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Topic: EMI from small engine freezing up the arduino (Read 575 times) previous topic - next topic


Jan 13, 2021, 05:33 pm Last Edit: Jan 13, 2021, 05:34 pm by Paul_KD7HB
Is it even known how these extra signals get in the Arduino?  Should I be looking at the ground pins or the other pins?  I've tried those iron clamp on things they didn't do any good.
Every wire in your machine will act act like an antenna to transmit RF at all frequencies when it carries a sudden pulse of current. The greatest RF power transmitted will be when the particular wire is 1/4 wave length for some frequency.
Any wire in your machine will RECEIVE those RF impulses, just like your AM/FM radio or cell phone does.
If the wires connect to something that is sensitive to those RF impulses, like your Arduino, then they will cause problems.
The cure is to not allow the RF pulses to be transmitted in the first place. When that is not possible or practical, then the sensitive equipment MUST be shielded from the RF pulses. And all wire connecting to the sensitive device must be shielded from the RF pulses. That is why a metal enclosure is required. That is why shielded wire is required, whit only the Arduino end of the wire connected to ground. That is why your metal enclosure must be connected to the common ground of the device it is placed in. When all the shielding fails, then small value capacitors are added to wires to short the RF impulse to ground.


Is it even known how these extra signals get in the Arduino?  Should I be looking at the ground pins or the other pins?  I've tried those iron clamp on things they didn't do any good.
  • Unused pins left floating? I suggest configuring all unused pins with INPUT_PULLUP.
  • Any relays nearby? Yeah, lots of suggestions for improvement here ... opto isolation, separate power source,relays further away in a separate case, relay contact arc suppression, ferrite cores, etc.
  • EMI/RFI Shielded Extruded Aluminum Enclosures (many others available)


Hey Paul, I never said my problem was EMF or mentioned it. I  do know the difference and why I clearly stated EMI from the motor ignition freezing the Arduino.

Your suggestion to cover the spark plug and wire with copper tubing is a bad idea. That would actually damage the ignition system and cause the points to wear out faster then the cam.

Regardless. I've decided to change things up and found a metal box actually designed for electronic test equipment. It's large enough to house the mechanical and electronics instead of the 2 containers. I also bought 2 die cast aluminum cases at the electronics shop to house the Arduino and motor drivers. I learned that's its better to use  parallel over series grounding back to battery. Not to mix the signal grounds with other grounds
I ordered clamp on ferrite beads to attach to every wire and cable penetrating the box.

Starting the project last year, I didn't even know what an Arduino was. It's been one hell of a learning experience.


Jan 14, 2021, 03:56 pm Last Edit: Jan 14, 2021, 05:09 pm by Paul_KD7HB
No you didn't. but the person trying to hijack your thread did.

Added later: Actually, I have owned two AC generators that had the spark plug wires in pipes for shielding. One was a two cylinder Wisconsin engine. The other was a two cylinder Lycoming engine. Neither produced any RFI that I could detect.


Jan 14, 2021, 06:38 pm Last Edit: Jan 14, 2021, 06:46 pm by raschemmel
No you didn't. but the person trying to hijack your thread did.
Quote from Sevenoutpinball:
How does EMF cause these problems in the first place and would it help to put the Arduino in a lead lined box and to that solder the shielded cable that goes to the Arduino?




The smartest person can make the dumbest mistake.


did I say something wrong?
You hijacked a thread dealing with EMI problems from an engine ignition and interjected EMI problems form a pin ball machine. Totally different EMI sources and totally different EMI solutions.
EMI problems are solved by minimizing the source of the problem.


If I were to build such a device I would create a shield for every wire as it entered the "housing".

One way to do this is to have a copper board with the copper grounded, holes for each wire and a capacitor from each wire to the copper plane.

The key is to:

1) filter every wire (the incoming ground wire can be connected directly to the copper plane.
2) keep the leads of the capacitor (0.01µf, no larger) short.   Electrical noise is like smell, once it gets in it goes everywhere.

I don't know if the aluminum foil is adequate.  If filtered properly I've created designs with plastic covers albeit much smaller devices.  These designed passed automotive electrical noise (both in and out) requirements and some were located under the hood of a vehicle.

Please do not PM me with thread based messages.  If your thoughts are worth responding,  the group should benefit from your insight.


Hi Paul,

Wonder if you're still monitoring this thread.

I had a tech come and put a scope on my system. He found EMI was causing intermittent voltage spikes coming in from the ground. (up to 10.3 volts)

Tried chokes on the Arduino's linking board ground and the Arduino power input ground. That brought the spikes down, but didn't eliminate them. It would work for about 10 minutes then freeze up again.

He then made a recommendation to try out. I went the next day, bought the $4.00 part, installed it, and Voila, problem solved. I drove the remote control snow blower around for an hour without any more problems.

I hope you're listening as I post the answer here.

My motor had a regular spark plug. Problem solved using a 4.00 resistor type spark plug.


I have not thought about resistor spark plugs or resistors to go between the wire and the spark plug or even the resistor wire we used to install. Had such on my 1950 Mercury!
Glad you have eliminated the noise.

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