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Ground Looping Isolation

Forum 1
(@osman)
Eminent Member

@milad

Hey Milad,

I have the following problem. I want to avoid ground looping in UART communication. Can I isolate this by this part Digital_Isolator ?

If so, is my schematic (See attached) correct?

Kind Regards

Osman

Quote
Topic starter Posted : 20/09/2021 4:08 pm
SOLO Team
(@milad)
Chief Member Moderator

Hi @osman,

The wiring diagram you proposed is, unfortunately, unable to insulate the signals of the UART for the following reasons:

- any signal insulation not only needs a way to insulate the signal itself ( like the IC you used) but it also needs the insulation of the supplies, the power supply you used ( 24V to 5V converter) is a Buck converter which doesn't offer any insulation.

So to solve your problem you need to add an insulated DC-DC converter like this one into your circuit in a way that, this insulated supply will convert the non-isulated 5V from the BUCK to the insulated 5V for the secondary side of the signal insulator you used.

https://www.mouser.it/ProductDetail/CUI-Inc/PYBJ3-D5-S5-OD?qs=W%2FMpXkg%252BdQ4lQxIgaM0bkA%3D%3D

Forum 3

so in practice based on your initial wiring, and the image above for the schematics of the DC-DC mentioned, you need to :

  1. Connect the +5V or your BUCK to Vin of DC-DC
  2. Connect the Negative terminal of your BUCK to GND of DC-DC
  3. Feed Arduino only with the Vo and 0V of the DC-DC ( Arduino must be completely on the other side of the insulation and no signal should go to the other side without passing through an insulation barrier including GPIO's and etc)
  4. connect the VDD1 on your Insulator IC to the +5V of the BUCK
  5. connect the GND1 on your insulator IC to the Negative terminal of the BUCK
  6. connect the VDD2 on your Insulator IC to the +Vo of the DC-DC
  7. connect the GND2 on your insulator IC to the 0V of the DC-DC
  8. The rest can remain like now in your wiring

So it's clear that we fully put Arduino on 1 side of the isolation barrier and the rest of the circuit on the other side, and this can give you a way to avoid ground loops. You can share with me your refined wirings here to do the last checks.

I'll remain available.

Milad

 

If you found the answers helpful and you could solve your problems, please kindly verify here to help others in the future.

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Posted : 21/09/2021 7:46 am
Forum 1
(@osman)
Eminent Member

Hey Milad,

Thank you very much for the very good explanation. Before I create a circuit diagram, I would like to ask you if "DC/DC Converter" can also use this DC/DC converter? Here you have the "datasheet" of it.

Kind regards
Osman

ReplyQuote
Topic starter Posted : 21/09/2021 7:56 pm
SOLO Team
(@milad)
Chief Member Moderator

Hi @osman, for your application this one is the same as the other, in general one of the main characteristics of the insulated DC-DC converters is their parasitic Input-output capacitance for very sensitive systems, but here in our case it's not that important especially for low power signals like UART.

So I believe you can use the DC-DC you offered here without any problem and same as the one I showed you in the first post with the same idea of wiring and connection, you can also share with me here the final wiring diagram to review together if you like.

Regards
Milad

 

If you found the answers helpful and you could solve your problems, please kindly verify here to help others in the future.

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Posted : 21/09/2021 8:00 pm
SOLO Team
(@milad)
Chief Member Moderator

Hi @osman,

I wanted to add a point to all said up to now:

- Make sure you don't connect SOLO and the Arduino to the same PC or laptop through USB, if you do that you are bypassing the isolation barrier again as the USBs of PCs are having shared grounding ( never seen a PC with insulated USB as the price would sky rocket), any connection through a medium must pass through an insulation barrier of somehow as mentioned.

There are USB insulators, but I believe if you only work with UART you can avoid using the USB, so during setup times if you use USB, make sure you connect only one of them to your PC.

Regards

Milad 

If you found the answers helpful and you could solve your problems, please kindly verify here to help others in the future.

ReplyQuote
Posted : 22/09/2021 1:22 pm
Forum 1
(@osman)
Eminent Member

@milad 

Hey Milad

Thank you for the advice, which is very much appreciated. I have created the following wiring diagram, does it look reasonably ok like this?
Kind regards
Osman

ReplyQuote
Topic starter Posted : 22/09/2021 6:50 pm
SOLO Team
(@milad)
Chief Member Moderator

Hi @osman

I see some issues as below :

  1.  The VDD1 of the insulator chip (purple board) should come from the BUCK converter ( the blue board) and not the DC-DC, like this, you are violating the isolation barrier since now there is one path from one side of the circuit to the other side without passing through a barrier.
  2.  GND2 should also get connected to the output 0v or return of the DC-DC ( you always need a reference to the real ground )
  3.  Connect the VDD2 directly to the output of the DC-DC and not the Arduino (let's use Arduino only for signalling and low power stuff)

 so pls modify the schematics as mentioned and we can check it again together here.

Milad

 

If you found the answers helpful and you could solve your problems, please kindly verify here to help others in the future.

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Posted : 23/09/2021 12:09 pm
SOLO Team
(@milad)
Chief Member Moderator

@osman

I forgot to say that, of course, you need to disconnect the VDD1 connection to VDD2, that's not allowed, and they must be connected independently each on  1 side of the DC-DC .

Regards
Milad

If you found the answers helpful and you could solve your problems, please kindly verify here to help others in the future.

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Posted : 23/09/2021 12:11 pm
Forum 1
(@osman)
Eminent Member

@milad 

Hey Milad

I have used a test version of a circuit diagram software. Unfortunately, you can see the advertising of the software company on the picture. I hope that this is not so important for our purpose.

I have created a new circuit diagram. Is it correct?

Kind regards
Osman

ReplyQuote
Topic starter Posted : 24/09/2021 8:06 pm
SOLO Team
(@milad)
Chief Member Moderator

Hi @osman,

Yes, the wiring is great and it seems like a solid and professional piece of isolation for your purpose.

In general, be thoughtful about any future connections that can bypass this barrier...

I will remain available.
Milad

If you found the answers helpful and you could solve your problems, please kindly verify here to help others in the future.

ReplyQuote
Posted : 24/09/2021 8:11 pm
Forum 1
(@osman)
Eminent Member

@milad 

Thank you, I'm glad to hear that.

ReplyQuote
Topic starter Posted : 24/09/2021 8:22 pm
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