but beyond the resolution of his scope at the settings used. One of the characteristics of a digital scope, I gather. He tried to get a train of pulses to examine, but for some reason could not get ones with useful height.

Will the CoilX work its electronic magic on a signal like this? How about if the signal is the 460 volts Porsche lists in its shop manual?

I need a 3-5V signal I can use to count engine revolutions for testing transmission gear ratios for rules compliance. Your CoilX should work just fine for the various models which use the ECU to ground the spark coil. On the OBD cars I can get the spark signal from the OBD port. But these CDI models, from 1969 through 1983, are very popular as race cars in a "stock" class, so they are now the last piece of the puzzle.

What do you think?

Walt Fricke

View user's profile Send private message Send e-mail
Reply with quote
Post  
Thanks for that. The CoilX module might work; if you look at the theory of operation here http://autosportlabs.net/CoilX It shows how it will clip everything below 75v, and it also will block the reverse pulse as well. If 75v clip is too low, we could try a 100v clip to only trigger on the peak of that flyback pulse.


_________________
Brent Picasso
Founder, Autosport Labs
Facebook | Twitter
View user's profile Send private message Send e-mail
Reply with quote
Post  
The large spike is negative, isn't it? Or is that an artifact of a scope setting? The goal is to have only one signal come out of the optoisolator I gather is at the other end of the circuit, and is what makes sure only a 5V or smaller signal comes out.

Is the flyback pulse the positive "ringing" after the larger negative pulse?

How would I raise the 75V threshold to 100V?

If the input leads were reversed, would the large spike be seen as positive? Then all of the ringing would be seen as negative and discarded?

The Schmidt trigger squares things up, though for the microprocessor where the signal will be counted that apparently isn't all that important, though it doesn't hurt. On getting a voltage the microprocessor stores it as a count, and also waits for a set time to look for another count. In my application we are looking at 800-1500 rpm. Even at three counts per revolution, that is a low frequency so using software to filter I gather is a good technique.

And I plan to use the CoilX on a number of Porsche models which have the ECU ground and open the coil primary negative, as in the traditional Kettering ignition - the 944s being a family which all have an ECU do this, and the 1984-89 3.2 Carreras being another. It would be convenient if I didn't need one CoilX for one use, and another for another.

View user's profile Send private message Send e-mail
Reply with quote
Post  
Yes, that's the flyback pulse. There's a Zener diode that clips the signal at 75v. Changing it to 100v means using a different part. We've been thinking of altering the design to just use the 100v part since all of the coil flyback signals we've seen exceed 100v.

Re: reversing the leads - which coil terminal did you probe again? see what the signal looks like for each terminal on the coil pack.


_________________
Brent Picasso
Founder, Autosport Labs
Facebook | Twitter
View user's profile Send private message Send e-mail
Reply with quote
Post  
We probed the coil positive. The coil negative, when probed (we were initially uncertain which was which, as the coil was mounted on the car, faces sort of down, and has a rubber protective cap over it), didn't seem to show much, if anything. I wouldn't have expected anything, since it is hard wired to ground, but you know more about that kind of thing than I do.

On this Bosch coil positive is indicated by an A. The coil negative is indicated by a minus sign. At least looking with a mirror showed these. The A might have also had a plus, and the negative a B. Other Bosch coils have 15+ and 1-, as well as a 4 to indicate the secondary spark wire to the distributor, all under the standard German wiring numbering system.

View user's profile Send private message Send e-mail
Reply with quote
Post  
Brent - I tried the CoilX on a Porsche 911 3.2 liter Carrera. It uses the ECU to open and close the ground of the coil. The first data capture worked perfectly. But thereafter the data was junk - lots of missing counts. Attached are a scope picture, and - if it will send - a video. Oh, oh - file too big for video. Color me baffled, as while the CDI system has mysteries, the ECU control should be much like Kettering designed, just electronic "points" so to speak.

View user's profile Send private message Send e-mail
Reply with quote
Post  
Hi Walt - thank you. Got a link to a better version of that picture? It's kind of hard to see. Video link would be good as well.

-Brent


_________________
Brent Picasso
Founder, Autosport Labs
Facebook | Twitter
View user's profile Send private message Send e-mail
Reply with quote
Post  
Following this still. I now get consistent RPM indication with the new 2.7.7 firmware but I noticed today while testing that I still have the RPM freakout situation. I saw the revs go up as high as 3800 or so, but above that they went to 400000-something, which even the '86 Carrera is not capable of, sadly.

I have an autocross coming up this weekend and I'm leaving for Sebring tomorrow for the 48 hours club race, so I don't have time to mess with it, but I still need a solution.

I never got the 100V zener, but I do have a reflow oven controller and a new toaster oven now if I need them. Smile

View user's profile Send private message Visit poster's website
Display posts from previous:
Reply to topic Page 1 of 2
Goto page 1, 2  Next
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You cannot download files in this forum