The Github download blues

[krismc]

I'm trying to setup a HX710 driver on an esp32. I downloaded the files from https://github.com/robert-hh/hx710 & put them in a 'hx710' folder on the esp32 then tried to run the first line of a sample program.

>>> from hx710 import HX710
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ImportError: no module named 'hx710.HX710'

So I'm thinking there is something about how github works that I don't understand? Is there some install process required rather than simply copying the files onto the esp32?

[davefes]

try:
from hx710_gpio import HX170
or
from hx710_pio import HX170
or
from hx710_spi import HX170

[robert-hh]

You could do it in different ways. Importing is always done from a directory contained in the sys.path list. So if you put you files into a hx710 directory, this directory must be added to sys.path. Usually, files like hx710 would be put into the lib directory, which is part of sys.path be default. So you have at least 3 options:

• add hx710 as the name o the directory to sys.path with import sys;sys.path.append("/hx710"). Then you can use e.g. from hx710_gpio import HX710. But: you cannot use from hx710 import HX710.
• move the file hx710_gpio.py (or any other of the hx710_xxx.py files) to the lib directory. Then you can use e.g. from hx710_gpio import HX710.
• keep the hx710 directory, but rename the hx710_xxx.py driver of your choice to __init__.py. Note that the hx710 directory itself must be in a place listed by sys.path. Then you can use e.g. from hx710 import HX710. hx710 is now the name of the directory.

All of that is standard Python behavior and not related to any specific module.

Note: Please prefer hx710_gpio.py or hx710_pio.py, as the return more precise values.

[krismc]

The print stmt I put in set_offset returns the same result as hx710.OFFSET. What I don't understand is why raw-oset is not the same as hx710.OFFSET?

>>> from hx710_pio import HX710; from machine import Pin; from time import sleep; pin_OUT = Pin(12, Pin.IN, pull=Pin.PULL_DOWN); pin_SCK = Pin(13, Pin.OUT); hx710 = HX710(pin_SCK, pin_OUT); hx710.tare()
offset 1531351.0
>>> for i in range(5): raw=hx710.read_average(); oset=int(hx710.get_value()); print(raw, hx710.OFFSET, oset, raw-oset); sleep(1)

1532029.0 1531351.0 575 1531454.0
1532006.0 1531351.0 593 1531413.0
1532056.0 1531351.0 498 1531558.0
1532011.0 1531351.0 555 1531456.0
1531589.0 1531351.0 484 1531105.0

[robert-hh]

What I don't understand is why raw-oset is not the same as hx710.OFFSET

hx710.OFFSET is the value returned by hx710.tare() and is kept at that value until hx710.tare() is called again. Both hx710.read_average() and hx710.get_value() perform internally hx710.read() (hx710.get_value() = hx710.read() - hx710.OFFSET). Due to sensor and conversion noise, every call of hx710.read() returns a different value, and so hx710.read_average() and hx710.get_value() change for every call.

[krismc]

Yeah I understand read_average & get_value vary each time but shouldn't the difference between them, hx710.OFFSET, be the same 1531351 each time since the tare is done only once at the start?

[robert-hh]

but shouldn't the difference between them, hx710.OFFSET, be the same 1531351 each time since the tare is done only once at the start

Why should it? hx710.OFFSET is the value of a read_average() at the time of calling hx710.tare(). Every call pf read_average() of get_value() will return a slightly different value, and so does tare(). Everytime you call hx710.tare(), hx710.OFFSET will change.

[krismc]

Are you saying then that there is a new tare done between each of the 5 readings in the example above?