I have been testing the only prototype I currently have for about 6 weeks and it runs without any problems.

I have also calibrated the temperature sensor and it looks like there is constant error of -0.6 °C from the actual temperature (in range from 20 to 60 °C) when reading from LM35DZ with the internal voltage reference. That is actually quite nice. I don't need to use the external voltage reference.

I have also drawn the front panel and my friend 3D printed it for me.