main.c - source code
main.h - header file
Schematic_v1-0.png - adapter schematic
wd_we500c-d.pdf - phone schematic

Source code compiled with AVR Studio v4.18 + WinAVR for attiny45, optimization -O1.
SUT_CKSEL fuse should be programmed for external 8 Mhz crystal oscillator.

The converter originally designed to be mounted/wired inside the phone. 
It has to be connected in parallel to the phone line, but _after_ the hook switch, e.g. between terminals C and F/RR on the phone schematic. 
Rotary dial (all 4 wires) has to be disconnected from the phone and wired to the adapter (see schematic). 
The adapter is polarity sensitive.
Terminal C is just a solder pad, so I ended up using L2 instead (its a nice screw terminal).
