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EMI

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I'm beginning my foray into electronics with no formal education, so I'm a complete hacker.

I'm designing circuits with microcontrollers, stepper motors and lighting and I'm thinking ahead a bit and trying to account for possible EMI.

I've read about the two forms of EMI radiated and conducted but I'm not sure about anything past this. Websites I've seen generally describe what it is and general classes of sources of the stuff, but I'm not sure how to move on from the basics. I don't have an oscillascope, but even if I did, I wouldn't know what to point at what.

1. The question that I currently am trying to solve is power over ethernet... and the obvious EMI potential from running data along side power.

I found this: https://e2e.ti.com/support/power_management/power_interface/f/204/p/193984/693040

The first response post has two links but I couldn't find anything useful in them - bit too advanced.

2. ICs - I'm reading that even they can be sources of EMI and given how thin some traces can be, how do you make sure your design won't get affected?

3. DC lighting circuits, are these potential sources for EMI?

4. How do you detect EMI? Say I have a stepper motor, how do I go about detecting how far away you need to be away from it and its cabeling?

5 Is there some best practice for designing for EMI?

Hopefully someone can point me in the right direction.
 

DerStrom8

Super Moderator
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If you are serious about learning about this stuff, invest in this:

If the user isn't a logged-in member at AAC he or she will not be able to view your image. I recommend uploading it to ETO instead.
 

joeyd999

New Member
Like any noob, I guess I've got a few things to learn:

20171122_182714.jpg
 

joeyd999

New Member
2. ICs - I'm reading that even they can be sources of EMI and given how thin some traces can be, how do you make sure your design won't get affected?
Trace width has no bearing on EMI generation/susceptibility. Low impedance switching nodes generate EMI, high impedance nodes capture it.

3. DC lighting circuits, are these potential sources for EMI?
Switched mode circuits, yes. DC circuits, no.

4. How do you detect EMI?
With very specialized and expensive equipment. Or an AM radio.
 

cowboybob

Well-Known Member
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Generally speaking, EMI will be produced from any conductor that has a variable voltage potential, however produced. Thus, any device that is not 100% DC will generate EMI. For instance, a conventional incandescent bulb type flashlight produces zero EMI.

That said, during the circuit design stage for your projects, I would not concern myself with EMI issues. There are a myriad of ways to reduce EMIs during the component/connections/comms layout phase.

The question that I currently am trying to solve is power over ethernet... and the obvious EMI potential from running data along side power.
CAT5 cabling (ordinarily used with wired Ethernet connections) usually eliminates EMI issues.With no more that your brief description of your circuit:
4. How do you detect EMI? Say I have a stepper motor, how do I go about detecting how far away you need to be away from it and its cabeling?
I'd venture that any EMI produced will be inconsequential.

What sort of device do you think might be affected?
 

dr pepper

Well-Known Member
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2 large causes of Em interference are high frequency unshielded circuits such as a 1mhz oscillator, it will radiate to some extent depending on layout a 1mhz signal, and then third harmonics so 3mhz 9mhz 12mhz etc the amplitude drops with each increasing harmonic.
Then there are circuits with rapidly changing voltages, if a pulse generator has a sharp 'edge', ie looking on a 'scope the voltage rises very quickly, or goes from zero to some voltage in a very short time that will also generate some interference, and if the circuit isnt well designed it can cause resonance or ringing within the system worsening the effect.
As well as radio wave interference there is magnetic field interference this is more apparent at higher power levels.
Em interference issues can get really complicated, try not to get bogged down with stuff like that, I only address issues as they arise, if you follow cat5 practices you shouldnt have much trouble.
 
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