lkasana / linux-hc-sro4

The HC-SRO4 is an ultrasonic distance sensor to be attached on 2 5V GPIO pins. This driver uses the interrupt logic of the GPIO driver to measure the distance in a non-blocking, precise and load-independend way. Unlike user land measurement methods you can even compile a linux kernel while doing measurements without getting weird results.

About

The HC-SRO4 is an ultrasonic distance sensor to be attached on 2 5V GPIO pins. This driver uses the interrupt logic of the GPIO driver to measure the distance in a non-blocking, precise and load-independend way. Unlike user land measurement methods you can even compile a linux kernel while doing measurements without getting weird results.

The driver has been tested using a Raspberry Pi 1, but in theory should work on any device that supports GPIO hardware.

Keep in mind that the HC-SRO4 is a 5 volts device so attatching it directly to the raspberry (3.3 Volts) pins is probably not a good idea. There are tutorials on the net explaining how to solder 2 resistors such that it works with the 3.3 Volts pins.

Building

You have two options to compile this driver for the Raspberry Pi:

• either compile it on a linux host using a cross development environment (recommended)
• or directly on the raspberry

To compile it using a cross development environment you'll need to install a cross development environment first (ARM cross compiler) and then obtain the raspberry pi kernel sources (these are different from the vanilla kernel), see https://www.raspberrypi.org/documentation/linux/kernel for instructions. Once the kernel is compiled and installed on the raspberry edit the Makefile of this repo so it says something like:

  CROSS_COMPILE=$(HOME)/raspberry/cross-dev/tools/arm-bcm2708/gcc-linaro-arm-linux-gnueabihf-raspbian-x64/bin/arm-linux-gnueabihf-
  KERNEL_DIR=$(HOME)/raspberry/linux

Type

  make 

and keep your fingers crossed ;) The result should be a file named hc-sro4.ko which is the linux kernel module to be inserted using:

  insmod hc-sro4.ko

on the raspberry.

Note that the kernel version running on the raspberry must match the version the module is built against, else insmod will not work.

Comiling on the raspberry is not recommended, since this requires either a kernel compile (takes hours) or using the kernel dev headers from the raspbian repo (which exists only for certain old kernels - this seems not to be supported).

If you need help compiling you may want to drop me a message, I'll be happy to help out.

Using the driver

Once insmod works, you'll find a new directory under /sys/class/distance (subject to change).

This supports an (in theory) unlimited number of HC-SRO4 devices. To add a device, do a (as root):

   # echo 23 24 1000 > /sys/class/distance-sensor/configure

(23 is the trigger GPIO, 24 is the echo GPIO and 1000 is a timeout in milliseconds)

Then a directory appears with a file measure in it. To measure, do a

   # cat /sys/class/distance-sensor/distance_23_24/measure

You'll receive the length of the echo signal in usecs. To convert (roughly) to centimeters multiply by 17150 and divide by 1e6.

To deconfigure the device, do a

   # echo -23 24 > /sys/class/distance-sensor/configure

(normally not needed).

That's all.

Enjoy and please Star this repo if you like it.

• Johannes