質問: 自動車のハンドブレーキ回路の電流検出 ![circuit](https://i.stack.imgur.com/zgn7r.png) Using Arduino, how can I detect that the switch is on? I have access to the wire within the red rectangle only. That's because the switch is closely connected to the car body (ground). When the handbrake is up, the switch is pushed by a coil to touch car body and close the circuit. And when the handbrake is down, the switch go away from the car body and the circuit is open. ![switch](https://i.stack.imgur.com/xsQkE.jpg)
回答: ワイヤーをフェライトか鉄心の周りに巻き付けて磁界を検出します。