board: 赤外線周波数を定数化

AVR Memory Usage
----------------
Device: atmega88

Program:    4156 bytes (50.7% Full)
(.text + .data + .bootloader)

Data:        102 bytes (10.0% Full)
(.data + .bss + .noinit)
board: 回路図を追加
board: フォトトランジスタを接続して明るさを取得できるように

AVR Memory Usage
----------------
Device: atmega88

Program:    4432 bytes (54.1% Full)
(.text + .data + .bootloader)

Data:        102 bytes (10.0% Full)
(.data + .bss + .noinit)