Hello! My name is Evzen and I need help.
I have a project in school to create a device that will beneficial to people during the pandemic, so I went for a modified mailbox that sanitizes the package when put inside, but the problem is I dont know what items to use. Im new to this arduino stuff so Im asking for help
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Sorry to burst your bubble, but I doubt there is any evidence whatsoever to suggest transmission of Covid-19 through fomites in letterboxes.
Combined with the other potential problems of actually damaging the contents, I suggest you think of another project.
(I know they sell “smartphone sanitisers” using UV LEDs but I have great suspicions as to whether they could possibly generate sufficient UV-B to be effective. 
)
Hmm, the reply is great although sanitizing the products with the liquid or foam sanitizing will damage the material although the sanitizing of paper materials has to be done using the uv rays and although it is the complex one and need monetary investment. Work on these lines and think about the feasible one
As school project, and not intending to actually ever do anyone any good, you might be appropriately challenged to
You might program a duration for the rays and provide means to protect humans from exposure.
Do you think this would satisfy the teacher?
Detecting a package present
broken light beam (photocell detector)
or
weight on a platform (load cell or weight sensitive switch)
The rest is just code. Is programming part of your studies or something you are starting from scratch on your own?
It is a relatively easy program once you have the detection part, if is not something you are being taught it may be possible for you to learn just enough to hack your way through this by watching a tutorial series on youtube or working through the simple examples offered in the IDE.
a7
I can’t believe you need an Arduino for this.
You must not be an engineer. 
a7
If your mail is anything like mine, just replace the mailbox with a recycle bin. Problem solved.
-jim lee
Well, you don’t - a simple one-shot timer would suffice but …
Classic! 
The point is of course, to make a one-shot timer, you either get the parts and put them together or buy a module (I am sure there are plenty available) and in either case, do some work to set up the timing. Admittedly there are (cheap) digital timer modules available to do this and easy to configure.
The Arduino (Pro Mini) is (cheaply on Aliexpress) available as a module, programming it is just software and you can almost infinitely vary the behaviour, adding extra options and so on. It’s a good “go-to” module.