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.
Litle update after some time of inactivity. You can have AUX input on Radiosat 6010 and it works on mine. But I must warn you, you need good skills with soldering iron and knowledge of electronics. Don't ask for my advice, if you break something.
- The main object of interest is TDA7342. If you look into the datasheet (google for it), you will find, that it is some kind of two-ICs-in-one. The first part is responsible for selecting one of the inputs, based on data send from main microchip. Selected input is send to pin 3 (right channel) and pin 16 (left channel). And then immediately routed back via filtering capacitor to pin 2 and pin 15 to the second part of IC responsible for signal attenuation (volume, balance, treble, bass, etc.).
- There are special kind of 3.5 mm audio jack sockets with double switch DPDT. If you insert DPDT jack socket (i.e. this one ) in between pins 3->2 and pins 16->15, two situations can occur. If no jack plug is inserted, radio/cassete/cd signal is routed normally. If you insert jack plug into socket, this path is interrupted and signal from jack plug is routed to output. Usually, level of signal is lower, so you need to increase the volume.
How to make a connection?
- Unit part. Desolder capacitor beetween TDA7342 pins 3->2 and 16->15. As it is electrolytic type, don't forget to make a mark, where +/- side is (on mine unit pin 3 and 16 is +, pin 2 and 15 is -). Get a shielded cable with 4 wires (i.e. this one ). Solder white cable to + leg of capacitor, solder purple cable to hole leading to pin 3 on TDA7342 and solder - leg of capacitor back to hole leading to pin 2. Similarly light blue to + leg of capacitor, dark blue to hole leading to pin 16 and - leg of capacitor to hole leading to pin 15. Solder shielding wire to PCB ground.
- Jack socket part (see this link ). Solder white cable to pin 2, purple to pin 3, light blue to pin 5, dark blue to pin 4, shielding wire to pin 1.
- Check once again. You must have this connection: TDA7342 pin 3 -> purple wire -> jack pin 3 -> jack pin 2 ->white wire -> capacitor -> TDA7342 pin 2 and TDA7342 pin 16 -> dark blue wire -> jack pin 4 -> jack pin 5 ->light blue wire -> capacitor -> TDA7342 pin 15.
- You can put your jack socket wherever you want, i used CODE button as it is dummy one.