How to measure the time my hand stays in front of an ultrasonic sensor?

[StefanL38]

Hi monsignore,
welcome to the arduino-forum.

There is a function that counts milliseconds. Up until it reaches 4.294.967.295 which is 49,7 days. Pretty long what ?

Long is a good keyword here. To work with this function you need a variable of type
unsigned long.

This function counting up milliseconds is called millis()
This is what you need here. And measuring time - your 10 seconds - is done with this function. Ten seconds are equal to 10000 milliseconds

here is a tutorial about timing based on function millis()

Example-code for timing based on millis() easier to understand through the use of example-numbers / avoiding delay()

non-blocking timing. Execute code only from time to time. There are a lot of different ways to learn programming. This thread wants to add another approach that is different to the yet existing ones. UPDATE 06.01.2023 if you are mainly interested in applying non-blocking timing you can do a quick read of this short tutorial / demonstration If you are intersted in understanding the details how it works go on reading here. I use an everyday analogon in this post to explain the basic principle …

best regards Stefan