Oscilloscope waveform interpretation - Page 1
Forum section: electronics / projects

author: Baraka
author_rank: Newbie
timestamp: November 06, 2023, 02:31:50 am
content: I am working on a project that could prove to be useful and beneficial to mankind. But I am running into some technical difficulties on how to interpret the wave forms I am getting. This forum could be the right environment to help me understand what is happening.Please find attached the screenshots from the experiments I am working on, can you make any sense of it? The blue wave is the output and the yellow one is the one that is supposed to be the switching signal to turn on and off an ignition coil. Can you suggest something to improve the switching pulse and to improve the value and strength of the output?Best regards and thanks in advance,Barak.

author: xrunner
author_rank: Super Contributor
timestamp: November 06, 2023, 02:42:06 am
content: Not nearly enough information in my opinion. Please explain in more detail the project. Are these screenshots with the switching waveform connected to the coil? What does the switching waveform look like if it's not connected to the coil?

author: Baraka
author_rank: Newbie
timestamp: November 06, 2023, 03:04:41 am
content: Thanks for your input.I am trying to use an NE555 timer to switch the primary of an ignition coil using the TIP3055 transistor. I wish to convert the generated magnetic field into something useful. The yellow waveform is the measurement at the collector of the TIP3055.I was expecting it to be some faithful reproduction of the input square waveform. But what you see in yellow in screenshot 01 is what I get on the oscilloscope, and I don't know what to make of it. The blue curve is what I get in an attempt to convert the magnetic field generated and it is also strange.Screenshot 04 shows only the blue curve alone to make it easier for someone to interpret.Can anyone make sense of all this?

author: CaptDon
author_rank: Super Contributor
timestamp: November 06, 2023, 03:36:55 am
content: I am curious how the 'output' will benefit mankind?? If you are trying to build a better ignition circuit using a 555 and your 3055 transistor you are going to be sadly disappointed. Read all about Kettering ignition circuits and associated waveforms and then look at the multitudes of capacitor discharge circuits and waveforms. I believe high voltage spark ignition is about as developed as it will ever get. I seriously doubt you will out engineer MSD or even the GM HEI and you probably won't be propelling John Force any time soon. What your waveform is showing is all of the parasitic oscillations of the typical unloaded ignition coil after the abrupt turn off of the magnetizing current. Those waveforms you see are well documented and expected and covered in detail in many books who's information would take an entire automotive engineering forum to explain.Isn't it strange that we still run magneto ignition on some of the multi-thousand horsepower engines with spark energy so high it erodes the electrodes in short order.

author: Baraka
author_rank: Newbie
timestamp: November 06, 2023, 03:46:37 am
content: Thanks for posting.Would you like to post references (links, books, etc.) to read up on Kettering ignition circuits, Capacitor discharge circuits, etc. Is it possible to concentrate those parasitic oscillations into something coherent using some circuit techniques that may be out there? Any automotive engineering books you would like to particularly recommend?Thanks.

author: jonpaul
author_rank: Super Contributor
timestamp: November 06, 2023, 07:21:25 am
content: Bonjour Monsieur Baraka: Bravo for your initiative and project.Check electroni ignition products and patents for about 70 yeas of existing work. (over 100 years old Kettering)Beware that electronic ignition coils DESIGNS are DIFFERENT than coiles for mechanical points in old auto distributors and ignition.Schematic? Photos of test setup?Your scope shots are unusable as they seem to show poor test setup, ringing from probe returns, etc.Ignition works like a flyback HV PS, it needs a current probe or CT on the coil PRI.HV secondary ignition work requires careful probing layout and triggering.e.g. the TEK P6015A 1000X 40 kV probes are very costly.Search "electronic ignition"Tektronix Circuit concepts Oscilloscope Probe Circuits book (W140, Bama archive)Bon chanceJon

author: CaptDon
author_rank: Super Contributor
timestamp: November 06, 2023, 03:02:35 pm
content: One of the more promising innovations in ignition coil spark discharge has been 'Multiple Strike Discharge'. This can take the form of 'pumping' the ignition coil circuit at its resonant frequency to keep the spark duration active long after a typical 'one shot + ring down' of the Kettering days. Another has been increasing the resonant frequency with ferrite cores instead of iron cores to get more 'sparks' in a given time period (very important when you want to spin at 15,000 R.P.M.) and with the increase in frequency it frees up time for more than one spark energy event per combustion cycle which is similar to the now popular multi injection event in diesel engines. We also see more use of the 'Wasted Spark Event' like on a lawn mower engine where there is a spark just prior to top dead center EVERY TIME the piston arrives at that position. It can provide afterburning of an air fuel charge which failed to completely burn or never ignited to begin with during the initial combustion cycle. This has a distinctive sound of a blubbering backfire in the exhaust note during engine deceleration with high intake manifold vacuum and fuel still being available. As for exactly which books to read, I gave all of mine away and they were written prior to 1970 when we were still 'admiring' dual-point distributor technology and solid state 'dwell extenders' that could give longer dwell time without burning up the points. I have recently retired as part of a locomotive engine control unit 'ECU' design team. Well, actually I retired from there TWICE! Check out some of the old Waukeshaw engines that were dual fuel diesel compression ignition WITH SPARK!!! That technology may be making a comeback with hydrogen+diesel dual fuel.

author: Baraka
author_rank: Newbie
timestamp: November 13, 2023, 02:30:48 pm
content: Thanks for your contribution.You probably could make this contribution more useful if you were to drop some links or names to google. I will try googling "Multiple Strike Discharge" with "Ignition coil" to see what comes up.Best regards,Baraka.