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drivers/analog/hx711.c: Add driver for hx711 adc
Signed-off-by: Michał Łyszczek <michal.lyszczek@bofc.pl>
This commit is contained in:
Michał Łyszczek
committed by
Alan Carvalho de Assis
Alan Carvalho de Assis
parent
b634798bd6
commit
84a2cab886
@@ -0,0 +1,220 @@
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=============================
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HX711 ADC DESIGNED FOR SCALES
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=============================
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Driver contributed by Michał Łyszczek.
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HX711 is a 24bit ADC (Analog Digital Converter) designed for weight scales.
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This chip can be very slow. With internal oscillator and RATE pin pulled
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down, it outputs only 10 samples per second. To not hog down CPU, driver
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uses interrupt to detect when chip is ready. This will make read(2) blocking,
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but system can do whatever it needs before chip is ready. Because of that
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driver does not fully follow ADC API, but rather standard character device
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(read only).
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Values from tensometer can be easily read from shell with ``cat`` command
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.. code-block::
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cat /dev/hxx711_0
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Altough it may be better to dump values with example ``hx711`` program,
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since ``cat`` will just read until the end of time, and if ctrl+c is
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not working, it will steal shell forever.
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-------
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reading
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-------
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Reading is done by calling standard, posix, read(2) function. Only one value
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can be returned with single call to read(2). But an averaging function can
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be enabled, so that driver will read N samples, average them, and then will
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return single averaged value.
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This function accepts two types of buffer.
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If buffer is of size ``sizeof(int32_t)`` a int32 value will be stored in
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a buffer. If buffer size of bigger than ``sizeof(int32_t)`` function will
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store string representation of values in passed buffer.
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Simple code to read and print value may look like this
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.. code-block:: C
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int fd;
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fd = open("/dev/hx711_0", O_RDONLY);
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for (; ; )
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{
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int32_t value;
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value = read(fd, &value, sizeof(value));
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printf("Read: %"PRIi32"\n", value);
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}
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-----
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ioctl
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-----
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Since this chip (and driver) is designed for weight scale, kernel driver
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can provide some processing to make life easier for userspace code. These
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functions are implemented via ioctl(2) commands. In practice, non of these
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can be used, but if you just open driver and read it, you will get raw
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values from hx711 chip, which you will have to process yourself. If your
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needs are more standard, it's better to use kernel processing.
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HX711_SET_AVERAGE
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-----------------
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.. code-block:: C
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unsigned average = 5;
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ioctl(fd, HX711_SET_AVERAGE, average);
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Driver will read this number of samples from hx711 and will return average
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value of them all. To avoid corrupted data due to integer overflow, max
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average value that can be set is 225. If you need to average more values
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you will need to write your own code for that.
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HX711_SET_CHANNEL
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-----------------
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.. code-block:: C
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char channel = 'a';
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ioctl(fd, HX711_SET_CHANNEL, channel);
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HX711 has 2 channels, A and B, which can be swapped as necessary. Driver
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automatically performs dummy read, so that next call to read(2) will return
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value from new channel. When you switch to channel 'B', driver automatically
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changes gain to 32 (the only possible value). Going back to 'A' will set
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gain to 128.
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HX711_SET_GAIN
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--------------
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.. code-block:: C
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unsigned char gain = 128;
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ioctl(fd, HX711_SET_GAIN, gain);
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Set gain. Channel 'A' supports gain "128" and "64". Channel 'B' has only
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one gain option - 32.
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HX711_SET_VAL_PER_UNIT
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----------------------
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.. code-block:: C
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int val_per_unit = 813;
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ioctl(fd, HX711_SET_VAL_PER_UNIT, val_per_unit);
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Driver can perform calculations so that you can read physical values like
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grams, ounce or pounds, or your own artificial unit. You just need to specify
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what value from tensometer coresponds to one unit.
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Say you have tensometer that has max value of 1'000'000. Value 100'000 means
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1kg and sensor is fully linear. If you want to get readings in kg, you would
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set ``val_per_unit`` to 100'000. If you wanted output in grams, it would be
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value of 100. To have tenths of grams precision, you would set it to 10.
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Driver does not care about unit, you just pick one and stick to it.
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Note that driver can only return integers, so if you set it to return unit
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of kg, you will only get 1, 2, 3kg... and you won't be able to sense 0.5kg
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or 1.5kg. For that you would have to set value to 10'000, and driver would
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return you values of 15 (for 1.5kg) or 0.5 (for 0.5kg).
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HX711_TARE
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----------
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.. code-block:: C
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float precision = 0.1;
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ioctl(fd, HX711_TARE, &precision);
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Every scale needs a tare function. Driver polls hx711 for some time, and if
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it detects that scale is stable state, ioctl(2) will return with success,
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and next read(2) call will take new tare value into consideration when
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returning readings. Scale is assumed to be stable when several consecutive
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readings are (min-max values) are within specified precition.
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If ``HX711_SET_VAL_PER_UNIT`` was set prior to this, you can pass value
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in your unit. If you configured driver to work with grams, you can set
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this value to 0.1 (gram) or 5 (gram).
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If driver cannot get stable reading within some time, it will return with
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ETIME errno set.
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Important note, make sure you have set correct sign before taring, or
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else you will double your tare value instead of zeroing it!
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HX711_SIGN
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----------
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.. code-block:: C
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int sign = -1;
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ioctl(fd, HX711_SIGN, &sign);
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If values from drivers go lower when mass on scale goes higher you can swap
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the sign. This may be necessary when tensometer was installed upside down.
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---------------------
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hx711 example program
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---------------------
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There is also companion program in Application Configuration ---> Examples
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called ``HX711 driver example``. Main purpose of this is to show how to
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use the driver, but it also is a very good tool for quickly debuging chip
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from the shell, as it can dump readings and set all options.
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.. code-block::
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-h print this help message
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-d<path> path to hx711 device, default: /dev/hx711_0
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-t<prec> tares the scale with specified precision, might take few seconds to complete.
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If you set value per unit, precision is in units, otherwise it's raw values.
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If units are used, float can be passed like 0.1
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-v<val> value read that coresponds to one unit. This value has to be
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calibrated first before it's known
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-s reverse sign, if values decreses when mass increases, pass this
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-D dumps current device settings (like, average, channel, gain etc.)
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-a<avg> set how many samples should be averaged before returning value,
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values [1..225] are valid
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-c<chan> set channel to read (either 'a' or 'b' is valid)
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-g<gain> set adc gain, for channel 'a' 64 and 128 are valid,
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for channel 'b', only 64 is valid
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-r<num> read this number of samples before exiting, samples will be printed
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on stdout as string, one sample per line
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Set values are persistant, as in once set they are stored in driver and
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will be applied during execution of this program.
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If you specify only <-a|-c|-g|-v|-t> without -r, program will set new parameters
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and exit. You can later call program again only with -r option to read
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samples with previously set values. You can also pass all of them in one call
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To test if you require CONFIG_ADC_HX711_ADD_DELAY option set, run as:
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hx711 -a225 -r128
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This will load hx711 chip long enough to show any possible errors due to
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lack of added delay.
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Program executes in order: set options, tare, dump, run, so if you specify all
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options, new settings will be applied, then new settings will be printed
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and at the end program will tare the scale and print samples
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Examples:
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Set hx711 settings for first chip and exit:
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hx711 -a32 -ca -g64
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Dump chip settings from different chip
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hx711 -d/dev/hx711_2 -D
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Read 10 samples with previously set hx711 settings
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hx711 -r10
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Change channel and read 32 samples (average setting won't change):
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hx711 -cb -r32
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Set value per unit, to get output in grams, and then tare with 10g precision
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hx711 -v 813 -t 10
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@@ -61,6 +61,7 @@ Character device drivers have these properties:
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contactless.rst
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crypto/index.rst
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efuse.rst
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hx711.rst
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i2s.rst
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input/index.rst
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ipcc.rst
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@@ -91,6 +91,10 @@ if(CONFIG_ADC)
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if(CONFIG_ADC_LTC1867L)
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list(APPEND SRCS ltc1867l.c)
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endif()
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if(CONFIG_ADC_HX711)
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list(APPEND SRCS hx711.c)
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endif()
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endif()
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if(CONFIG_LMP92001)
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@@ -192,6 +192,43 @@ endchoice
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endif # ADC_MAX1161X
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config ADC_HX711
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bool "Avia Semiconductor HX711 support"
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default n
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---help---
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Enable driver to support Avia Semiconductor HX711 ADC
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designed for weight scales.
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Driver supports both 'a' and 'b' channels with 32, 64
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and 128 gain.
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Driver does not support continuous read and is not buffered.
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Driver uses interrupts to not hog the CPU while waiting
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for hx711 to be ready.
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if ADC_HX711
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config ADC_HA711_ADD_DELAY
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bool "Add 1us delay between clock pulses"
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default y if BOARD_LOOPSPERMSEC >= 15000
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---help---
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HX711 requires about 1us between clock pulses to work.
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This is not an issue on slower chips, but faster chips
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will most likely try to clock HX711 too fast, which
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will result in data lose.
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If this is enabled, code will insert 1us of delay to each
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clock change. Enable this only if you get data lose, or
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else you will just introduce unnecessary delay to your
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program.
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Best way to know if you need this, is to compile
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HX711 demo program and run it. If there are no errors
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reported during runtime, you can turn this of. If you
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see communication errors, then you should enable this.
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endif # ADC_HX711
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endif # ADC
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config COMP
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@@ -103,6 +103,10 @@ endif
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ifeq ($(CONFIG_ADC_LTC1867L),y)
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CSRCS += ltc1867l.c
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endif
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ifeq ($(CONFIG_ADC_HX711),y)
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CSRCS += hx711.c
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endif
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endif
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ifeq ($(CONFIG_LMP92001),y)
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File diff suppressed because it is too large
Load Diff
@@ -0,0 +1,212 @@
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/****************************************************************************
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* include/nuttx/analog/hx711.h
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*
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* Licensed to the Apache Software Foundation (ASF) under one or more
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* contributor license agreements. See the NOTICE file distributed with
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* this work for additional information regarding copyright ownership. The
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* ASF licenses this file to you under the Apache License, Version 2.0 (the
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* "License"); you may not use this file except in compliance with the
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* License. You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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* License for the specific language governing permissions and limitations
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* under the License.
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*
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****************************************************************************/
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/****************************************************************************
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* Included Files
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****************************************************************************/
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#include <nuttx/config.h>
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#include <nuttx/compiler.h>
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#include <nuttx/irq.h>
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/****************************************************************************
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* Pre-processor Definitions
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****************************************************************************/
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#define HX711_MAX_AVG_SAMPLES 225
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/* ioctl requests ***********************************************************/
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/* Set how many samples to read from hx711 to get a single averaged value.
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* Minimum value is 1. To prevent possible integer overflow, maximum value
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* is HX711_MAX_AVG_SAMPLES.
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*/
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#define HX711_SET_AVERAGE 0
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/* Set channel to use for next read() operation. Channels 'a' and 'b'
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* are available. Specify channel as 'a' character (0x61 hex)
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*/
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#define HX711_SET_CHANNEL 1
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/* Set gain to use for next read() operation. Channel 'b' only supports
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* gain of 32, and channel 'a' supports gain 128 and 64
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*/
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#define HX711_SET_GAIN 2
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/* Set what value coresponds to 1 unit. Takes integer.
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* If set to 0 (default) driver will return raw readings from
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* hx711 instead of calculated units.
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*/
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#define HX711_SET_VAL_PER_UNIT 3
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/* Depending on tensometer position, value will go higher or lower
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* (into negative values) when mass increases. If your sign does
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* not match, it can be changed by calling this.
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* 1 - no sign change (default)
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* -1 - sign will be changed
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*/
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#define HX711_SET_SIGN 4
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/* ioctl get functions */
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/* Get current average, pass pointer to unsigned int type */
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#define HX711_GET_AVERAGE 100
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/* Get current channel, pass pointer to single char */
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#define HX711_GET_CHANNEL 101
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/* Get current gain, pass pointer to single unsignedchar */
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#define HX711_GET_GAIN 102
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/* Get current value per unit */
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#define HX711_GET_VAL_PER_UNIT 103
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/* Tare the scale. Accepts int value with desired precision.
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* If HX711_VAL_PER_UNIT was set earlier, you should pass value
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* in units, otherwise you need to pass raw value as read from hx711.
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* Takes pointer to a float value.
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*/
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#define HX711_TARE 200
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/****************************************************************************
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* Public Types
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****************************************************************************/
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/* hx711 exposes 2 pins for communication. One is for data reading, and
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* second one is clock signal. This is similar to i2c but hx711 uses custom
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* protocol that is not compatible with i2c in any way.
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*
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* Platform code should provide these functions to manipulate these GPIOs
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*/
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struct hx711_lower_s
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{
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/**************************************************************************
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* Name: clock_set
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*
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* Description:
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* Sets underlying GPIO pin according to val.
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*
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* Input Parameters:
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* val - set GPIO pin high (1) or low (0)
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* minor - hx711 device being manipulated
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*
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* Returned Value:
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* OK on success, or negated errno on failure
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*
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**************************************************************************/
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CODE int (*clock_set)(unsigned char minor, int val);
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/**************************************************************************
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* Name: data_read
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*
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* Description:
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* Reads current value of data GPIO pin.
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*
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* Input Parameters:
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* minor - hx711 device being manipulated
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*
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* Returned Value:
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* For success, return 0 when GPIO is low, 1 when GPIO is high
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* or negated errno on failure.
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*
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**************************************************************************/
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CODE int (*data_read)(unsigned char minor);
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/**************************************************************************
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* Name: cleanup
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*
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* Description:
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* This function is called when last instance of minor is closed and
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* unlinked from fs so that hx711 minor instance is no longer available.
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* Platform should free all resources it allocated to register the
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* device.
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*
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* This function does not have to be set, if there is nothing to clean.
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*
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* Input Parameters:
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* minor - hx711 instance being destroyed
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*
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**************************************************************************/
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CODE void (*cleanup)(unsigned char minor);
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/**************************************************************************
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* Name: data_irq
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*
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* Description:
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* Setup (or tear down when handler is NULL) interrupt when data line
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* goes from HIGH to LOW state (falling edge).
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*
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* hx711 is slow, on internal oscillator and RATE=0 it takes 100ms to
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* sample a single reading. To avoid hogging CPU polling for data to
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* go down, driver will install interrupt handler before reading.
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* Once interrupt is received, driver will disable the handler.
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*
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* Input Parameters:
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* minor - hx711 device being manipulated
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* handler - function interrupt should call
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* arg - private data for handler, should be passed to handler
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*
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* Returned Value:
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* On successfull interrupt initialization 0 should be returned,
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* when there was failure initializing interrupt -1 shall be returned.
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*
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**************************************************************************/
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CODE int (*data_irq)(unsigned char minor, xcpt_t handler, void *arg);
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};
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/****************************************************************************
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* Public Functions Prototypes
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****************************************************************************/
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/****************************************************************************
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* Name: hx711_register
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*
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* Description:
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* Register new hx711 device in /dev/hx711_%d. Multiple hx711 can be
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* supported by providing different minor number. When driver calls
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* platform specific function, minor number is passed back, so platform
|
||||
* can know which hx711 is manipulated.
|
||||
*
|
||||
* Input Parameters:
|
||||
* minor - unique number identifying hx711 chip.
|
||||
* lower - provided by platform code to manipulate hx711 with platform
|
||||
* dependant functions>
|
||||
*
|
||||
* Returned Value:
|
||||
* OK on success, or negated errno on failure
|
||||
*
|
||||
****************************************************************************/
|
||||
|
||||
int hx711_register(unsigned char minor, FAR struct hx711_lower_s *lower);
|
||||
Reference in New Issue
Block a user