From: Jason White <whitewaterssoftwareinfo@gmail.com>
To: Microcontroller discussion list - Public. <piclist@mit.edu>
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Date: Wed, 30 Dec 2020 16:36:47 -0800
Subject: Re: [EE] Eliminating external noise through PS
Thread-Topic: [EE] Eliminating external noise through PS
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Have you considered using the "poor man's" differential probe "trick" [1]
to assess (partially) if the noise is being picked up by your leads?

[1] https://www.eevblog.com/forum/beginners/poor-mans-differential-probe/



On Wednesday, December 30, 2020, Neil <picdude3@narwani.org> wrote:

> Hmmm... not a current clamp, but I probably have a current sensor. Only
> thing is that it would most probably be a high range (few 10's of amps
> at least).
>
> I really need to research and get some better equipment one of these days=
..
>
> Cheers,
> -Neil.
>
>
>
> On 12/29/2020 5:30 PM, Bob Blick wrote:
> > Hi Neil,
> >
> > I've found that measuring current is quite often better than measuring
> voltage when seeking out noise problems. I can be less convenient to do b=
ut
> at least where wires enter and exit the board it can be quite useful. Do
> you have a current clamp you can attach to your scope?
> >
> > Cheerful regards, Bob
> >
> > ________________________________________
> > From: piclist-bounces@mit.edu <piclist-bounces@mit.edu> on behalf of
> Neil
> > Sent: Tuesday, December 29, 2020 10:20 AM
> > To: Microcontroller discussion list - Public.
> > Subject: Re: [EE] Eliminating external noise through PS
> >
> > Happy holidays everyone.
> >
> > Okay, I got back to this recently and have a bunch of updates:
> >
> > For the tl;dr 'ers... I've got a lot of noise out, the processor does
> > not crash anymore, but 2 questions remain:
> >
> > - Should I have the AC-outlet ground wire, coming onto the PCB and used
> > as a shield?
> >
> > - If I hold the AC wire with my hand, the noise (as seen on the
> > oscilloscope) drops (noticeably).  Shielding the AC wire does not have
> > the same effect, so what is happening here, and how can I use this to
> > help reduce the noise even more?
> >
> >
> > For the gory details, here's my summary of what I tried and found...
> >
> > For reference...
> > http://orlandorobotbuilders.com/stuff/SMNoise/20201224-SMN-08.jpg , and
> > noise is mostly in the few Mhz range and higher.
> >
> > - Ceramic cap across (DC) motor wires (right at the motor) helped a bit=
..
> > - Low-pass filter helped minimally
> > - Pi filter was a bit better, but still small impact.
> > - Common mode choke (uncalculated, but should've been able to separate
> > 60Hz from Mhz-range noise) didn't help.  I am new to these, but
> > apparently above some frequency the impedance drops again.
> > - Ferrite across AC side of motor wires helped minimally.
> > - Ferrite on incoming-power AC wires did not help
> > - Removed relay (and jumper across contacts to run the pump) to see if
> > noise was coming into board from that side, but nope.
> > - Started from scratch with a minimal setup -- the AC-DC PS (no PCB),
> > with wires soldered on for the incoming power and parallel wires to run
> > the pump, and a 1k load resistor on the PS output. Still a lot of noise
> > - Low-pass filter again helped reduce noise minimally.
> > - Capacitance multiplier helped noticeably.
> > - 2 more ceramic caps from each motor wire to ground/motor case (right
> > at the motor) helped noticeably.
> > - Twisted the AC wires to the motor tighter, and didn't really see any
> > difference.
> > - Back to original board, to use some of these, but too much voltage
> > drop on capacitance multiplier to be usable.  I should calculate this
> > properly and find the right transistor for this.
> >
> > At this point, I have 3 @ 0.01uf ceramic caps at the motor and the pi
> > filter and the board isn't crashing, but I can still see some noise on
> > the scope, which I'd like to reduce even more.  Going to try a
> > multi-stage pi/LC filter.
> >
> > But I'm curious how to use the "phenomenon" where holding the AC wire i=
n
> > my hand reduces noise noticeably, to help this.
> >
> >
> > Thanks,
> > -Neil.
> >
> >
> >
> > On 12/13/2020 7:15 PM, Neil wrote:
> >> That's a definite possibility at this point.  The original circuit
> >> (prior version) worked great with 2 layers, but I needed 2oz copper to
> >> handle the pump current.
> >> Never version works just as great.  Or  I should say "worked", until
> >> they decided to switch from the AC pump to this DC pump.
> >>
> >> Cheers,
> >> -Neil
> >>
> >>
> >>
> >> On 12/13/2020 6:58 PM, Jason White wrote:
> >>> Neil, from the pictures it looks like you're using a 2 layer PCB. Hav=
e
> you
> >>> considered a 4 layer PCB? A continuous dedicated ground plane layer
> would
> >>> drastically reduce the loop area (and thus susceptibility to EMI) of
> your
> >>> traces.
> >>>
> >>> Otherwise, it may be worth considering moving the relays to a separat=
e
> >>> board/area.
> >>>
> >>> On Sunday, December 13, 2020, Neil <picdude3@narwani.org> wrote:
> >>>
> >>>> I strongly feel so, because in my early tests, I:
> >>>> (a) disconnected one of the pump wires (so the pump wouldn't run), a=
nd
> >>>> it was (expectedly) very clean (on the scope).
> >>>> (b) disconnected both of the pump wires and plugged it into the fema=
le
> >>>> side of a PC power cord, so the pump ran, but was connected to 120VA=
C
> >>>> from a different source.  Very clean power again.
> >>>> In both cases, all else stayed the same including where the wires we=
re
> >>>> draped, etc.
> >>>>
> >>>> In other tests, I moved the scope, power lines, etc and no change to
> the
> >>>> noise on the line.
> >>>>
> >>>> Either way, I haven't done my other tests yet since I took the pump
> with
> >>>> me, so I'll get to those this week.
> >>>>
> >>>> Cheers,
> >>>> -Neil.
> >>>>
> >>>>
> >>>> On 12/11/2020 7:37 PM, Jason White wrote:
> >>>>> Hi Neil,
> >>>>>
> >>>>> This may be a silly question: are you sure that some of these volta=
ge
> >>>>> spikes that you've captured on the scope are not artifacts of your
> >>>>> measurement setup? The loop formed by the ground wire/clip on a sco=
pe
> >>>> probe
> >>>>> makes a very effective antenna. Maybe your power rail is cleaner
> than you
> >>>>> think - in which case the true problem might be elsewhere.
> >>>>>
> >>>>> -Jason White
> >>>>>
> >>>>> On Fri, Dec 11, 2020 at 3:11 PM Neil <picdude3@narwani.org> wrote:
> >>>>>
> >>>>>> Sorry, disappeared for a couple days, but some quick answers to
> >>>>>> everything for now, and my next steps:
> >>>>>>
> >>>>>> - Yes I have flyback diodes.   Highlighted with yellow here,  just
> above
> >>>>>> the relays...
> >>>>>> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-06.jpg
> >>>>>> - James & Russell, in that diagram also, I labeled the paths for
> power.
> >>>>>> The 5V to the relays is pretty much dedicated and 5V is on the top
> >>>>>> layer, and (dedicated) ground for the relays on the bottom layer.
> But
> >>>>>> yes, it's right up against the AC section, but as many components
> have
> >>>>>> been removed now, I will push that far away.
> >>>>>> - The 3.3V regulator has been getting a bit warmer than I like, so=
 I
> >>>>>> have been planning to use a buck converter instead.  But maybe I
> should
> >>>>>> run two 3.3V regulators instead?  I would think that the buck
> converter
> >>>>>> would be pass less of the noise through.
> >>>>>> - I ran over there quickly to pick up stuff and tried a crude
> >>>>>> (uncalculated) common-mode choke I made up from stuff I could find=
..
> Did
> >>>>>> not make in dent in the noise coming through.
> >>>>>> See here...
> >>>>>> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-07.jpg
> >>>>>> - I feel like Brent may be correct, that the noise may be coming
> from
> >>>>>> the relay side.  The processor (ESP32) is resetting.  I know it's
> not a
> >>>>>> firmware issue as it had zero crashes with the previous pump.
> >>>>>>
> >>>>>>
> >>>>>> Adding some info:
> >>>>>> The previous pump was a huge AC pump.  This new pump is actually
> DC, but
> >>>>>> there's a bridge rectifier on the wires.  So I'm now convinced tha=
t
> the
> >>>>>> noise is coming from brushes.
> >>>>>> I brought the pump with me, and I have a new blank board.  My plan
> is to
> >>>>>> reproduce just enough of the circuit to see the noise, and I can
> cut and
> >>>>>> re-route traces (the 5V & ground to the relays) to see if helps.
> >>>>>> I will also add a ceramic capacitor to the pump wires (right at th=
e
> >>>>>> pump), and hope that helps.  Plus twist the wires.
> >>>>>>
> >>>>>> I'll be back with some results.
> >>>>>>
> >>>>>> Cheers,
> >>>>>> -Neil.
> >>>>>>
> >>>>>>
> >>>>>>
> >>>>>> On 12/10/2020 7:28 PM, FTL wrote:
> >>>>>>> This is almost too obvious, but in the schematic I do not see a
> flyback
> >>>>>>> diode across the relay to suppress the back EMF when the relay is
> >>>> turned
> >>>>>>> off. The lack of diode would cause a serious spike in the 5V supp=
ly
> >>>> when
> >>>>>> the
> >>>>>>> relay is turned off.
> >>>>>>>
> >>>>>>> Is the transistor being turned on hard enough to keep the relay o=
n
> >>>>>> properly.
> >>>>>>> If it is not fully on with no flyback diode, maybe it is
> occasionally
> >>>>>>> releasing and causing big noise on the 5V bus.
> >>>>>>>
> >>>>>>>> -----Original Message-----
> >>>>>>>> From: piclist-bounces@mit.edu <piclist-bounces@mit.edu> On
> Behalf Of
> >>>>>> Neil
> >>>>>>>> Sent: December 8, 2020 11:04 AM
> >>>>>>>> To: Microcontroller discussion list - Public. <piclist@mit.edu>
> >>>>>>>> Subject: [EE] Eliminating external noise through PS
> >>>>>>>>
> >>>>>>>> Hi,
> >>>>>>>>
> >>>>>>>> I'm working on a device that takes 120VAC, converts to 5VDC with=
 a
> >>>> PCB-
> >>>>>>>> mounted power supply, then further reduces that to 3.3VDC with a
> >>>> linear
> >>>>>>>> regulator.
> >>>>>>>> A 3.3V microcontroller switches a relay to power a 120VAC pump.
> >>>>>>>> Overview...
> >>>>>>>> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-00.jp=
g
> >>>>>>>>
> >>>>>>>> All has been great until we switched to a specific pump, which
> happens
> >>>>>> to
> >>>>>>>> generate a LOT of conducted noise, which passes through the 5V
> PS, and
> >>>>>> the
> >>>>>>>> 3.3V regulator, and causing the microcontroller to crash.
> >>>>>>>> I did a bunch of tested and found that the noise is being
> conducted
> >>>>>>> through
> >>>>>>>> the wires back to the board through the PS, through the linear
> >>>>>> regulator,
> >>>>>>> and
> >>>>>>>> this is the 3.3V line...
> >>>>>>>> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-01.jp=
g
> >>>>>>>>
> >>>>>>>> I was over at someone else's place so did not have a lot of part=
s
> with
> >>>>>> me,
> >>>>>>>> but...
> >>>>>>>> Adding a bunch more 0.1uf bypass capacitors all over the board
> did not
> >>>>>>> help.
> >>>>>>>> Changing the power supply from an IRM-10-5 (industrial spec, 200=
mV
> >>>>>>>> ripple) to MPM-10-5 (medical spec, 100mV ripple), helped reduce
> the
> >>>> rate
> >>>>>>> of
> >>>>>>>> the crashing... but the ripple itself wasn't causing crashing.
> >>>>>>>>
> >>>>>>>> Adding (non-specific size) ferrites to the pump wires, and 120VA=
C
> >>>> input
> >>>>>>> wires
> >>>>>>>> did not help.
> >>>>>>>> I then tried to create a crude/uncalculated LC filter (which
> whatever
> >>>>>>>> components I had on hand (33uh inductor and 1000uf capacitor,
> should
> >>>> be
> >>>>>>>> low ESR), then a Pi filter (added 680 uF capacitor), and those
> barely
> >>>>>> made
> >>>>>>> a
> >>>>>>>> dent.
> >>>>>>>> Eventually I added another 0.1uf capacitor to the output side of
> the
> >>>> pi
> >>>>>>> filter
> >>>>>>>> and that helped enough to prevent the microcontroller crashing.
> >>>>>>>> But there is still a lot of noise on the 3.3V line...
> >>>>>>>> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-02.jp=
g
> >>>>>>>> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-03.jp=
g
> >>>>>>>>
> >>>>>>>> FWIW, this is where it ended up...
> >>>>>>>> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-04.jp=
g
> >>>>>>>>
> >>>>>>>> The noise is in the 7Mhz to 30Mhz range (prob even higher).
> >>>>>>>> I feel like smaller, low-ESR ceramic caps should help, but I
> doubt it
> >>>>>> will
> >>>>>>> take
> >>>>>>>> out most of the noise.
> >>>>>>>> What is the right type of filter to eliminate this noise?
> >>>>>>>>
> >>>>>>>> Cheers,
> >>>>>>>> -Neil.
>
> --
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--
Jason White
--
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