https://blog.gongquiz.com/2022/01/15/%eb%a7%8c%ec%9d%bc-%eb%82%b4%eb%b6%80-%ec%bd%94%ec%9d%bc-%ec%a0%80%ed%95%ad%ec%9d%b4-20%cf%89%ec%9d%b4%eb%9d%bc%eb%a9%b4-2khz-10v-%ec%a0%84%ec%9b%90%ec%97%90-%ec%97%b0%ea%b2%b0%eb%90%9c-30m/