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Topic # 147212 12-Jun-2014 14:44
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I want to make it so my nfc tags can act like a bus card (hop). I want to tap my phone to a tag and add or subtract a value from it.

Would like to use this as a easy way to monitor and track reward points in the classroom.

I don't want to use my tag to actually hop on a bus.

I've looked at the nfc writer apps but I can't seem to make it work

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Ultimate Geek
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  Reply # 1064172 12-Jun-2014 15:34
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I'm going to put this simply. This thread will go exactly the same way as the last thread you started.

You need a centralised server

Geoff E

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  Reply # 1064205 12-Jun-2014 16:45
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Ok, thanks.

It wasn't put that simply for me last time, a lot of yeah nahs.

Can you point me in the right direction for one of these?



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Ultimate Geek
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  Reply # 1064248 12-Jun-2014 17:24
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Its a big question.

Do you know how to code? If no you will likely be stuck I don't think I have seen to many open source projects for this type of thing.

A centralised server can be any computer. It just needs to be able to run code.

A raspberry pi is a good option it's cheap. Along with that you will want a Arduino. You could just do it with the raspberry pi but for simplicity we won't. Then you will need something to read the NFC cards like this.

You plug the NFC reader(after soldering the headers on) into the Arduino you plug in the Arduino into the Raspberry Pi via usb

This is just the Hardware part. Now for some software.
You need to have the following

A Database that will include Names, ID numbers, Allowance

You need to create a script that will read the card via serial(in linux the serial ports in linux are listed in /dev)
This script will need to keep polling the serial port for data. 
When data is received it then needs to know what to do with that data.

So you could create a user interface to tell it what you want to do with that data or you can create instruction cards that you scan before or after that tell it what action to take however you will need to guard these cards as in the wrong hands anything can be done.

Now if that all sounds to hard. It is. If it was simple then everyone would be doing it.

If this is your first time doing any coding. Then stop now. A system like this that is poorly developed is a really bad bloody nose waiting to happen. Think about the kid who knows something picks up someones card and wipes out all of their credits or takes there own card and gives them selfs tons of credit. Thats the sort of thing we are talking about here.

If you however know how to get software and hardware to gel then go right ahead if not find a student or find someone willing to develop this kind of system.

Geoff E

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  Reply # 1064266 12-Jun-2014 17:42
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Thanks for the great reply. I'll take a look into it. I haven't done any coding really but have many friends who do. I could call in a favor :)

Cheers for the info

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  Reply # 1100221 1-Aug-2014 17:47
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Unlocked the thread to post this..

Seems the idea was though of, and quickly quashed.

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  Reply # 1100242 1-Aug-2014 18:19
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Oblivian: Unlocked the thread to post this..

Seems the idea was though of, and quickly quashed.

The media using the word microchip makes everyone think its scary, When really its just an 'RFID card but on a wrist band, A good idea because if it was just a card students would be more likely to use it.

Sounds like an awesome idea, Imagine the uses, Library card, Attendance (students tap a reader when they enter the class)

People seem to think it can be used to track their location

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  Reply # 1117542 28-Aug-2014 21:07
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You don't need a centralised server, Arduinos or Raspberry Pis.

Your choices depend on the type of tags you want to use and the phone you want to read/write the tags with.

As I interpret it you have a small quantity of tag media and want to use a single phone to either

1. change the value on the tags themselves; or

2. remember the number of taps against each unique tag id on the phone itself

If you want to do the first you need media that you have the permission to write to, for example DESfire cards can be programmed to be used for reading and writing to. However they are not trivial to use securely and you can only formally get the APDU set by signing an NDA with NXP.

A second approach is to treat the DESfire card as an NDEF type 4 tag, there are phone applications that can format a blank DESfire card and create a tag. You can then use higher level libraries to perform the read/write of the NDEF tag. The API you use depends on the phone. 

If you want to do the read and write securely then the mobile phone will need access to the trusted keys.

The final cheap and cheerful approach is to simply use the phone to read the UID of the tag and remember the counts. 

The amount of security depends on how complex you want to make the system. Tags and simple cards can be cloned, true security requires mutual authentication where you don't trust a tag until the reader has validated the devices knowledge of secret keys. 

That all said, for a project that uses a Raspberry Pi and readily available reader, see nfcrsaps on sourceforge.

Also worth investigating libnfc.

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