Notice that in the video and in some of the pictures I have that 3xAA battery pack at the back. It is meant to power the whole thermometer when the power jack is not connected. The user just has to flip the switch on and it should work normally. It seems like I made a design mistake and it will not work with a 4.5V input, because of the voltage dropout on the linear power supplies. For some reasons, the actual dropout in the voltage is more than 1V on both the input diode and the LM317 and at the input of the 1117 I get less than 3V. This is not enough for powering the microcontroller so it doesn't work. If you want to replicate this project, you will have to replace the battery pack with a 9V battery holder.
This is also very ironic, considering the level of engineering I aim for in this project. Lol. Mistakes happen and I guess this is exactly the kind of trial an error that propel us forward.