From: David VanHorn <microbrix@gmail.com>
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Date: Tue, 29 Dec 2020 14:13:52 -0800
Subject: Re: [EE] Eliminating external noise through PS
Thread-Topic: [EE] Eliminating external noise through PS
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What's your reset circuit look like?   High enough impedances here can
cause these problems.

On Tue, Dec 29, 2020, 11:22 AM Neil <picdude3@narwani.org> wrote:

> 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 in
> 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. Have
> 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 separate
> >> 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), an=
d
> >>> it was (expectedly) very clean (on the scope).
> >>> (b) disconnected both of the pump wires and plugged it into the femal=
e
> >>> side of a PC power cord, so the pump ran, but was connected to 120VAC
> >>> from a different source.  Very clean power again.
> >>> In both cases, all else stayed the same including where the wires wer=
e
> >>> 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 voltag=
e
> >>>> 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 scop=
e
> >>> probe
> >>>> makes a very effective antenna. Maybe your power rail is cleaner tha=
n
> 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 fr=
om
> >>>>> 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 that
> 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 cu=
t
> 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 the
> >>>>> 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 suppl=
y
> >>> when
> >>>>> the
> >>>>>> relay is turned off.
> >>>>>>
> >>>>>> Is the transistor being turned on hard enough to keep the relay on
> >>>>> 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.jpg
> >>>>>>>
> >>>>>>> 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 conduct=
ed
> >>>>>> 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.jpg
> >>>>>>>
> >>>>>>> I was over at someone else's place so did not have a lot of parts
> with
> >>>>> me,
> >>>>>>> but...
> >>>>>>> Adding a bunch more 0.1uf bypass capacitors all over the board di=
d
> not
> >>>>>> help.
> >>>>>>> Changing the power supply from an IRM-10-5 (industrial spec, 200m=
V
> >>>>>>> ripple) to MPM-10-5 (medical spec, 100mV ripple), helped reduce t=
he
> >>> rate
> >>>>>> of
> >>>>>>> the crashing... but the ripple itself wasn't causing crashing.
> >>>>>>>
> >>>>>>> Adding (non-specific size) ferrites to the pump wires, and 120VAC
> >>> 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.jpg
> >>>>>>> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-03.jpg
> >>>>>>>
> >>>>>>> FWIW, this is where it ended up...
> >>>>>>> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-04.jpg
> >>>>>>>
> >>>>>>> The noise is in the 7Mhz to 30Mhz range (prob even higher).
> >>>>>>> I feel like smaller, low-ESR ceramic caps should help, but I doub=
t
> 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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