From: David VanHorn <microbrix@gmail.com>
To: Microcontroller discussion list - Public. <piclist@mit.edu>
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Date: Wed, 30 Dec 2020 22:07:22 -0800
Subject: Re: [EE] Eliminating external noise through PS
Thread-Topic: [EE] Eliminating external noise through PS
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10k might be light.  Try 1k pullup, and 100nF to ground?

On Wed, Dec 30, 2020 at 5:26 PM Neil <picdude3@narwani.org> wrote:

> Interesting thought... 10k pullup to +3v3.
>
>
>
>
> On 12/29/2020 5:13 PM, David VanHorn wrote:
> > 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 use=
d
> >> 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 , an=
d
> >> noise is mostly in the few Mhz range and higher.
> >>
> >> - Ceramic cap across (DC) motor wires (right at the motor) helped a bi=
t.
> >> - 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 ru=
n
> >> the pump, and a 1k load resistor on the PS output. Still a lot of nois=
e
> >> - 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 t=
o
> >>> 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. Ha=
ve
> >> 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 separa=
te
> >>>> 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),
> and
> >>>>> it was (expectedly) very clean (on the scope).
> >>>>> (b) disconnected both of the pump wires and plugged it into the
> female
> >>>>> side of a PC power cord, so the pump ran, but was connected to 120V=
AC
> >>>>> from a different source.  Very clean power again.
> >>>>> In both cases, all else stayed the same including where the wires
> were
> >>>>> draped, etc.
> >>>>>
> >>>>> In other tests, I moved the scope, power lines, etc and no change t=
o
> >> 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
> voltage
> >>>>>> 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
> scope
> >>>>> 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,  jus=
t
> >> 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 to=
p
> >>>>>>> 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, s=
o
> 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 fin=
d.
> >> 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 th=
at
> >> the
> >>>>>>> noise is coming from brushes.
> >>>>>>> I brought the pump with me, and I have a new blank board.  My pla=
n
> >> 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 t=
he
> >>>>>>> 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 i=
s
> >>>>> turned
> >>>>>>>> off. The lack of diode would cause a serious spike in the 5V
> supply
> >>>>> 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 wit=
h
> 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
> 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.jpg
> >>>>>>>>>
> >>>>>>>>> I was over at someone else's place so did not have a lot of par=
ts
> >> 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,
> 200mV
> >>>>>>>>> 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 120V=
AC
> >>>>> 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 o=
f
> >> 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
> 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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