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mynewt_hc-sr04

A simple test library to connect a HC-sr04 ultrasonic distance sensor the mynewt core platform.

Including in your mynewt project.

Add the following repository descriptor to your project.yml file

    repository.mynewt_hc-sr04:
        type: github
        vers: 0-latest
        user: paulfdietrich
        repo: mynewt_hc-sr04

and include the following in your project.repositories variable

    project.repositories:
        - apache-mynewt-core
        - mynewt_hc-sr04

Add the following dependency to your application's (or whatever uses this library) pkg.yml file.

    pkg.deps:
        ...
        - "@mynewt_hc-sr04/libs/hc-sr04"

Limitations

This was mostly just a test library so I could test creating packages, projects, and repositories. It has some severe limitations

  • It can only control one device per build
  • It relies on polling GPI and GPO for timing

Usage

Include files

Add the include path #include <hcsr04/hcsr04.h> to files that are using the library.

hcsr04_init

    void hcsr04_init(void);

Initializes the library to talk to the sensor. The sensor is expected to be attached to two port pins, which you must define in your BSP. This must be called once. A good place is main before you start the OS.

hcsr04_measure_distance

Return the distance in centimeters of the object near your HC-SR04. If a reading is not possible or the object is too far away, -1 is returned.

    int hcsr04_measure_distance(void);

This function blocks while taking a reading from the device.

Unresolved Externals

You will get several unresolved externals when building this. Ensure that your BSP defines the following variables:

    int hcsr04_trigger_pin = MY_TRIGGER_PIN;
    int hcsr04_echo_pin = MY_ECHO_PIN;

Of course, replace MY_XXX with the trigger and echo pins you are using in your project.