A solution for handyman
I was able to force the CD in of my radio with a different method :
I used a USB to I2C interface : http://www.robot-electronics.co.uk/htm/usb_i2c_tech.htm
- I opened my radiosat and soldered wires (I used telephonic wires cause it was the only small enought wire I had at this time) on the I2C bus by using the test point -> you need a very small tip on your soldering iron. You have 3 wires : SDA, SCL, Ground
- Those wires goes to the « USB to I2C » interface.
- I've done a small program in C that tell constantly to the TDA7342 to use the IN3 input (cause when the main processessor make a change, it won't tell to the I2C interface)
- The Audio left / right / ground are plugged on the CD connector at the back of the head unit.
And that's works ! (but it's not really user friendly)
There are many drawbacks :
- You need a computer.
- When the USB to I2C interface is not powered by the computer, the autoradio don't work (due to limitation of the I2C protocol -> I can give the details if someone is interested). You can solve it by putting a switch or a relay (powered from the USB 5V) between the interface and the I2C wires.
- When you change the volume / loudness / bass control / … there is a 1 to 2 secondes periode where the IN3 is lost and you hear back to the radio or tape unit. -> It's normal the head unit take the exclusive control of the input selector before the interface can take it back,
- Sometimes when you increase or decrease the volume, it go to max (quite surprising), -> I think messages from head unit and interface colide and produce this weird setting.
- The computer can't enter sleep mode while my program run (and if it try, you gonna struck your computer with the « going to sleep » screen). ->It's because my program don't take care of « go to sleep » message (I have to rewrite the code to handle it )
- If the head unit is on FM band when you force the IN3 input, the RDS / trafic advice / FM mode /… can produce « Bip » or small cut. -> the solution is to put the head unit on AM band.
- You can't use directly a sector powered device with the IN3 -> you need to use a galvanic isolator or an optic isolator on the I2C lines and on the audio lines (or you gonna crash the interface and heard a big blast from speakers)
I have not release it because my method is not user friendly; you have to put your radio to piece, weld wire, you need a computer, my software is unstable and not finished.
But if someone want's informations I can provide the C souce, the executable for windows (still in alpha but can work), and maybe pics (if can find them)
NB : It' been a while since my last english post -> sorry for mistakes
What happened to the project. Does development D2B-Interface?:Cry:
Hello to everyone,
Maybe this topic is already dead, but I am now playing with this unit and I can share some findings.
- As jedi83 wrote in previous post, TDA7342 is used for audio signal processing.
- Connecting AUX to IN3 (CD input) needs emulation of D2B communication to enable it.
This gave me simple idea, why wouldn't we use IN2 (tape input). Actually, who in these days use cassetes :).
- IN2 is enabled by inserting cassete into unit. That means, some kind of switch must be responsible for selecting IN2 input.
- I found simple mechanic switch probably responsible for this. It is present on PCB on tape module and is connected to 2 signal cables on ribbon cable which lead to main microchip 87cm21f.
If that switch is really responsible for selecting IN2, final solution is quite easy.
- Interrupt original IN2 tape input on TDA7342 and add AUX cable instead.
- Remove whole tape module (optional, but why to keep it inside)
- If 3.5 mm jack connector with inner switch is used, this switch can be connected to two signal cables on ribbon cable. When external device is connected with cable, jack switch is triggered and IN2 should be selected automatically. Alternatively, simple switch could be added to front panel of radio unit.
This solution is still NOT tested, as I have lot of other work to do. But if I am correct with above, you can have AUX input on your radio.
I am very happy about the progress in the subject. I hope to get a good result.