Integrate absolute humidity calculation and display it beside temperature and relative humidity

[the78mole]

As relative humidity is already a good measure about moisture effect, absolute humidity (in g/m³) is sometimes much more important, since it does not change with temperature increase and decrease. In my special case, it is about the enclosure of my 3D printer and the drybox, where I would be able to directly read the absolute humidity at the device and not always need to ask my smart home GUI about.

The calculation is not very trivial, but with some simplifications, the it does not get too complex. I already wrote an article about this topic, which should be easily adaptable to the ATC firmware: https://the78mole.de/the-magic-of-absolute-humidity/

[pvvx]

The CPU in the thermometer does not have floating point or floating point libraries.

[the78mole]

OK, that is a valid point... Converting the calculations to fixed point is possible, but it takes some effort... If I find the time to have a deep dive into the sources and can setup the dev environment, I'll have a closer lookup.

[pvvx]

No worries. I've created various dew point conversion code variations over the decades. They are used in industrial installations. But they all require additional battery power. For that reason, I'm not integrating them into this project.

Requests for this feature are rare, but will require an increase in code size and consumption. Not everyone needs this.

[the78mole]

Couldn't it be an option on the settings page? But you are right, this still would require a bit of code size, even if it would not require power, if un-selected. Dew point would be also fine, because it is directly equivalent to the absolute humidity... and dew point is part of the BThome specification, while abs. humidity is not.

[davey]

I'd also love to see either dew point or absolute humidity coming directly from device (optionally) - if that's possible without too much additional power consumption (meaning reduced battery life). I wouldn't need that value too often, but once per minute would be really nice.

[michapr]

@davey - if you really need it (I think in home automation), why don't you calculate it yourself? I made it (as sample in Home Assistant) for the outdoor sensor and room sensors.

I think not every detail has to be calculated and sent by a hardware sensor. It is much more important to use energy resources sparingly in order to achieve the longest possible battery life.

[the78mole]

...as I wrote in the initial message, because I would like to have the information available, when I'm standing at the measurement location. When you start printing with clodes door, the inside temperature rises and therefore, the relative humidity is also decreasing rather quickly (obscuring the real informational value). When you open the door, the temperature decreases even faster, so the relative humidity does. To get any reasonable information from "changing environment" in this case, you need to read it directly at that location. Same appllies to using the thermometer devices e.g., in a fridge, a drybox,... You won't always look on your phone, to have an immediate information feedback.

[pvvx]

For this purpose, there is a function for displaying any values ​​on the thermometer screen. The function is integrated into ESPHome. *

This can be implemented on any BT adapter using a script, for example for HA. Search, maybe there are ready ones... The smartphone can also receive and transmit any values ​​to the thermometer for display.

• With a constant BLE connection to the thermometer, it is possible to achieve lower battery consumption by setting the BLE connection parameters with large internal periods. But this is not implemented in ESPHome and with frequent single BLE connections, battery consumption will be increased.

[the78mole]

That definitely sounds reasonable... Thanks!

[Ircama]

I tried to add the computation of the absolute humidity to the atc_mi_advertising GUI of the python-interface.

You can use a device supporting Python and Bluetooth to receive the advertisements from the thermometer and get the absolute humidity value.

Anyway, before pushing a contribution to the pvvx repository, I'd like to check that this addendum is correct.

@the78mole can you please verify whether the formula is correct and that the program produces valid data?

git clone https://github.com/Ircama/ATC_MiThermometer
git checkout ircama-absolute-humidity
cd ATC_MiThermometer/python-interface
pip3 install -r requirements.txt -r gui-requirements.txt
python3 -m atc_mi_interface.atc_mi_advertising

An alternative way to run it is via the precompiled atc_mi_advertising.exe Windows executable that can be extracted from the atc_mi_advertising.zip archive after downloading it from Releases.

[the78mole]

Looks good, but I'm not absolutetely sure, if 2.1674 is missing a factor of 100. In my calculation, I use 216.7. But I can not currently test it in reality. I'm totally loaded with other work and the vacation trip is getting closer and closer.

PS: Your calculations are introducing floating point stuff and math (exp) libs. Doesn't it blow up program space and eat up battery?

BTW @pvvx: The "workaround" with calculation in some HA template and ESPhome-based BLE GATT displaying on the sensor does not work. ESP tells, it is sending the information to the Mi, but it does not show up on there... I also can not find any setting in the Telink Flasher Web App to enable it, only enabling/disabling battery and clock.

[pvvx]

No settings are required on the thermometer. Display is performed by command 0x22 + data structure. TelinkMiFlasher has a function of demonstrating the display of arbitrary numbers and additional symbols:

There is also a function of direct display of bit data on the LCD display. That is, control of display of each pixel...

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ESP tells, it is sending the information to the Mi, but it does not show up on there...

I don't use ESPHome. If something doesn't work there, please direct your questions to the appropriate topics.

To avoid such uncertainties, the expansion of the thermometer functionality is limited to basic functions, and the formats of the basic functions have been fixed for more than 2 years. Additions are possible only by assembling the firmware with your own version. But you should not expect support for your own additions. Typically it takes between 9 months and several years for communities on the topics described to distribute and support add-ons.

[Ircama]

if 2.1674 is missing a factor of 100. In my calculation, I use 216.7.

I'll leave the code there for some time for testing/peer review. That constant looks right to me. I think yours might need fractions of humidity units, not values between 0 and 100.

Your calculations are introducing floating point stuff and math (exp) libs. Doesn't it blow up program space and eat up battery?

No, it doesn't. This app is external to the thermometer (e.g., Windows program) and communicates via BLE.

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An alternative way to transmit digits to the LCD is via the -n option of atc_mi_config.exe (command-line tool):

  -n CSV_STRING, --numbers CSV_STRING
                        Send 6 digits to LCD in the form "1,2,3,_,4,5" or "0xf5,0x05,..."