Author Topic: Avoiding newbie mistakes that causes noise  (Read 608 times)

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Offline mendez

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Avoiding newbie mistakes that causes noise
« on: October 08, 2019, 04:26:37 pm »
Hello,

I'm not an electrical engineer, so please go easy on me.

I need to make sure I "avoid" newbie noises in my Hardware. I understand that the arduino might be noise; but I just want to make sure I understand the general rule for properly grounding.


1. My understanding is that is "recommended" to use shield cable if I want to connect an external Sensor and a Micro-controller. But what about the shield wire (or extra GND i call it):

- Do I connect the shield metal wire (SGND) to the GND of the microcontroller? In this case, the Arduino Gnd?

- I have seen PCBS that have a GND and SGND; How do I do make a SGND in the actual PCB?

- If I use the diagram attached (simple temp sensor); where do you connect the SGND from the shield cable if I have a shield cable connected to the sensor?


2. Should I enclose the PCB using Faraday Cage method? Ex. can I enclose the Arduino and this will help avoiding noises?

3. If I'm using sensitive sensors; should I try to avoid using a Laptop? and instead use a PC?


I guess; i need basic tips that can make a big difference when starting to design a PCB from the beginning. Thanks for the help!
 

Offline lawrence11

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Re: Avoiding newbie mistakes that causes noise
« Reply #1 on: October 08, 2019, 05:58:09 pm »
We were all noobies once, and we grew bigger by reading a few pdfs. Coming here to learn about basics is just wasting peoples time.

Its your responsibility to read about proper techniques in the many PDF's that are available online.

TI comes to mind, I studied their documents alot.

But it can be summed up like this, keep ground loop as small/close  as possibl, so a ground plane beneat a trace, and a ground via besides a via.

" when The positive electricity searches far away for its negative side, the field is big, and so is the radio emissions"
 

Offline rstofer

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Re: Avoiding newbie mistakes that causes noise
« Reply #2 on: October 08, 2019, 08:31:54 pm »
Yes, you connect the shield to ground, preferably on the uC end.  I would not ground it in two places.  Truth be told, the Arduino has no Earth ground reference so it wouldn't matter if you grounded both ends but what you don't want is the potential difference between two Earth points flowing through the shield.

This is also the way they play the shield game in audio systems.  Grounded on one end only and usually the driving end.

 

Offline fchk

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Re: Avoiding newbie mistakes that causes noise
« Reply #3 on: October 09, 2019, 11:16:00 am »
1. Be only as fast as you need to be. There are often chips with different speeds (eg. logic gates, RS232/422/485/CAN transceivers,...) Versions with lower speeds are better optimized for EMV, they emit less noise.

2. The area of a current loop should be minimal. Current should go the same way from the source to the sink and from the sind back to the source. Otherwise you create a loop with one winding, and all manitic fields fluctuating inside this loop with induce a current.

3. Use solid ground planes (same reason as #2)

4. Connection to the outside world (PC,...): Use digital isolators or optocouplers to avoid ground loops.

5. Shielding of cases or wires: You want charges to flow to ground, but yyou don't want current flowing from one side of the shield to the other in a cable. So put a resistor (100k) or capacitor (100n) between frame ground and system ground.
 

Offline MarkF

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Re: Avoiding newbie mistakes that causes noise
« Reply #4 on: October 10, 2019, 12:55:10 pm »
To start-
Avoid release of the magic smoke!

(If that is a NPN transistor (2N3904), it is shown rotated 180o)

« Last Edit: October 10, 2019, 01:12:38 pm by MarkF »
 

Offline jackthomson41

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Re: Avoiding newbie mistakes that causes noise
« Reply #5 on: October 10, 2019, 03:36:31 pm »
No need of being so conscious about soldering, simply use breadboard and connect the pins of 2N3906 test it out, even if you make the wrong connections, that's how you will learn.
« Last Edit: November 17, 2019, 10:47:46 am by jackthomson41 »
 

Offline TomS_

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Re: Avoiding newbie mistakes that causes noise
« Reply #6 on: October 13, 2019, 08:56:00 am »
Coming here to learn about basics is just wasting peoples time.

Dont try and dictate what other people may or may not be able to offer.

If its not worth your time, ignore it and move on. Its a very simple concept.

Or perhaps flag it to the mods and ask them to move it to the Beginners forum?

 
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