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Topic: library capacity counter (Read 2917 times) previous topic - next topic


Hello to all, We're going to make a library capacity counter, all it does is to display "open", when the library is not full, otherwise "Full" when there is no vacant seats. At the same time, there is a counter display,. the counter would increment if someone goes IN and decrement if someone goes OUT.. what's the best sensor to use that would trigger the counter to count? are we going to use LED for the display? cud you give as related ideas about capacity counter. I've research about this but i only found few. 

help as.....
cansas warrior



Can you describe the library a little more please.  Is the same door used for both in and out? Does everyone who enters the library use a seat ?  Do library users have to swipe or other identification method on entry?

"There is no problem so bad you can't make it worse" - retired astronaut Chris Hadfield


The normal way to count people into/out of a room is with a light beam and two sensors at the door. However this method is fraught with problems and not very reliable.

Now if people have to swipe an RFID card or something that's a different matter.

Rob Gray aka the GRAYnomad www.robgray.com


there are two doors, one for IN and one for Out.. the door is not a slide door..... we do have an identification card, a library card but we are not going to swipe it.. there's someone who'll check for it, if we bring it then we can pass... do you think using RFID is good to use.. i wud like also to add in our project, to record data,m the who in and the time in... cud it be possible?? please help..
cansas warrior


I have no experience with RFID but I think it would be a reasonably reliable way to count as long as people scanned there card on exit as well.

No matter what you do there will be situations where the count is wrong if you use a computer, there are just too many ways stuff the count up.

There may be another method but the only reliable way I can think of is using turnstiles that force people to go through one at a time.

Rob Gray aka the GRAYnomad www.robgray.com


There are plenty of sensors which detect people walking past.    Look for sensors used for the doorway of shops.

But if you actually want to count people,  not very reliable.   A person who swings their arms when they walk may count as two.   Two people walking side by side may count as one.

You need a very narrow door with a chute to force people to walk past one at a time.


Just thinking out loud... what about combining two sensors, like a weight detector / floor-hidden switch and a laser/ir beam ?

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