Full schematic/source code coming soon!
Highlights for now:
- Used phone's original keypad, receiver, and "hook"
- Logic/Audio controlled with a Sparkfun RP2040 Thing Plus running CircuitPython.
- 3 voices for audio: button/status tones, recorded messages, and ringer.
- All audio fed out to UDA1334A breakout from Adafruit (I2S DAC)
- All audio split out to two outputs: the receiver earpice, and a 3W speaker driven by PAM302 class D amp (breakout from Adafruit).
- The amplifier has an enable pin, which is only pulled high when the ringer audio is playing. So all audio goes through the earpiece, but only the ringer goes through the amplified speaker!