When you think about it, the design of this sensor is simultaneously fiendishly simple, and fantastically accurate and efficient. You send it a single 10us pulse (LOW to HIGH to LOW) to trigger a range ping. It sends the ping and immediately raises its Echo pin. The moment it confirms receipt of the echo, it drops Echo. You simply measure the time between Echo going LOW to HIGH and HIGH to LOW.

What I love about the simplicity is that the device doesn't need to measure that time itself, then translate that measurement into a serial communication of bits on the wire. Any computation or communication would take time and add to the cost of the part. By holding the Echo pin HIGH during the transit and dropping to LOW as soon as the audio echo is received, there's no latency in the report. True, it means the processor takes on the complexity of timing the pulse, but it has hardware that does that already, and why would I want to duplicate that capability in costly silicon?

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