This project is spawned after playing around with some rfid tokens and scanners connected to an arduino. The idea came up to create a game for kids with it.
The basic principle of the game is to collect points, 'capture' stations or search for stations and then collect points using RFID tokens.
I am sure there are more games possible, including attaching stations with some puzzle to solve that report back to a basestation for instance.
The idea from a technical perspective should be easy:
Based on these points, this project is set up and still in progress. The current state of things is posted here.
- There are two or more scanner stations, and they should be self-contained.
- There has to be one station that keeps track of everything.
- The RFID tokens should be able to store some information, this might come in handy at some point.
To start with, there are some basic point to be able to run any game.
These points are:
- The scanner stations have to be battery operated.
- The controller is also preferred to be battery operated.
- The communication should be wireless.
- The setup should be easy to set up and control.
- There should be enough rfid tags available.
Since everything has to be battery operated, the arduino should be as clean as possible. For this purpose, the arduino pro mini 328 5V is used.
Because LED's use up power needlessly, these are removed from the PCB, as is the power regulator.
For programming them, a ttl to usb converter will be needed, but only one is needed to program them all.
Since the entire system should be able to work outdoors, a standard wifi connection won't do. For this, you need an accesspoint at least to make it work.
Also, since most internet routers these days have wifi on-board, the 2.4Ghz band is getting crowded and pretty soon the 5Ghz will also be.
There is also a distance issue. Especially in a crowded environment, the distance is restricted between the scanners and control station.
For these (and some other considerations) the standard wifi signal is not preferred.
Instead, the 422Mhz band is used. Not only does it carry further but it is also a lot les crowded.
For this, there is an excellent module available: the HC-12 module.
This module is capable of sending signals up to 1km away using the simple pigtail antenna at full power. To spare batteries, it is possible to lower the power output of the module.
Attaching an IPEX to SMA converter and an external antenna makes up for the loss of signal in part.
A test on only 10mW (the maximum allowed output in the Netherlands) yielded 500 meters range in the woods, more than enough for this purpose!
At full power, the person testing it had to walk to the next village before the signal dropped...
These modules do have one downside: there is no control on transmission. So no collision detection, error correction or any of the stuff wifi modules have, so the software running it will have
to take this into account.
Also, the data rate at long distance is best kept on the low side. Using it at 2400bps can't handle large volumes of data going around, so it's best to keep the number of bits sent and transmissions low.
For the rfid scanner, the MRFC522 module is used. It generally is delivered with one RFID card and one RFID token, but the waterproof tokens are available cheap in packs of 10 to 100 tokens.
If you shop around, you will find the modules for less than $3, tokens with 1kb onboard memory for about $10 for 50 of them.
Although the arduino and modules run on 5V, it is possible to power it using just 3 AA batteries. For this there are batteryholder available.
It will reduce range a little on the wireless communication, but it is not really noticable except when the batteries run out.
The scanner stations should be simple close boxes with indicators on it and an external antenna. In this case, 3 LED's are used: a red, green and yellow one.
All the batteries have to power are the LED's (which blink but do not light up constantly), the arduino, HC-12 and MRFC522 modules. So a batterypack of 2 AA batteries should give at least 10 hours of running time.
The control station has to do a lot more than any scanner station. Also, it is nice to have some sort of touchscreen on it to control things like starting a game, keep an overview of what's going on, count the scans per rfid, etc.
Because of this, 3 AA batteries is nowhere near enough to power it. Instead, a powerbank is used that will charge any modern phone at least once.
There are excellent ones available, but the one i use doesn't even have a switch on it, it switches on when you tap it!
Using that, the controller box doesn't even have to be opened to start it up (especially in a damp wooded environment this is a plus).
Also, the arduino itself needs to have more memory etc. to power the display, so for this an arduino mega 2560 is used with a touchscreen and HC-12 plus MRFC522 module.