Powering in-car electronics

[Chris Edwards]

Hi all,

I've a project underway building a "carputer" and wanted some advice on
powering things. There will be a single-board ARM system (probably an
ODROID-C2) and touchscreen, some audio power amplifiers and an I2S DAC,
GPS receiver, FM radio receiver, and an array of I2C sensors (and maybe
a HUD).

I figure the main power supplies will be:
* 12 V 100 W worst-case for the audio amplifiers.
* 5 V 3 A for the computer and accessories.
* A low-noise 3.3 V supply with modest output current for the GPS and
FM receivers and the I2S DAC.

For the 5 V supply, a DC-DC converter seems the obvious choice (I'm
liking the look of some of the Murata modules).

For the 3.3 V supply, I was originally thinking of a linear regulator
powered from the 5 V supply, but I've read mixed opinions on whether
linear or switchmode will give lower noise. I know that for analog
audio, adjustable linear regulators are sometimes preferred for this reason.

The audio amps will tolerate 14 V (possibly 15), but I have reservations
about running them directly from the car's 12 V circuit
(battery/accessory) because of the voltage spikes and other nastiness
(the car has a spark-ignition engine).

The DAC feeding the power amps has a dedicated analog ground on the
output, so I wonder if an isolated DC-DC supply with suitable TVSS etc.
on the input might be a good way to go.

If I get a 12 V regulated supply, should I chain the 5 V converter off
that, or off the car's 12 V supply? What fusing or other protection
should I use?

This is a one-off build so no PCB planned - just an assembly of modules
from the likes of Adafruit. :)

Thanks for any suggestions!
Chris

[Ian Rees]

Hey Chris!

    Yeah, I'd just hang the 5 and 3.3V each off of whatever you end up sorting out for the 12V.  The car stereo can probably be hooked up straight to your car's electrical system, you'll just want to put some filtering on it (I think folks typically stick a big cap near their load, a series choke probably isn't a bad idea before that) and be real sure the stereo isn't going to drain the car battery when you're not driving it (series relay with the coil powered by the car accessory).  One of the bigger issues with car electrics is grounding - probably best to run two conductors between your car battery and the amp.  Tons of folks are in to car stereos  - I'm sure there are resources online.   -Ian-