Quantity   Component name
1 × ATmega328P-AU Microprocessors, Microcontrollers, DSPs / ARM, RISC-Based Microcontrollers
1 × DS1307Z+ Clock and Timer ICs / Real-Time Clocks
1 × 220nF ceramic capacitor 0805
1 × 2.2uF tantalum capacitor B-size
1 × 32.768kHz crystal 3216 metric size, 1206 imperial size
1 × 20x20 LED matrix I used GYXM-788ASR
1 × PCB 20x20 mm like the LED matrix | see GitHub or OSH Park links
1 × Laser printed transparency sheet to display the letters on top of the LED matrix
1 × SMD push button