This repository includes modifications to build Matthew Millman's modified rotary-to-dtmf firmware using Arduino IDE.
Arduino IDE (+ vscode) Arduino as ISP to upload the firmware to attiny85/atmega88/atmega8. Later I will add tutorials for the development environment.
attiny85 with 8Mhz crystal. (Change auc_frequency in dtmf.c and T0_OVERFLOW_PER_MS accordingly when the clock frequency are set differently.)
My main target phone is a Japanese model 600-A2.