1、物料

  • Raspberry 4B

image.png

  • 单点式称重传感器

image.png

  • HX711

image.png

2、接线方法：

称重传感器有根线，白黑红绿分别为：

红 ———-> E+ 黑 ———-> E- 白 ———-> A+ 绿 ———-> A-

称重传感器接HX711，如下图所示，传感器 红黑白绿；网上还有很多种接法，都试过之后，只有这种是稳定的；
image.png

HX711接树莓派接法如下图：
image.png
保证接线稳定后，打开树莓派建立Demo测试；

3、Demo

hx711.py

  1. """
  2. HX711 Load cell amplifier Python Library
  3. Original source: https://gist.github.com/underdoeg/98a38b54f889fce2b237
  4. Documentation source: https://github.com/aguegu/ardulibs/tree/master/hx711
  5. Adapted by 2017 Jiri Dohnalek
  7. This program is free software; you can redistribute it and/or modify
  8. it under the terms of the GNU General Public License as published by
  9. the Free Software Foundation; either version 2 of the License, or
  10. (at your option) any later version.
  12. This program is distributed in the hope that it will be useful,
  13. but WITHOUT ANY WARRANTY; without even the implied warranty of
  14. MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15. GNU General Public License for more details.
  17. You should have received a copy of the GNU General Public License along
  18. with this program; if not, write to the Free Software Foundation, Inc.,
  19. 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  20. """
  23. import RPi.GPIO as GPIO
  24. import time
  25. import sys
  28. class HX711:
  30.     def __init__(self, dout, pd_sck, gain=128):
  31.         """
  32.         Set GPIO Mode, and pin for communication with HX711
  33.         :param dout: Serial Data Output pin
  34.         :param pd_sck: Power Down and Serial Clock Input pin
  35.         :param gain: set gain 128, 64, 32
  36.         """
  37.         self.GAIN = 0
  38.         self.OFFSET = 0
  39.         self.SCALE = 1
  41.         # Setup the gpio pin numbering system
  42.         GPIO.setmode(GPIO.BCM)
  44.         # Set the pin numbers
  45.         self.PD_SCK = pd_sck
  46.         self.DOUT = dout
  48.         # Setup the GPIO Pin as output
  49.         GPIO.setup(self.PD_SCK, GPIO.OUT)
  51.         # Setup the GPIO Pin as input
  52.         GPIO.setup(self.DOUT, GPIO.IN)
  54.         # Power up the chip
  55.         self.power_up()
  56.         self.set_gain(gain)
  58.     def set_gain(self, gain=128):
  60.         try:
  61.             if gain is 128:
  62.                 self.GAIN = 3
  63.             elif gain is 64:
  64.                 self.GAIN = 2
  65.             elif gain is 32:
  66.                 self.GAIN = 1
  67.         except:
  68.             self.GAIN = 3  # Sets default GAIN at 128
  70.         GPIO.output(self.PD_SCK, False)
  71.         self.read()
  73.     def set_scale(self, scale):
  74.         """
  75.         Set scale
  76.         :param scale, scale
  77.         """
  78.         self.SCALE = scale
  80.     def set_offset(self, offset):
  81.         """
  82.         Set the offset
  83.         :param offset: offset
  84.         """
  85.         self.OFFSET = offset
  87.     def get_scale(self):
  88.         """
  89.         Returns value of scale
  90.         """
  91.         return self.SCALE
  93.     def get_offset(self):
  94.         """
  95.         Returns value of offset
  96.         """
  97.         return self.OFFSET
  99.     def read(self):
  100.         """
  101.         Read data from the HX711 chip
  102.         :param void
  103.         :return reading from the HX711
  104.         """
  106.         # Control if the chip is ready
  107.         while not (GPIO.input(self.DOUT) == 0):
  108.             # Uncommenting the print below results in noisy output
  109.             # print("No input from HX711.")
  110.             pass
  112.         # Original C source code ported to Python as described in datasheet
  113.         # https://cdn.sparkfun.com/datasheets/Sensors/ForceFlex/hx711_english.pdf
  114.         # Output from python matched the output of
  115.         # different HX711 Arduino library example
  116.         # Lastly, behaviour matches while applying pressure
  117.         # Please see page 8 of the PDF document
  119.         count = 0
  121.         for i in range(24):
  122.             GPIO.output(self.PD_SCK, True)
  123.             count = count << 1
  124.             GPIO.output(self.PD_SCK, False)
  125.             if(GPIO.input(self.DOUT)):
  126.                 count += 1
  128.         GPIO.output(self.PD_SCK, True)
  129.         count = count ^ 0x800000
  130.         GPIO.output(self.PD_SCK, False)
  132.         # set channel and gain factor for next reading
  133.         for i in range(self.GAIN):
  134.             GPIO.output(self.PD_SCK, True)
  135.             GPIO.output(self.PD_SCK, False)
  137.         return count
  139.     def read_average(self, times=16):
  140.         """
  141.         Calculate average value from
  142.         :param times: measure x amount of time to get average
  143.         """
  144.         sum = 0
  145.         for i in range(times):
  146.             sum += self.read()
  147.         return sum / times
  149.     def get_grams(self, times=16):
  150.         """
  151.         :param times: Set value to calculate average, 
  152.         be aware that high number of times will have a 
  153.         slower runtime speed.        
  154.         :return float weight in grams
  155.         """
  156.         value = (self.read_average(times) - self.OFFSET)
  157.         grams = (value / self.SCALE)
  158.         return grams
  160.     def tare(self, times=16):
  161.         """
  162.         Tare functionality fpr calibration
  163.         :param times: set value to calculate average
  164.         """
  165.         sum = self.read_average(times)
  166.         self.set_offset(sum)
  168.     def power_down(self):
  169.         """
  170.         Power the chip down
  171.         """
  172.         GPIO.output(self.PD_SCK, False)
  173.         GPIO.output(self.PD_SCK, True)
  175.     def power_up(self):
  176.         """
  177.         Power the chip up
  178.         """
  179.         GPIO.output(self.PD_SCK, False)

example_python3.py

  1. """
  2. HX711 Load cell amplifier Python Library
  3. Original source: https://gist.github.com/underdoeg/98a38b54f889fce2b237
  4. Documentation source: https://github.com/aguegu/ardulibs/tree/master/hx711
  5. Adapted by 2017 Jiri Dohnalek
  7. This program is free software; you can redistribute it and/or modify
  8. it under the terms of the GNU General Public License as published by
  9. the Free Software Foundation; either version 2 of the License, or
  10. (at your option) any later version.
  12. This program is distributed in the hope that it will be useful,
  13. but WITHOUT ANY WARRANTY; without even the implied warranty of
  14. MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15. GNU General Public License for more details.
  17. You should have received a copy of the GNU General Public License along
  18. with this program; if not, write to the Free Software Foundation, Inc.,
  19. 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  22. ##################
  23. PYTHON 3 EXAMPLE
  25. This version of example is python 3 compatible
  26. and outputs weight in grams.
  28. Make sure you enter the correct values for offset and scale!
  29. Also, don't forget to set the correct gain, default is 128.
  30. """
  32. import RPi.GPIO as GPIO
  33. import time
  34. import sys
  35. from hx711 import HX711
  37. # Force Python 3 ###########################################################
  39. if sys.version_info[0] != 3:
  40.     raise Exception("Python 3 is required.")
  42. ############################################################################
  45. hx = HX711(5, 6)
  48. def cleanAndExit():
  49.     print("Cleaning...")
  50.     GPIO.cleanup()
  51.     print("Bye!")
  52.     sys.exit()
  55. def setup():
  56.     """
  57.     code run once
  58.     """
  59.     hx.set_offset(`Place offset here`)
  60.     hx.set_scale(`Place ratio here`)
  63. def loop():
  64.     """
  65.     code run continuosly
  66.     """
  68.     try:
  69.         val = hx.get_grams()
  70.         print(val)
  72.         hx.power_down()
  73.         time.sleep(.001)
  74.         hx.power_up()
  76.         time.sleep(2)
  77.     except (KeyboardInterrupt, SystemExit):
  78.         cleanAndExit()
  81. ##################################
  83. if __name__ == "__main__":
  85.     setup()
  86.     while True:
  87.         loop()

以上代码摘自Github，https://github.com/learn2develop/hx711py

Python library for the HX711 load cell amplifier and Raspberry Pi

在树莓派中执行

  1. git clone https://github.com/learn2develop/hx711py.git
  3. cd hx711py

如何校准
1、在树莓派中运行calibration.py 

  1. python3 calibration.py

按照顺序开始，首先清空秤盘，回车
在秤盘上放一个已知重量的东西，如2KG的水瓶，回车
提示输入已知物重量，输入2000，回车
程序会自动计算出offset、scacle这两个值，如：Offset: 8252194.375 Scale: -27.108333333333334复制下来
2、修改example文件，如使用Python3，则修改example_python3.py,

  1. vim example_python3.py

修改代码中

  1.  hx.set_offset(`Place offset here`)
  2.  hx.set_scale(`Place ratio here`)

为

  1. hx.set_offset(8252194.375)
  2. hx.set_scale(-27.108333333333334)

然后运行代码测试效果

  1. python example_python3.py,

数值有点偏移，跟接线以及校准有问题，逐步改进中

本人小白一枚，如有共同爱好或者遇到同样问题欢迎沟通交流，QQ：1078246446