Maybe I'm a little confused, but I found some remarks that the Arduino can't do 2 tasks at the same time. But it seems it can be done. Over the weekend I'll try to make it work, otherwise I will come back for some help.
Well, if you look deep down, it can only do one thing at a time..
But it's like a person. If you are making supper, you really can only do one thing at once, but you can get things going and set timers for some things, and manually check other things that are in progress.
You turn on the oven, setting it to a temperature, and start preparing the roast. When the roast is ready for the oven, you start preparing the vegetables. Oops.. the oven just beeped, indicating it's up to temperature, so you put the roast in, set a timer, and go back to preparing the vegetables. When the vegetables are ready, you start something else. All the while, you are glancing at the timer to see if it's time to start cooking the potatoes, or the vegetables, and so on.
You were multitasking, seemingly doing many things at once, but if you look at the process, you will see that you are only doing one thing at a time. The roast, while cooking, might need to be looked at, or basted, but you can't look into the oven while you are stirring the dessert, so you leave one task to do another, and come back to the task you left
Blink Without Delay is probably the first, and most important example of a technique you should learn well.