How can I shape, and make use of, pulses induced into a coil by spark plug wire?

[potoole64]

How can I shape, and make use of, pulses induced into a coil by spark plug wire?

I wrapped 4 loops of #22 insulated wire around a sparkplug wire on a motorcycle, then connected the looped wire ends to an oscilloscope. From this setup, the scope showed large, very ragged, pulses being induced into the loop. The pulses are larger than I expected, very irregular and appeared to be composed of more than one pulse.

I would like to feed those pulses to a data logger (already made) that will count and store those pulses as 'pulses per second'. Eventually used to determine RPM in PC program.

I think the pulses, as they are directly obtained from spark plug wire, would be difficult to work with, and that they should be shaped into something more useful.

Can anyone suggest circuitry to shape and form those ragged pulses?

I’m thinking:
Filtering, rectifying, clipping, clamping , integrating ?
Has anyone worked with such a thing?
How about optical circuitry?

I made a data logger, using Arduino system, that stores data on SD cards. I made it to accept, count and store square wave pulses. I can use the stored SD data and transfer it to a PC program, such as a spreadsheet.

Thank you
PO’T

 

[Hero999]

Are you capacitively or inductively coupling the energy?

Are both ends of the wire connected to the logger or is only one end connected?

As it's high voltage then I'd recommend capacitive coupling which only requires one end to be connected.

Ideally the 0V rail of the data logger should be connected to the motorcycle chassis but it might work even if it isn't.

The input to the datalogger should be protected against high voltage spikes which may already be the case. If not clamping diodes should be fitted between the input and the logger's PSU or a zener could be used.

 

[MikeMl]

Look at these previous threads:

one

two

 

[potoole64]

Hero999
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Are you capacitively or inductively coupling the energy?

Are both ends of the wire connected to the logger or is only one end connected?

As it's high voltage then I'd recommend capacitive coupling which only requires one end to be connected.

Ideally the 0V rail of the data logger should be connected to the motorcycle chassis but it might work even if it isn't.

The input to the datalogger should be protected against high voltage spikes which may already be the case. If not clamping diodes should be fitted between the input and the logger's PSU or a zener could be used.

I haven't tried connecting the pulses to my Arduino Logger. Not until I've improved the pulses. I've only tested my makeshift coil assembly with an oscilloscope, just to see what I would get.

Previously, I've collected pulses from the motorcycles speed sensor, by attaching the output of the sensor to the arduino logger by the use of a voltage divider. The sensor pulses are 12v; arduino requires 5v input. The sensor pulses are neat square waves, and are developed from gears in the transmission. Engine RPM can be calculated if one knows the bike's gear ratios, and if the number of pulses per second per vehicle speed can be judged.

RPM can be more directly measured from ignition pulses. Its possible to collect ignition pulses directly from the output of the electronic ignition system. Those pulses, however, are also very ragged as they are used as the direct input to the ignition coil. I've used that source before, but the ragged pulses resulted in high inaccuracy, and other problems, and I was concerned about possible negative affects on the electronic ignition system. I thought that using the pulses inducted into my sparkplug loop would be more passive, and less likely to cause problems with the ignition system.

Cruising down a highway, many miles from nowhere, and having the ignition system poop out is not something an old biker looks forward to.

Thank you
PO'T

 

[potoole64]

MikeMl
Look at these previous threads:

one

Mike,
Your circuit in thread 'one'(https://www.electro-tech-online.com/threads/triggered-monostable-multivibrator.103177/)
looks interesting. I won't be coming off of the ignition output, which is the input to the primary side of the ignition coil (xfmer), and is also used as the input to electronic tachometers(my bike didn't come equipped with one).

My ignition is electronic, not the old points and 'condensor' type. I've messed with the output a few times; the results weren't satisfactory. Feeding those messy pulses directly (via volt divider) to a microcontroller-datalogger resulted in very inaccurate counts, and I was concerned about causing problems with the electronic ignition.

I read through those two threads, (Mikes)what was the final consensus?

 

[Hero999]

Have you looked at the waveform on a 'scope?

It's possible just clamping it to the power supply will be enough to square the waveform.

 

[MikeMl]

Mike,
...

I read through those two threads, (Mikes)what was the final consensus?

I have used my circuit on aircraft magnetos, old cars with point ignition, and modern CDI systems.
Grab a scope with 10x probe and go looking around the spark controller.

 

[potoole64]

MikeMl and Hero999,
Thanks for the advice. Both have given me a good plan. I will try using Mikes ckt, as well as the looped wire, clamped to power supplies. I'm not sure if I need to clamp to the motorcycles 12v supply, but I will need 5v for the arduino datalogger. All circuitry should probably be connected to motorcycle ground.

Mike, where can I find the shielded cable? Radio Shack? I have several lengths of shielded cable left over from the cable tv company. Some of it was used for internet connections.

 

[Hero999]

You should clamp to the 5V power supply with diodes so the datalogger isn't damaged by high voltage spikes.

 

[MikeMl]

The shielded cable is nothing special. I used some miniature Teflon Coax cable I had around. Avoid the RF coax that uses polyethylene as the center-conductor insulator because it has a very low melting point. The so called "plenum" cables are better. The primary purpose of the shielded lead is to prevent RFI radiation that could get into your radio(s) (the last thing you want if you are a ham radio operator or own an aircraft).