ディラン @dleung513 https://mobile.twitter.com/dleung513/status/1493829569626865666
PWM and a Buzzer
http://jallib.blogspot.com/2009/02/step-by-step-having-fun-with-pwm-and_14.html
Simple Circuit Communicates Over Low-Voltage Power Lines
https://www.electronicdesign.com/technologies/communications/article/21799727/simple-circuit-communicates-over-lowvoltage-power-lines
