An explanation of how the 74HC595 chip works as a serial-to-parallel converter, wired with just three pins to control eight Arduino outputs.
Getting to know membrane keypad types and the matrix principle that saves wiring pins with Arduino.
Sending and receiving text messages and making calls with the SIM800L module using AT commands, with a voltage-divider circuit to protect the module.
Getting to know the SIM800L module's components, power requirements, and pinout, as groundwork for using it practically with Arduino.