吐槽一下，LZ的C代码，和Arduino全C++的库格格不入。

Playground的NewPing库
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Methods

sonar.ping(); - Send a ping, returns the echo time in microseconds or 0 (zero) if no ping echo within set distance limit
sonar.ping_in(); - Send a ping, returns the distance in inches or 0 (zero) if no ping echo within set distance limit
sonar.ping_cm(); - Send a ping, returns the distance in centimeters or 0 (zero) if no ping echo within set distance limit
sonar.ping_median(iterations); - Do multiple pings (default=5), discard out of range pings and return median in microseconds
sonar.convert_in(echoTime); - Converts microseconds to distance in inches
sonar.convert_cm(echoTime); - Converts microseconds to distance in centimeters
sonar.ping_timer(function); - Send a ping and call function to test if ping is complete.
sonar.check_timer(); - Check if ping has returned within the set distance limit.
timer_us(frequency, function); - Call function every frequency microseconds.
timer_ms(frequency, function); - Call function every frequency milliseconds.
timer_stop(); - Stop the timer.