From: Jason White <whitewaterssoftwareinfo@gmail.com>
To: Microcontroller discussion list - Public. <piclist@mit.edu>
Sender: "piclist-bounces@mit.edu" <piclist-bounces@mit.edu>
Date: Sun, 13 Dec 2020 15:58:19 -0800
Subject: Re: [EE] Eliminating external noise through PS
Thread-Topic: [EE] Eliminating external noise through PS
Thread-Index: AdbRrVDCyob9rERdTpmq2aL05Bc5Ug==
Message-ID:
 <CAOFvGD40+Nk9Ei_L1GmUp9DPWaOpFDD1940EFG4gy21ovaKk=Q@mail.gmail.com>
References: <5FCFC00E.8040703@narwani.org>
	<004f01d6cf54$9da13a80$d8e3af80$@functech.com>
	<5FD3D1E9.8040605@narwani.org>
	<CAOFvGD6p9ft6iymUzaeSP99jmLVOHxXQbBHLHyP6FDck+n7TvA@mail.gmail.com>
	<5FD6A0DC.4010801@narwani.org>
In-Reply-To: <5FD6A0DC.4010801@narwani.org>
Reply-To: Microcontroller discussion list - Public. <piclist@mit.edu>
Accept-Language: en-US
X-MS-Exchange-Organization-SenderIdResult: TempError
X-MS-Exchange-Organization-PRD: mit.edu
X-MS-TNEF-Correlator:
received-spf: Pass (protection.outlook.com: domain of gmail.com designates
	209.85.208.51 as permitted sender) receiver=protection.outlook.com;
	client-ip=209.85.208.51; helo=mail-ed1-f51.google.com;
dkim-signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com;
 s=20161025;
	h=mime-version:in-reply-to:references:from:date:message-id:subject:to;
 	bh=QglFo+qk8mVA1jjfVYOTjoAIOHREu0+Blnx07/0vVEI=;
	b=jlnXaxjUzaCD5epYx59Hu6vPLYLUD1cmP7hYuTccawuxqeumpfLAgDpYkNYFPnRGoO
	vizwuglzHPGuqH8ZnEzJbY9DyQlQQTpWp64LIKopfYUpOZL3bke6C+yQNf/+h8VIolAh
	6Yu/ZzTO0m6bkhmpSs7dgyixvdcA0GskwgGCkucOmW2FbpamQKs/SIhrp5P/1M7NT4zQ
	uC/M/uFF196eyB76dGrfBVdJQzT+dxdzzxDPIhL5S2gMUwYPJAS/jbRozwExWaH1EU7n
	DuxUTndQDTnpZ13llPKzxd7WQbvzaYnb2XPRscLcyAXHwXyIGuyn9T7U8vXnfwCBYiqX	3f+w==
authentication-results: spf=pass (sender IP is 209.85.208.51)
	smtp.mailfrom=gmail.com; mit.edu; dkim=pass (signature was verified)
	header.d=gmail.com; mit.edu;	dmarc=pass action=none header.from=gmail.com; 
errors-to: piclist-bounces@mit.edu
list-id: "Microcontroller discussion list - Public." <piclist.mit.edu>
list-post: <mailto:piclist@mit.edu>
x-beenthere: piclist@mit.edu
x-mailman-version: 2.1.6
x-received: by 2002:aa7:da07:: with SMTP id
 r7mr22253920eds.309.1607903900729; 	Sun, 13 Dec 2020 15:58:20 -0800 (PST)
x-topics: [EE]
x-content-filtered-by: Mailman/MimeDel 2.1.6
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: quoted-printable
MIME-Version: 1.0

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), 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 120VAC
> 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 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 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 y=
ou
> > 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 abo=
ve
> >> 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 shoul=
d
> >> run two 3.3V regulators instead?  I would think that the buck converte=
r
> >> 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. Di=
d
> >> 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, b=
ut
> >> there's a bridge rectifier on the wires.  So I'm now convinced that th=
e
> >> 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 a=
nd
> >> 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 flyba=
ck
> >>> 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 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 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 happe=
ns
> >> to
> >>>> generate a LOT of conducted noise, which passes through the 5V PS, a=
nd
> >> 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 parts wi=
th
> >> me,
> >>>> but...
> >>>> Adding a bunch more 0.1uf bypass capacitors all over the board did n=
ot
> >>> 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 120VAC
> input
> >>> wires
> >>>> did not help.
> >>>> I then tried to create a crude/uncalculated LC filter (which whateve=
r
> >>>> components I had on hand (33uh inductor and 1000uf capacitor, should
> be
> >>>> low ESR), then a Pi filter (added 680 uF capacitor), and those barel=
y
> >> 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 doubt i=
t
> >> will
> >>> take
> >>>> out most of the noise.
> >>>> What is the right type of filter to eliminate this noise?
> >>>>
> >>>> Cheers,
> >>>> -Neil.
> >>>>
> >>>> --
> >>>> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> >>>> View/change your membership options at
> >>>> http://mailman.mit.edu/mailman/listinfo/piclist
> >> --
> >> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> >> View/change your membership options at
> >> http://mailman.mit.edu/mailman/listinfo/piclist
> >>
> >
>
> --
> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist
>


--=20
Jason White
--=20
http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
.