This library is based on HX711 for Rasberry Pi using libgpiod instead of RPi.GPIO.
HX711 has a sevior timing requirement while reading data from DOUT. We have only 50us between 1 and 0 of PD_SCK pulse. Original hx711py library uses legacy/slow /sys/class/gpio interface with RPi.GPIO so that Jetson Nano violates 50us timing.
libgpiod is the solution using GPIO character device interface, it's faster than /sys/class/gpio interface. Let's use it!
Check example.py to see how it works.
You need to install libgpiod <=v1.6.x because newer version (v2.0) requires Linux kernel 5.5, but Jetson Nano's kernel version is 4.9.
sudo apt install autoconf-archive
git clone git://git.kernel.org/pub/scm/libs/libgpiod/libgpiod.git
cd libgpiod
git checkout v1.6.3 -b v1.6.3
./autogen.sh --enable-tools=yes --prefix=/usr/local --enable-bindings-python
make
sudo make install
You have to configure something to process libgpiod in user space.
- Add
/usr/local/libline to/etc/ld.so.conf.d/libgpiod.conf - Rebuild
/etc/ld.so.cacheas the below.
sudo ldconfig
- Add the line to
/etc/udev/rules.d/99-gpio.rulesas same as RPi.GPIO setting as the below.
SUBSYSTEM=="gpio", KERNEL=="gpiochip*", GROUP="gpio", MODE="0660"
- Reload udev.
sudo udevadm control --reload-rules && sudo udevadm trigger
- Confirm the group permission for gpiochips.
$ ll /dev/gpio*
crw-rw---- 1 root gpio 254, 0 Mar 24 15:53 /dev/gpiochip0
crw-rw---- 1 root gpio 254, 1 Mar 24 15:53 /dev/gpiochip1
- Clone or download and unpack this repository
- In the repository directory, run
python setup.py install
Channel A has selectable gain of 128 or 64. Using set_gain(128) or set_gain(64) selects channel A with the specified gain.
Using set_gain(32) selects channel B at the fixed gain of 32. The tare_B(), get_value_B() and get_weight_B() functions do this for you.
This info was obtained from an HX711 datasheet located at https://cdn.sparkfun.com/datasheets/Sensors/ForceFlex/hx711_english.pdf