Hello,
This is my project: a Pencil Case which tells you the number of pens in it and alerts you when there are pens missing so you dont lose pens, forget them or miss them ...
i dont know much about Arduino but i think that i am gonna add something that detects weight, so if you miss pens ==> the pencil case loses her normal weight and it alerts you.
When you're gonna put a new pen, you must tap a button which sets the new weight and makes it the normal one ...
the problem is what should i use to detect the pens, or their weight ?
I am new with arduino so If anyone has a better idea or wanna criticize or help with my project please tell me...
and thank you 
RFID is great for this. The "tag" on the pencil can be the same kind of thing as the security sticker you sometimes see on goods in a shop. Then you even know which pencil is missing.
Some aircraft maintenance shops use this for tool control. They can check that all the tools got back to the toolbox and weren't left inside the airplane. If one is lost then they take a handheld scanner into the plane to scan for RFID tags inside.
The problem with that soloution is that the only RFID system that can read multiple tags are UHF ones and these are expensive. SparkFun sell one of the cheapest
Your weight system might be hard to implement mechanically.
thank you guys ! i am new here so i needed some help 
thank you so much !
also the price wont be a problem for me
what do you think about the idea in general ?
what do you think about the idea in general ?
Not sure that knowing the number of pencils in a box is worth £400?
I have learnt a bit more about RFID... but i still dont undrestand why should I use a UHF reader ? can't I just use a HF reader, something like 13.56 Mhz ISO15693 protocol rfid reader, it support multiple tags reading and it's cheaper than the sparkfun one .
One metre or a bit less is enough for me i think ..
If there is another reason please tell me and try to explain it a bit for me
Thank you !
it support multiple tags reading
There are a limit to the number of tags that can be in the field at the same time. Also these tags arn't usually in foil type tags that can be unobtrusively wrapped round a pencil.
Ahmed_Gu:
something like 13.56 Mhz ISO15693 protocol rfid reader, it support multiple tags reading and it's cheaper than the sparkfun one.
It indeed supports multiple alternate tags, but you can only have one in the pencil box at any one time.
That would of course, make the problem much easier. 