CD Changer emulator to fool CD player

Hi everybody!
As title says, I want to fool my car cd player that cd changer is present. My car player is BLAUPUNKT 937 with next pinouts:



Blaupunkt 937 is using DMS protocol to comunicate with CD changer

Blaupunkt DMS

I want to connect 3,5mm audio jack to pins 18,19,20 to get some kind of AUX, but I need to fool cd player... HELP!

is this what you mean?

To summerize -- You're car audio system has two parts, a cd changer and the actual audio player. The cd changer swaps discs, plays the discs, and sends the analog audio to the audio player through it's aux ports. And, based on the links you gave, the two devices communicate via a serial protocol. You want to ditch the cd charger and plug in your own device to play music, like an mp3 player.

But, the problem is that when you disconnect the cd changer the system stops working because it thinks that the cd changer is gone. I suppose you want to build a device that will travel in your car that will make this happen.

I see this project having three large parts.
part 1: Making a cable that will connect to the audio player (audio player to serial port)
part 2: Using the serial port on a PC to figure out the right sequence of commands to send to the audio player
part 3: Making some portable solution. So, taking a processor and programming it to automatically do what you did in part 2

I imagine that there are going to be some pitfalls in there, but I can't predict what they are going to be.

Do you have any more specific questions?


p.s.
Reading about this somewhere, I saw that depending on the firmware version of your player there is another solution which allows you to short a couple of pins together to make this happen. I don't know what those pins are, but according to what I read, it is a hit and miss solution.

Re: is this what you mean?

Yes, there is a possibility to short connect pins 13 & 14 and you will get cd changer mod. But, problem is when you want to switch between FM radio, internal cd player and cd charger... if you put this "aux" cable you can use car player only in cd changer mode... nothing will happen if you press "source" button on device to switch FM or internal cd... connecting pins 13 & 14 shortly, player is always in cd changer mode until you dont disconnect pins 13 & 14...

I have analog audio signal from my 3,5 mm audio jack from external mp3 player which i'm going to DIRECTLY connect to pins 18,19,20 and that will work only if I put car stereo into cd changer mode... so I have to fool him.
I'm new to programming MCU, so... help please

What microprocessor have you chosen to use? Does it come with a pre-built development board? Would you like help choosing one?

You will have to setup the microprocessor for serial communication. Specific instructions should exist for doing that no matter what processor you choose (as long as it can). I would expect the devices that manages serial communication on your processor to be called a UART. I don't have much experiance with that, but I'm sure lots of people here would be able to answer specific questions on that point.

You can make sure that your serial connection is working okay by connecting the device to the serial port on your PC (assumming you have one). If you are using windows, you can use hyper terminal to send characters directly to the microprocessor (or whatever is plugged in). That way you can be sure that you have the processor setup correctly before you plug it into your radio and expect it to work (it won't because nothing works the first time). Doing that step will give you a foundation for trying to debug the link between the processor and the radio.