Looking for small and cheap solution


I have a house with 3 floors and active cooling by my heat pump. I have no (de)centralized ventilation.

Now, I have set up several Temperature and Humidity sensors inside my house and of course also outside. I calculate absolute humidity and I have automations which are able to tell me if it makes sense to open a window in a certain room or not.

Of course, decentralized ventilators would be an elegant solution, but I do not have them.

My first idea was a plain and smart, battery powered led diode which could indicate by being switched on or off that it is needed to open or close a window. I did not find a suitable hardware.

I do not want active notifications on my smartphone for 10 rooms.
Neither do I want active acoustic signals.

I do have some 7,5" epapers set up with ESPHome for my PV and some other things, but the screens are already full with information.

So now I have the idea that maybe a very small screen would be

  • affordable
  • battery powered for a longer period
  • customizable

We are talking about a single device for each room and I do not want to spend too much money; in fact it would be enough if it could display only “open Window”. If humidty and temperature would also fit - great, but not necessarily needed.
It must not have active lighting and deep sleep for display driver and esp device should work properly for battery life purpose.

Any idea on a display/esp device/battery/housing combination?

Look into ESPHome.
It is based on cheap ESP devices and can handle led diodes as your first thought, but also a huge array of different displays.
Remember that displays can be a battery drain. ePaper displays are the best for batteries, but they come with some limitations, but also some benefit, like still showing the image on the screen, when the device is in deep sleep.
If you go with ePaper displays, instead of just a led diode, then the smaller ones usually have partial updates, which might be nice.

Only issue with ESPHome might be that a case.
If you have access to a 3D printer, then there will probably already be one for your project.
If you have no access to a printer, then a wide seelction of cases can be bought, but sometimes a box from something else might be used, like a the empty box that the cotton sticks came in.

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Thanks, I already run two 7,5 inch waveshare epapers with ESPHome.

I am a bit confused which displays, batteries and display drivers to buy for tge mentioned project. Any hints?

If you look at the ESPHome section for Waveshare displays, then it mention SPI in the configuration.
In the description below it also mentions a few moduls that can do partial update.
One such display is this one: https://www.waveshare.com/product/displays/e-paper/epaper-2/2.9inch-e-paper-module.htm

For battery you have several options.
I think maybe the easiest one is just connecting an USB powerbank, but 18650 batteries could be an option too, where the batteries then can be swapped for a fresh pair and the old ones can be charged somewhere else for next swap. There is also flat LiPo batteries, if need that.

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I now went for https://www.waveshare.com/wiki/2.13inch_e-Paper_Cloud_Module as an integrated module with battery onboard.
Will report back. However, I did not find a compatible housing yet.

Working fine! Will have to set them up now. For housing I ordered a 3d print from a thingiverse draft through craftcloud.