Counter reference materials

This package contains the added 00-99 counter reference files:

- up_down_counter_tables_00_to_99_led_control_all_pin_meanings (1).pdf
- assets/up-down-counter-signal-flow.png
- assets/seven-segment-digit-patterns.png
- assets/seven-segment-display-pinout.png
- assets/seven-segment-ssd-configuration.jpg

Online session links:

- Session 01: https://youtu.be/2jxMAc5UnNQ
- Stage 2 recording: https://youtu.be/1D6mOojhSX8

The YouTube recordings are linked here rather than included as video files.
