[SpookyZalost]

Greetings, Zalost here and today I'm going to start with a basic overview of an idea I've sorta had for a while, the concepts behind which allow anyone to modify both car stereo systems and potentially use them to make custom home stereo systems, for cheap and or out of recycled stuff potentially.

ok so you can approach this many ways but the big one is that you need a central unit that can do the following.

*Adjustable volume control.
*Adjustable channel levels (stereo quadrophonic, or more if you want 7.1 etc.)
*At least 1 external input.

ok so to start with in my example I'm going to use as my central unit, your standard car stereo with cassette player.
Why a cassette player? because the one's used in cars are slot loading and take up way less space, also as I found out through tinkering with various ones, easier to clean and maintain since they're less complex electronically.

in this case we'll use an alpine 7288, it as a port on the back for an external CD changer, more on this in a moment.



Notice the CD option on the 3rd button below the cassette bay.

see on the back there's a 7 pin DIN connector for plugging into a CD changer, but since it accepts standard Stereo audio input we can make use of it with a custom cable.



so once you have your stereo input the hard part is done, well outside of the power supply, but we'll get to that, it involves an old PC power supply

so once you have your AUX input (select CD on the main unit), what you need to do next is wire the stereo wires to a switch of some kind, I particularly like rotary switches for this but you can use any kind of switch you want, the number of poles is the audio channels you're switching plus ground and the positions/throws is the inputs so keep that in mind when you are selecting your switch/Switches.

in our case I'll be using this 3 position rotary.



basically what this does is let's you select the inputs on your device, you can also do a bus switch setup but that raises the complexity.

finally you'll need to select your inputs.

you've already got 2 thanks to that car radio, AM/FM and Cassette, you have 3 more for a total of 5.

in my example let's add a Bluetooth input 



Wire the channels as needed.

a CD player can be added using one of many projects involving a CDrom drive and an arduino or raspberry pi as the control and playback interface, many old CD rom drives also offered L/R channel audio out options reducing the complexity of this, just use the sbc as an atapi controller.

and finally your aux input, just wire up a standard headphone/aux jack to the front, unless you want to add dedicated RC plus in the back.

note: if you want to add both, use a bus switch (insanely cheap these), and wire the voltage line to the chip so that it switches if it detects signal, you can do this by wiring one of the inputs to both the bus and the VCC pins, I'd say do that for the front headphone jack input. (read 8mm TRRS jack)

you can obviously have fun and be creative with this, use multiple switches, use switches with more inputs, etc.

some of the inputs you can build/add include things like 8track players, Tracker file players (xm files, mod files etc.), MP3/digital audio players (read off SD card or flash drive, possibly combine with CD player?)

it's able to be whatever you want and that's the fun part.

finally you're going to need a computer power supply.

I recommend a modular one, that way you can make your own wiring harness for whatever devices you're rigging up and just plug it in after the fact.

the diagrams for the various pinouts are on the web, just remember that most of your car equipment uses 12volts so you'll need to account for this in your power supply.

luckily computer power supplies output 12 volts and are fairly regulated, just adjust the amperage using a variable resistor to make sure it outputs the correct amperage, most car stereos use around 5 amps so make sure to account for this when making your wiring harness between the power supply and radio unit, same with any other components.
here's the formula for figuring out what resistor you need.
(5-4)/0.36=R

do the same for all other devices, you'll find the majority are DC so just adjust as needed getting the starting voltage as close to the needed as possible, usually on the high side to step down and regulate it.

there's tons of information on the net regarding using resistors in DC circuits to output specific amps and volts so do more research on that unless you want to end up with the bad smelling "magic smoke" frequently talked about in electronics circles.

I'll answer any questions posted as they come up and post my own unit as I build it but I wanted to go over the theory and concepts first.