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Raspberry PiのPWMはアナログ音声出力と共用

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Raspberry PiのハードウェアPWMでサーボモータ… ではなく圧電サウンダ(ビープ音鳴らせるヤツ)を鳴らそうとしたところ,4極ジャックに繋いだスピーカからもビープ音が鳴るという奇妙な現象が.

日本語の情報が乏しいので英語の情報をあたると,PWMはアナログ音声出力と共用しているという記述を見つけました.

PWM and audio on RPi3 - Raspberry Pi Forums

Hardware PWM on the Pi uses the same peripheral as that used by the audio jack.
(意訳: ハードウェアPWMはオーディオジャックにも使われているぜ!)

現象の説明が付きます.
PWMと音声出力の両方を使用したい場合は,HDMIかUSBのオーディオデバイスを使うしかなさそうです.


Schematics - Raspberry Pi Documentation

公式の回路図を確認すると,4極ジャックの音声出力にはAUD_PWM0, AUD_PWM1がつながっていて,たしかに音声出力をPWMで実現しているようです.

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