Arduino hc-sr04 code: example arduino sketch

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Arduino Sonar hc-sr04 codeI use the hc-sr04 for keeping my quadcopter at same altitude triggered by an added channel but also for automatic take-off and automatic landigs (still in progress). So i used this piece of code to initialize it and do some test. Is is good enough within 3,4 meters, not...
Arduino hc-sr04 code: example arduino sketch