[driver] Add driver for Ultrasonic ranging module

[kevalpatel2106]

I have added driver for the ultrasonic ranging module to measure the distance of the object from the sensor. I have tested this driver using HC-SR04 ultrasonic sensor. It has simple implementation and a callback listener to get the distance value in centimeters.

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[kevalpatel2106]

I signed it!

[googlebot]

CLAs look good, thanks!

[kevalpatel2106]

Any plans to merge this PR?

[mangini]

@kevalpatel2106 , thanks for the PR. Are you getting reliable measurements using this driver? Android Things is not a real time OS, so there's no guarantee that a timing-sensitive protocol like the one in HCSR04 wouldn't be affected by competing threads/processes. We are working on a solution for it, and when we have it, we will work with you to review and add your driver to the official library. How does that sound?

[kevalpatel2106]

@mangini That sounds good. I am getting almost up to 4-5 cm accuracy with this driver. I am using it one of my DIY Robocar projects. To make it real time, I am spinning two different threads. One to send the pulses and another to get the echoes.

[mangini]

Great. You can define different thread priority, but it still won't be real time. I will keep this PR open until we have a better way of doing it.

[Fleker]

Good morning,
We've recently added a program to let developers submit drivers from their own repository to androidthings.withgoogle.com. Can you put this change in your own repository and then submit through that site?

[kevalpatel2106]

@Fleker Sure I will do it.