Add HX711 absolute weight conversion #15292

ThomDietrich · 2022-04-04T19:49:02Z

Description:

Related issue (if applicable): fixes #13983

Implemented as discussed in issue ticket. Tested and working as expected.

Checklist:

The pull request is done against the latest development branch
Only relevant files were touched
Only one feature/fix was added per PR and the code change compiles without warnings
The code change is tested and works with Tasmota core ESP8266 V.2.7.4.9
The code change is tested and works with Tasmota core ESP32 V.2.0.3
I accept the CLA.

NOTE: The code change must pass CI tests. Your PR cannot be merged unless tests pass

ThomDietrich · 2022-04-04T19:57:00Z

tasmota/settings.h

-  uint32_t      keeloq_serial;             // FC4
-  uint32_t      keeloq_count;              // FC8
+  //uint32_t      keeloq_serial;             // FC4 TODO discuss
+  //uint32_t      keeloq_count;              // FC8 TODO discuss


This is not finished yet. Waiting for advise how to proceed.

This new functions needs two variables in permanent memory. The absolute weight is calculated from raw value following the formula

weight = absconv_a / 1e9 * raw + absconv_b / 1e6;

Typical config values from one of my setups are:

absconv_a = 953499

absconv_b = 15418390

The end result of the computation is a weight with a few decimals (e.g. 0-200kg, two decimals). The size of those variables can therefore certainly be reduced.

I am not sure about other builds and configs though. Another user could end with raw_weight values in different ranges and would need to apply a and b in lower or higher ranges. How do we avoid overflows and invalid user inputs?

Any help is highly appreciated.

I just made these variables available in settings.h

I think you need to find some kind of scaling to keep the values within the space of a uint32_t being 0 to 4.294.967.295 while keeping in mind results of calculation being also within this range. Using floats makes things worse as the float range is a lot smaller.

Thanks!

Okay let me think of a reasonable scaling

Having some difficulties wrapping my head around this.

weight = a * raw + b; weight = A / 1e9 * raw + B / 1e6; weight = absconv_a / 1e9 * raw + absconv_b / 1e6;

raw is currently of type long

absconv_a and absconv_b are of type long as well (meaning they are signed, which contradicts uint32_t)

absconv_b can be positive or negative, therefore signed long makes sense

the weight result realistically lies below 200kg and could also be negative when the setup is changed, lets say [-400..400]

Therefore, result of the calculation should always be within range, under reasonable parameters. How much sanity checking of these parameters do we need to implement?

Assuming weight results between [-400..400]:

we can likewise limit b to [-400..400]

we can limit a to something around 400 / max(long)

Not sure if this is the right way forward.

For reference, some of my setup configurations:

Just changed both absconv to int32_t (long)

I've played around with this and I wonder why we need such an elaborate formula.

Considering my situation. I have a loadcell which, when no load is attached results in a raw value of 1253. When I load a weight of known 280grams it returns a value of 1533. So all I need is a possibility to decrease the raw value with 1253 and I have the weigth.

What am I missing here?

Hey @arendst,
Did you go through the internal calibration process prior to this experiment?
Asking because I mostly ignore this function and use standard values for all my devices. In combination with the calibration formula (like examples given above) I have a deterministic approach to build reproducible devices. I have a dozend of these devices operational, number growing.

{"Sensor34":{"WeightRef":5000,"WeightCal":22,"WeightMax":200000,"WeightItem":0.0,"WeightChange":ON,"WeightDelta":10}}

I understand that all of this could feel like a solution that is not in line with functionality that is already there. My use case is to build devices which are calibrated and produce absolute weight measurements (10-90kg) across reboots, in permanent installations over years. The approach as described works quite satisfying for allmost two years now. However, so far the y=ax+b conversion is done in Home Assistant and I wanted to change that.

Should we discuss a different (more Tasmota integrated) approach?

Let's continue here #13983 (reply in thread)

tasmota/xsns_34_hx711.ino

arendst · 2022-04-05T08:27:26Z

tasmota/xsns_34_hx711.ino

@@ -441,6 +464,9 @@ void HxShow(bool json)
    }
    weight = (float)Hx.weight / 1000;                // kilograms
  }
+  if (Hx.absconv_a != 0 && Hx.absconv_b != 0) {
+    weight = (float)Hx.absconv_a / 1e9 * Hx.raw + (float)Hx.absconv_b / 1e6;
+  }


Am I right in the conclusion that using the raw value here makes current calibration efforts useless? How do you define the absconv parameters? By trial and error?

No you are correct. No offense, but I didn't find the implemented calibration combined with taring the weight upon startup useful for my use case (and wonder in which use case it is). The strategy I follow is to take a few raw weights for known masses, then run a simple linear regression, e.g. here: https://mycurvefit.com to get to the absconv parameters of y=ax+b.
It's not as integrated but is a good deterministic process. Let me know if you believe we should have a discussion about a different path!

My implemented use case is based on a commercial kitchen scale like the Ikea one.

After power on the user adds an empty dish, selects the reset button to zero the result and then is able to weigh anything he adds to the dish. Hence the zero button in the GUI.

There are ofcourse other uses which may use your suggested solution.

As your implementation doesn't interfere with mine I'll add it now so users can get some experience with it.

Interesting element you brought up!

USE_HX711_GUI is not defined for FIRMWARE_SENSORS. As a result I did never see this "zero button in GUI" you refered to. Maybe this should be changed?

@arendst ping in case you missed this.

Add commands ``Sensor34 10 <valueA>`` and ``Sensor34 11 <valueB>`` to use HX711 absolute weight conversion (#15292)

arendst · 2022-04-07T13:06:56Z

Merged for testing

- Add HX711 command ``Sensor34 10 0|1|<weight in gram>`` to set HX711 fixed tare (0 = use auto tare, 1 = use calibrated tare, Any other value is user selected tare) - HX711 removed command ``Sensor34 7`` as now active tare is persistent resulting in calculated current weight - Changed HX711 commands ``Sensor34 11 <valueA>`` and ``Sensor34 12 <valueB>`` to use HX711 absolute weight conversion (#15292)

ThomDietrich added 2 commits April 4, 2022 21:45

Add HX711 absolute weight conversion

4d57abe

Merge remote-tracking branch 'origin/development' into hx711-absconv

b986c06

ThomDietrich commented Apr 4, 2022

View reviewed changes

tasmota/xsns_34_hx711.ino Show resolved Hide resolved

arendst reviewed Apr 5, 2022

View reviewed changes

ThomDietrich added 2 commits April 5, 2022 19:33

Merge remote-tracking branch 'origin/development' into hx711-absconv

a6f1ed2

Remove memory allocation workaround

0981421

arendst added a commit that referenced this pull request Apr 7, 2022

Add Sensor34 commands

ccdd8c9

Add commands ``Sensor34 10 <valueA>`` and ``Sensor34 11 <valueB>`` to use HX711 absolute weight conversion (#15292)

arendst closed this Apr 7, 2022

ThomDietrich deleted the hx711-absconv branch April 8, 2022 11:56

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Add HX711 absolute weight conversion #15292

Add HX711 absolute weight conversion #15292

ThomDietrich commented Apr 4, 2022 •

edited

ThomDietrich Apr 4, 2022 •

edited

arendst Apr 5, 2022

ThomDietrich Apr 5, 2022 •

edited

ThomDietrich Apr 5, 2022 •

edited

arendst Apr 5, 2022

arendst Apr 8, 2022

ThomDietrich Apr 8, 2022

arendst Apr 8, 2022

arendst Apr 5, 2022

ThomDietrich Apr 5, 2022 •

edited

arendst Apr 7, 2022 •

edited

ThomDietrich Apr 8, 2022

ThomDietrich Apr 8, 2022

arendst commented Apr 7, 2022

Add HX711 absolute weight conversion #15292

Add HX711 absolute weight conversion #15292

Conversation

ThomDietrich commented Apr 4, 2022 • edited

Description:

Checklist:

ThomDietrich Apr 4, 2022 • edited

Choose a reason for hiding this comment

Choose a reason for hiding this comment

ThomDietrich Apr 5, 2022 • edited

Choose a reason for hiding this comment

ThomDietrich Apr 5, 2022 • edited

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

ThomDietrich Apr 5, 2022 • edited

Choose a reason for hiding this comment

arendst Apr 7, 2022 • edited

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

arendst commented Apr 7, 2022

ThomDietrich commented Apr 4, 2022 •

edited

ThomDietrich Apr 4, 2022 •

edited

ThomDietrich Apr 5, 2022 •

edited

ThomDietrich Apr 5, 2022 •

edited

ThomDietrich Apr 5, 2022 •

edited

arendst Apr 7, 2022 •

edited