Questions tagged [emc]

Electromagnetic compatibility (EMC) is a branch of electronics related to identifying and solving problems caused by electromagnetic interference (EMI) between devices. It encompasses both attempting to prevent unwanted emissions from a device and also ensuring that emissions from another device will not cause spurious operation. EMC depends upon many system-level details; when asking questions, please provide as much information as possible.

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What does the Y capacitor in a SMPS do?

It seems that a well-designed SMPS has a capacitor connecting the ground planes of the primary and secondary sides of the transformer, such as the C13 capacitor here. What is the purpose of this ...
Dolda2000's user avatar
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43 votes
3 answers
5k views

What's radiating on my PCB?

I recently did a proper EMC test on a PCB of mine. It failed the test, and seems to be radiating in the 300MHz - 1GHz region, with peaks every 50MHz, and little peaks on the 25MHz. Looking at the ...
Rocketmagnet's user avatar
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38 votes
4 answers
2k views

Identifying Source of Periodic Artifact at Op-Amp Output

My MAX44251 dual op-amp has a very small unwanted 131KHz periodic artifact at the output, seemingly regardless of how it's configured. My assumption was EMI, but I can't see this 131KHz signal on any ...
Keegan Jay's user avatar
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33 votes
2 answers
5k views

Ground ring -- good or bad?

Here are two routings: Which is better? On one hand, the first is bad because ground ring is one-turn coil, hence induction current will be appear. On other hand, the second is bad because potential ...
user avatar
29 votes
5 answers
6k views

Why do some EMI/RF shields have holes on the top and some don't?

I am not talking about cutouts for tall components. I don't think they are for ventilation as they are often covered with manufacturer labels.
Dojo's user avatar
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29 votes
4 answers
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Why is it good to slow down digital lines with resistors?

I've heard that sometimes it is recommended to "slow down" a digital line by putting a resistor on it, let's say a 100 ohm resistor between the output of one chip and the input of another chip (...
Alex I's user avatar
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24 votes
2 answers
12k views

Via fences for noise reduction of a chip antenna?

I'm working on a 4-layer PCB that has a wifi module and a chip antenna, the antenna is placed at the corner of the PCB and the copper beneath it is removed, I see that via fences are used on the ...
mux's user avatar
  • 1,866
24 votes
2 answers
5k views

Alternatives to SPI because of EMI

I currently make a system consisting of a plastic enclosure which contains an MCU talking to 7 ADCs using 2MHz SPI over wires about 5cm long. The problem is that I'm concerned about EMI. Everything ...
Rocketmagnet's user avatar
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23 votes
3 answers
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Is twisting a single ended signal with its own GND really useful?

I know that the most robust way of transferring an analog signal over long distances is via differential pairs which are twisted together and then shielded (shield grounded at one end only). But ...
user42875's user avatar
19 votes
2 answers
5k views

PCB routing: EMI and signal integrity, return current questions

If there's any EMI/SI lesson I've taken in, it's to minimize return loops as much as possible. You can work lots of EMI/SI guidelines from that one simple statement. However, not having or ever even ...
darron's user avatar
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18 votes
3 answers
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What problems could occur when chaining 40 shift registers?

I'm planning on chaining together 40 x 74HC595 shift registers. The whole chain of 74HC595s will be controlled by a 5 V microcontroller, which will generate the SDI,...
m.Alin's user avatar
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17 votes
5 answers
8k views

Why does a simple conductor start to emit EM waves when carrying a signal?

I understand that on circuit board traces with a clock, if the higher harmonics have sufficient power, it results in electromagnetic waves being emitted from the traces which creates EMI. What I don't ...
quantum231's user avatar
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17 votes
3 answers
6k views

Why do some PCBs have exposed plated perimeters?

I've seen a number of PCBs, largely high speed and RF boards, that have exposed copper, either at the perimeter of the entire board, or in various sections, often with stitching vias. I've never ...
Kirill Safin's user avatar
17 votes
6 answers
2k views

Failed radiated emissions test on USB cable - USB module hardware and firmware improvements

I posted a few days about ago how our product failed ESD testing. Well, it also failed radiated emissions testing so I thought I'd make a separate post. The product is a 5V USB powered, non-radio, 3v3 ...
Geo's user avatar
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17 votes
2 answers
9k views

To "ground fill"or not to "ground fill"?

I have been reading up on the EMI issues in Electromagnetic Compatibility Engineering by Henry Ott. (wonderful book btw). One of the topics "PCB Layout and Stackup" (aka Ch 16) there is section about ...
Wally4u's user avatar
  • 323
16 votes
2 answers
3k views

Why are caps configured this way in EMC filters?

Every EMC filter I've seen has capacitors between the AC lines and earth, configured like this: simulate this circuit – Schematic created using CircuitLab Why are the caps not configured like ...
Stephen Collings's user avatar
15 votes
1 answer
16k views

PCB Ground and Power Planes

I am desigining a 4-layer PCB with the following stack-up: Signal Top, Ground Plane, Power Plane, Signal Bottom. This is the first PCB I make like this, which includes a noisy SMPS with a switching ...
Reuven's user avatar
  • 173
13 votes
2 answers
1k views

Best way to group power pins on a connector?

I am designing a little mezzanine PCB that uses Hirose DF12 connectors to connect to the motherboard. Four different voltages are delivered to this PCB: ±10v, 3.3v, 48v (and ground). They go through ...
Rocketmagnet's user avatar
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13 votes
1 answer
8k views

How to shield microcontroller from electromagnetic interference

I'm working with high voltage circuit (2.1 kV for defibrillator capacitor testing) and I'm controlling power supply with arduino, reading required information from laptop using serial interface. Most ...
user6266's user avatar
  • 135
13 votes
3 answers
2k views

The Pin 1 Problem in Audio, Star and Mesh Ground, and Contradictory Grouding Practices in Audio and Digital Systems

I recently came across the concept of "Pin 1 Problem" known in the pro-audio electronics. It seems straightforward at first, but becomes confusing when it comes to grounding. Let me describe ...
比尔盖子's user avatar
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12 votes
2 answers
1k views

Why do oscilloscopes use SMPSes instead of linear power supplies?

I'm wondering why digital oscilloscopes are using switching power supplies instead of linear power supplies. The SMPS has a higher efficiency, but it can produce some noise during high frequency ...
M.A.K's user avatar
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12 votes
4 answers
2k views

Why exactly is it discouraged to gap the ground plane?

From time to time I hear (and read) that it is not good to make separate Gnd planes for digital and analog circuit parts. It's all summarized in this rule of thumb: "Don't split the Gnd plane, don't ...
K.Mulier's user avatar
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12 votes
3 answers
8k views

Is it better to have a poor top layer copper pour or no copper at all?

For a few small 2 layers boards I'm doing, I'm using the top layer for parts and signals and a ground pour on the bottom layer with no or very short traces, based on comments and answers to my ...
mux's user avatar
  • 1,866
12 votes
2 answers
41k views

How does a ferrite core wire terminator work to reduce EMC?

The following question was asked on superuser: What is that cylinder on cables? How does that cylinder work? As far as I can tell, even if you put one on either end of the cable, any HF signal should ...
shieldfoss's user avatar
12 votes
5 answers
15k views

How can I improve USB EMI insensitivity?

I have several devices and some long cables on my PC's USB buses and every now and then I get a message like ...
jippie's user avatar
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12 votes
1 answer
4k views

How can electromagnetic interference from a USB charger cause a capacitive touchscreen to malfunction?

Electromagnetic interference from a USB charger can cause a touchscreen on a mobile device to malfunction, with symptoms such as reduced sensitivity or spurious touches. As an example, see http://...
bwDraco's user avatar
  • 1,381
12 votes
1 answer
5k views

PCB 'Emi proof' design

Currently I'm designing a GPS basestation which will have a radiomodem (broadcasting at 407-480MHz), a ARM7 microcontroller running at 60MHz and a FTDI USB chip. The FTDI USB chip even runs at 480MHz ...
Hans's user avatar
  • 7,208
11 votes
2 answers
3k views

What is this spongy material?

Hi, while I am tring to repair electronic circuit. I'm encountering this sponge. I wonder what is this sponge? and can I find out what it is used for. I often see this in sensitive circuits like in ...
mehmet's user avatar
  • 1,031
11 votes
10 answers
6k views

EMI: CFLs vs Incandescent Lights in Your Lab?

Being a green-oriented treehugger, I've put in all CFL lights in my house. Just as much light for about 1/4 or 1/3 the power. Nice, but flourescent lights put out a lot of EMI. Does this cause ...
11 votes
2 answers
886 views

how can power line 'orientation' influence electronic equipment?

Ok, long story short. I have a new TV that occasionally switches on all by itself. In case anyone is wondering it's a Sony XH90 and this problem is documented on www. Not trying to go into details ...
gommer's user avatar
  • 1,023
11 votes
1 answer
1k views

How close do I really have to place a 25MHz crystal?

I'm laying out a very space constrained PCB. Normally I would place a 25MHz crystal absolutely as close as possible to the chip using it. However, on this PCB, something else really needs the space ...
Rocketmagnet's user avatar
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11 votes
1 answer
3k views

What certification is needed for electronic devices in Europe?

I am going to be selling my project, Super OSD. It has a 3 MHz SMPS PSU and an 8 MHz crystal oscillator, but is not intended to emit radio signals. Will it be necessary to get testing to sell in ...
Thomas O's user avatar
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11 votes
1 answer
5k views

EMI/ESD protection for USB interface?

I'm a student making a simple Arduino-compatible board similar to the Pro Micro and am going to put a USB connector on the board. The schematic in the above link doesn't show any kind of EMI/ESD ...
Nate's user avatar
  • 4,476
11 votes
1 answer
2k views

Weak internal pullups on microcontrollers and EMI susceptibility

What disadvantages can I run into when using weak internal pullups (100k) on microcontrollers? I'm wondering how susceptible lines (with only parasitic trace/component capacitance) become to EMI ...
Steinar's user avatar
  • 768
11 votes
2 answers
1k views

EMI Issue: Ringing in switch mode power supply layout (5V -> 3V3)

I am working on a device which is undergoing testing to pass FCC part B (CSRR 22) emissions. At one angle and polarization (Vertical) the device fails as it has emissions in the 100-200Mhz range which ...
Kieran Duggan's user avatar
10 votes
2 answers
2k views

Hobby breadboard wiring guidelines to stay within legal RF/EMI limits?

Assume a middle school or home hobby lab with a bunch of breadboards, jumper wires, and 3.3V microcontrollers fast enough to toggle IO at RF frequencies (if not at the fundamental, at lower harmonics ...
hotpaw2's user avatar
  • 4,713
10 votes
3 answers
2k views

How does a bare PCB product such as a Raspberry Pi pass ESD testing for CE mark?

I am designing a product that is to be sold as a bare PCB as a finished product, and so requires EMC testing to be able to CE mark. I am new to designing for ESD, and protecting every single exposed ...
Matthew T Watson's user avatar
10 votes
1 answer
3k views

How serial resistors actually reduce EMI?

I am recently working with a GSM based system, and there was this advice in the datasheet of the GSM module: 22 Ω resistors should be connected in series between the module and the SIM card ...
Bence Kaulics's user avatar
10 votes
5 answers
2k views

What are some quick, cheap hacks for determining the source of EMI in my house?

TL;DR - Without dumping a bunch of money, is there a quick MacGuyver-y way to help diagnose what's causing the EMI in my house? Longer - I have the curse that I'm a little too technical to be helped ...
jdowdell's user avatar
  • 211
10 votes
2 answers
6k views

EMI Filtering on LVDS lines

This question is slightly related to: What's radiating on my PCB? These are Beckhoff's EtherCAT industrial IO modules. Each module is connected to its neighbours by 100mbps LVDS. Each module contains ...
Rocketmagnet's user avatar
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9 votes
7 answers
1k views

If mobile phones have to go through such extensive FCC/CE/EMI testing, why do they interfere with my radio?

It seems that to sell a GSM mobile phone, companies like Apple, Motorola, Sony Ericsson and many others invest a considerable amount of money in EMI testing them. Yet they still interfere with my ...
Thomas O's user avatar
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9 votes
3 answers
29k views

How important is the shield on an RJ45 connector?

If I am going to use a PCB mount RJ45 connector for 100mbps Ethernet, does it need to be a shielded connector, or can I get away with using an unshielded one? Is there some standard which deals with ...
Rocketmagnet's user avatar
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9 votes
2 answers
2k views

Does paint affect EMI ability of enclosure?

This could be a very stupid question, but when it comes to RF you never know. Does painting (non-conductive) over the top of a grounded metal enclosure affect its ability to absorb/block RF ...
Jack the Lad's user avatar
9 votes
1 answer
2k views

Spikes induced on PCB. EMC problem?

I designed the following PCB, where after testing a faced a severe (EMC related?) problem. This board houses an STM32F103 developing board. On the right of the PCB, there are 6 thermistors connected ...
Fotis Panagiotopoulos's user avatar
9 votes
1 answer
6k views

Capacitor and ferrite beads when to use which?

In this question Ferrite beads used to filter high frequency noise. Capacitor also can be used to reduced noise and filter out high frequency noise. Are they have the same effect on filtering high ...
pstan's user avatar
  • 901
9 votes
1 answer
3k views

common mode choke inductance question

In a common mode choke, my understanding is that common mode currents will produce fluxes that add together, which increases the effective inductance between them and so attenuating these currents. ...
EwokNightmares's user avatar
9 votes
3 answers
784 views

Is it safe to run long I/O wires to a microcontroller?

I'm contemplating using an MCU sitting in my garage to read data from a couple of sensors, one of which may be as much as 10m distant. I'm not using analog sensors, as this question asks, instead, I'...
Mark's user avatar
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9 votes
2 answers
3k views

4 layers PCB stack - (signal, signal, power, ground)

I've developed a board for a project and the company that is going to assemble it in a pluggable module has just asked me a weird modification. Currently it's a 4 layer board: top signal, ground, ...
FlyerDragon's user avatar
9 votes
2 answers
2k views

How to check whether a component can work in strong magnetic fields?

I want to design my PCB to operate nicely even when we place it next to a neodymium magnet. How to check whether my component can work in such condition without shielding? Edit: I haven't face any ...
pstan's user avatar
  • 901
9 votes
3 answers
612 views

Digital Signal Cables Penetrating a RF Shielded Room

Disclaimer: I'm not a trained electrical engineer...I'm a recent Computer Science grad with about ten years experience as a RF test tech. I don't know everything, and to me, experience reigns supreme ...
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