[EE] Eliminating external noise through PS

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Re: [EE] Eliminating external noise through PS

Soooo.... yep, this was actually the reason for the last bit of noise I
was seeing... the probe.  Tried the paperclip ground again and it's 99%
Really appreciate everyone's help on this!
I'll go back and calculate ideal values for the filters etc now.

Happy New Year everyone!


On 12/30/2020 7:04 PM, Neil wrote:

> I had previously tried the paperclip-ground mod for the scope probe
> (saw this from one of Alan Wolke's videos a long time ago) and it
> didn't make much difference.  I should really try this now, after all
> the changes.
> Cheers,
> -Neil.
> On 12/29/2020 2:36 PM, Jason White wrote:
>> My experience developing "all discrete" (no microcontroller) motor
>> driver
>> PCBs is that any noise that is unaffected by filtering tends to be a
>> measurement or environmental artifact.
>> I'd recommend doubled checking your probe/scope grounding - it is an
>> endless source of trouble and erroneous readings. I've found that often
>> times problems in systems are a result of a combination of "innocent
>> looking" and unrelated things that end up interacting in unexpected
>> ways.
>> On Tuesday, December 29, 2020, Neil <[hidden email]> 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 <[hidden email]> 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
>>> you
>>>>>>> think - in which case the true problem might be elsewhere.
>>>>>>> -Jason White
>>>>>>> On Fri, Dec 11, 2020 at 3:11 PM Neil <[hidden email]> 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
>>>>>>>> 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 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
>>>>>>>> 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
>>>>>>>>> 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: [hidden email] <[hidden email]> On
>>>>>>>>>> Behalf
>>> Of
>>>>>>>> Neil
>>>>>>>>>> Sent: December 8, 2020 11:04 AM
>>>>>>>>>> To: Microcontroller discussion list - Public. <[hidden email]>
>>>>>>>>>> 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
>>>>>>>>>> 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
>>> 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
>>>>>>>>>> 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
>>>>>>>>>> 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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