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Ground Loop Isolation with Raspberry Pi
#1
Hello All, I have a Raspberry Pi 4 B wired into a 12v to 5v 3A DC to DC connector, this connector is wired directly into the same wiring harness that the amp is. My amp that I have is wired directly to the wring harness that leads to 12v battery ground. 

With the raspberry pi disconnected from the amp and the 3.5mm connected to my phone, the ground loop whine is gone, but when it is, I notice the classic signs, alternator whine, and changing with engine RPM's. I've tried wiring it to the 12v cigarette adapter with no luck, I've tried grounding both the amp and the Pi in the same spot on a chassis grounding bolt with no luck. 

I did notice however that when using the GIPO ground pin in the number 9 slot, it reduced the whine a tad when grounded.

Is there something I'm missing? I don't understand where there could be a ground potential difference and as to why the Pi isn't fully cooperating. Any advice is welcome!

P.S. if someone could tell me whether or not the Pi can accept SWC controls over its 3.5mm jack and how to decode them, that would be fantastic as the SWC module I have has a 3.5mm output.
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#2
You answered to your own question in the title of your thread.
All you need is "ground loop isolator" between sound card and ampiflier.
Raspberry Pi 4b-4gb / Official 7" touchscreen / OAP 5.0 / Honor 8x (AndroidAuto 5.) / USB sound card / USB microphone
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#3
(07-06-2020, 05:48 AM)skrimo Wrote: You answered to your own question in the title of your thread.
All you need is "ground loop isolator" between sound card and ampiflier.
I understand that a ground loop isolator will help, but it's only a temporary solution as it minimizes the signal. I was wanting to fix the solution. I have one on order in the meantime, thank you for the advice.
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#4
Oh didnt know that GLI only minimizes the signal. I always thought that that's the only solution.
Raspberry Pi 4b-4gb / Official 7" touchscreen / OAP 5.0 / Honor 8x (AndroidAuto 5.) / USB sound card / USB microphone
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#5
I'll agree that a Ground Loop Isolator is not the best solution, and in some cases do nothing to get rid of the noise, and mostly attenuate the audio signal.

YouTuber GreatScott has a video on this.

https://www.youtube.com/watch?v=n_b_0BWP0mI

I've been meaning to get a few of those B0505S-1W DC to DC isolators and give them a try. They are pretty cheap. You just have to remember that they are only good for 200mA, they do not do any voltage regulation, and they do require a minimum current on their output. You might have to add a small load resistor if your sound card does not draw enough current. Obviously only having 200mA of output shows that you can't use one on the amplifier itself, just the sound card.
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#6
(07-06-2020, 03:22 PM)jhornbr225 Wrote: I'll agree that a Ground Loop Isolator is not the best solution, and in some cases do nothing to get rid of the noise, and mostly attenuate the audio signal.

YouTuber GreatScott has a video on this.

https://www.youtube.com/watch?v=n_b_0BWP0mI

I've been meaning to get a few of those B0505S-1W DC to DC isolators and give them a try. They are pretty cheap. You just have to remember that they are only good for 200mA, they do not do any voltage regulation, and they do require a minimum current on their output. You might have to add a small load resistor if your sound card does not draw enough current. Obviously only having 200mA of output shows that you can't use one on the amplifier itself, just the sound card.

I also found that using existing wiring for power was the biggest factor to the interference sound.  I fixed this by running a new circuit from the fuse block using 14ga wire to provide power to my 12v to 5v converter.  I also use the GLI too.
Thanks, Frank
Carputer Detail   Parts List
2004 Chevrolet Tahoe Z71 w/ Bose & Onstar
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#7
(07-29-2020, 05:32 PM)frankpintosr Wrote:
(07-06-2020, 03:22 PM)jhornbr225 Wrote: I'll agree that a Ground Loop Isolator is not the best solution, and in some cases do nothing to get rid of the noise, and mostly attenuate the audio signal.

YouTuber GreatScott has a video on this.

https://www.youtube.com/watch?v=n_b_0BWP0mI

I've been meaning to get a few of those B0505S-1W DC to DC isolators and give them a try. They are pretty cheap. You just have to remember that they are only good for 200mA, they do not do any voltage regulation, and they do require a minimum current on their output. You might have to add a small load resistor if your sound card does not draw enough current. Obviously only having 200mA of output shows that you can't use one on the amplifier itself, just the sound card.

I also found that using existing wiring for power was the biggest factor to the interference sound.  I fixed this by running a new circuit from the fuse block using 14ga wire to provide power to my 12v to 5v converter.  I also use the GLI too.


So if i get it right the ticker the wire to the 12v to 5v converter the better and the less interference you get?
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#8
Photo 
Thicker wire within reason. Mostly just to get away from using the cars wiring. Auto manufacturers use the smallest possible gauge wire for the anticipated load. That saves money on wire and weight. NFPA 70 says that 14AWG wire is good for 21 Amps. We're not using anywhere near that. Noise Isolation is a science all to itself.

I have designed a circuit board at JLCPCB, and received them last week. Components also arrived last week. I need to get to soldering and try this thing out.

Pics are attached. It's got Opto-isolated inputs for illumination, ignition, reverse. It's got a little section for one of those Isolators powering a USB port. It's got a couple relays to power not only the external timer circuit, but also my screen when you put the car in reverse. It's got a spot for an RTC to sit, and screw terminals for an external temp sensor. Also a little prototyping area, in case I want to add some features later.

   

   
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#9
For powering/switching the radio on and off I use a switch at the moment. I got an old VW Golf 2 so it hasn't have any remote antenna wire mostly blue) so its wired to my key 12v to power on my external AMPS..
Suppose this wouldn't be an issue?
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