The Arduino Uno-compatible board has an MCS-51 (often called 8051 instead) instead of the usual ATmega328P/ATmega168. Specifically, [ElectroBoy] uses the AT89S52 .

A APC220 wireless module interface (serial/UART interface) Here is a circuit diagram of the multifunction shield adopted from the web (updated a bit by me). Looking up the schematic will save you a ...