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I connected a Raspberry Pi 2 in the car to add OSMC media player capabilities. However, there seems to be a buzz / hum of background noise in the audio. The noise is correlated to the engine speed so it seems to be coming from the Alternator.

What are some different method of fixing this?

Is there some kind of shielding that could be implemented?

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  • \$\begingroup\$ Usually the spark plugs, not the alternator. They are a far more effective noise source, what with a few kilovolts zapping away in a pulsed manner. But I guess yours was perhaps a crummy switcher in the USB power device. \$\endgroup\$ – Ecnerwal Dec 18 '15 at 15:34
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All old car radios had filter components on the incoming 12V rail. New stuff probably has some filtering as well. Car audio retailers sell inline filter chokes to quiet noisy installs. Some cars are noisier than others. Connecting straight to the battery via a fuse is generally regarded as the way to go for lowest noise. The reasoning being that the car battery forms a natural filter.

The old car stuff had an inductor in the low milli-herny ballpark and an electrolytic cap of around 1000 microfarads. These days you could try a cheap 500 micro-henry ferrite bobbin core inductor with a 2200 microfarads electro capacitor.

The reasoning for my value changes is that the old chokes were laminated iron and now expensive and the bobbin core ferrite coil can be had at only 500 micro-henry at small size and reasonably low DCR. The cap value increase roughly makes up for the inductance decrease. This stuff works on car radios so it should work for you.

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    \$\begingroup\$ Just remember to size the inductor appropriately - if the PI will consume 1A continuously max, the inductor likely needs to be rated for twice that or more to ensure it doesn't overheat and catch fire. Multiply it's DCR by the current going through it to get Watts of dissipation; the lower the better. Also consider that inside a car, the ambient temperature may reach 60°C or more. De-rate everything for the hottest ambient temperature it will ever be exposed to. \$\endgroup\$ – rdtsc Dec 18 '15 at 15:12
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There ended up being 2 issues to solve in fixing the background noise issue.

1) I bought a ground loop noise isolator. Put this in line with he RCA audio cable, with ground lead connected to the cars battery ground.

Here's the noise isolator I bought: http://www.amazon.com/gp/product/B000K50HJE

2) The 12v to USB power adapter / converter I was using initially was a really cheap one that wasn't providing good power to the Raspberry Pi. I replaced this with a much better one.

Never use cheap USB power adapters. Here's the USB power adapter I bought: http://www.amazon.com/gp/product/B00VH8VHWO

After making these 2 changes to the system, the audio no longer has any hum or background noise.

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  • \$\begingroup\$ The reviews of those noise isolators describe my problem exactly. But is there a way to solve this myself? I'm using a mod on a 2000 Pontiac Grand Prix where you tap into the in-dash CD Player digital audio wires and connect them to a Radio Shack mini jack, creating an AUX jack for your iPhone/iPod. I get the noise whenever the engine is running. Is there some type of grounding I need to change inside the CD player? When I wired the jack, I followed someone's guide online about running a ground to the CD player to eliminate noise. I wonder if I'd be better off removing that ground? \$\endgroup\$ – Syclone0044 Jan 31 '16 at 23:53

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