How to enable CD changer input on audi chorus I

How to enable CD changer input on audi chorus I

 From schematics, difrence between chorus and concert which has CD changer input,  is just few parts and enable CD-changer by coding as in here. Parts need to be soldered on main board to enable are this:

Audio input filter:

C1407 2.2uF/10V(THT, 2.54mm)

C1427 2.2uF/10V (THT, 2.54mm)

C1424 820pF (SMD 0805)

C1404 820pF (SMD 0805)

R1401 10kΩ (SMD 0805)

R1421 10kΩ (SMD 0805)

R1402 10kΩ (SMD 0805)

R1422 10kΩ (SMD 0805)

Location of all components on bottom side of PCB.

Power supply switch:

BSP452 (cheepest on ebay)

R2018 150Ω (SMD 0805)

Location of 150Ω resistor is on first picture.

Comunication lines Data-In, Data-out, clock

R5301 1kΩ (SMD 0805)

R5304 1kΩ (SMD 0805)

R5305 1kΩ (SMD 0805)

R5202  2,2kΩ (SMD 0805)

R5303  2,2kΩ (SMD 0805)

V5301 BC848B any BC848/850 is ok

 V5302 BZX84C5V6

V5303 BZX84C5V6

V5304 BZX84C5V6

Location of 3x1k and 2x2k2 is on first picture.

Price for this components is 0.68€ at gme.sk.

After this, you need CD changer emulator and simple circute, which emulate "mode" button press. For so small project is perfect attiny25/45/85 actualy 85 is cheapest one. For attiny support in arduino, follow this tutorial. Sketch for tiny:

code

Schematic  and pcb for this "mode button emulator":

schematics

PCB