Postmortem of my 5 minute Wind Tunnel experiment.

(1) 12V 700mA CPU fan wind speed is too low.

(2) 500g Load Cell not sensitive enough. Should consider 100g Load Cell next time.

Now I am going back to my hx711 test program v0.3. I found the first bug in the PyPi hx711 library. It appears to be a typo error. But as the wise man *Warren Buffett says, "There ain't be just one cockroach in the kitchen. So I am expecting more bugs or incompatibility of the PyPi library with the Rpi Thonny library. So I am read the library more closely, just in case I need to troubleshooting:

This is the full listing fo the pypi hx711 library. It is less than 300 line long. So should be easy to debug.

# ******************************************************************************************
# Program description
#   hx711test03.py tlfong01 2020oct28hkt2201
# System Config
#   Rpi4B 2GB buster Thonny python 3.7.3
# HX711 PyPi Library Install
#   pi@raspberrypi:~ $ date | Tue 27 Oct 2020 09:14:01 PM HKT
#   pi@raspberrypi:~ $ uname -a | Linux raspberrypi 4.19.118-v7l+ #1311 SMP
#     Mon Apr 27 14:26:42 BST 2020 armv7l GNU/Linux
#   pi@raspberrypi:~ $ pip3 install hx711
#     Looking in indexes: pypi.org/simple, piwheels.org/simple

I am also making a penzu pypi hx711 library reading and testing log.

penzu.com/p/340557f4

I am also considering the Arduino Library of HX711. I don;t have much confidence on the PyPi hx711 Library, because I already found a bug in the demo program. Now I googled the Arduino Library to check out if it is good. The links are listed below.

One thing I worry about the Arduino hx711 library is the following remark in the documentation:

This might be a program for me using more that two hx711 modules. The Rpi version can use multi-threading and can execute two hx711's in parallel, therefore should be more time efficient.

The Arduino hx711 library is compatible to the following architectures:

I am particularly interested in (d), ie:

Arduino core for STM32 (STM32 F1 (Cortex-M3): STM32F103C8T6 STM32 Blue Pill Board)

But I only know Arduino UNO and nothing about STM32 (Though I know ESP8266 WeMos D1 Mini, but found its microPython a bit slow). So my contingency plan is to switch to STM32, in case I get stuck in PyPi hx711 library and have to give up.

Now I am thinking of ordering a couple of mini 100g digital weight scale from TaoBao. My objective is NOT to use the scale, but to tear it down and get the 100 get load cell with the attached stainless plate to hold the loading.

This is my STM32 and Arduino 2 in 1 board, ordered and already arrived a couple of weeks ago, now standing by, ready to take over as soon as Rpi PiPy python ht711 library fails.

Now I am coming back to PyPi hx711 library package. As I said earlier, the complete library is only some 300 lines long, and only a couple of main functions, such as reset, getRawData, conver to decimal etc. I have written a penzu reading log as I read the program listing.

PyPi hx711 library penzu reading log: penzu.com/p/bb7ed5c8.

I am reading my penzu hx711 library reading log a second time, make sure I have not missed reading any important functions. penzu.com/p/bb7ed5c8

The time has come to use the library functions to reset hx711 and read results.

Afternoon tea time. Taking a long break.

Now I have written and debugged testHx711v04b. This program tests hx711 measuring only One hx711 module's Channel A with a 500g LoadCell loaded with 250g. Multimeter measures 2.6mV, and average of 8 measurements is 885762. The complete listing of the program with a sample output is shown below.

# Program description
#   hx711test04a.py tlfong01 2020oct29hkt2113
# System Config
#   Rpi4B 2GB buster Thonny python 3.7.3
# HX711 PyPi Library Install
#   pi@raspberrypi:~ $ date | Tue 27 Oct 2020 09:14:01 PM HKT
#   pi@raspberrypi:~ $ uname -a | Linux raspberrypi 4.19.118-v7l+ #1311 SMP
#     Mon Apr 27 14:26:42 BST 2020 armv7l GNU/Linux
#   pi@raspberrypi:~ $ pip3 install hx711
#     Looking in indexes: pypi.org/simple, piwheels.org/simple
#     Requirement already satisfied: hx711 in ./.local/lib/python3.7/site-packages (1.1.2.3)

@Cem I have written and debugged my test program v0.4b. As I said, I am making things as simple as possible: Just one hx711 module, using only Channel A, using a single loading of 250g to the 500g load cell, only raw results, no tare. Multimeter for the 250g load is 2.6mV, and the average of 8 hx711 measurements is 885765. If you like to try it, the procedure is just two steps:

(1) Install by pip3 the PiPy hx711 library,

(2) Copy, paste and run hx711 test version v0.4b. If you get the results average 88xxxx, that means everything goes well.