Montag, 4. Februar 2013

4. The guts of the DuinoSqueeze

In the overview diagram of yesterday, I listed the required modules. In the following picture you can see them in all its glory.

From the left: The Ethernet Shield, the Arduino Uno and the RFID-card

The Arduino Uno
To this module it is to say the least because this is the best known on the net. I purchased my Uno from China and it works properly me until now. I'm still thinking about whether or not it should give way to a lack of space to a Nano. I would suggest that we decide this at a later date, when the DuinoSqueeze runs.

The Ethernet Shield
As well a board from China. The most famous two Ethernet Shields have either the ENC28J60 or WIZnet W5100 chip installed. I opted for the Wiznet-variant, because it is easier to handle. The Shield will be mounted piggyback on the Arduino. Arduino and the Ethernet-shield operates together via the SPI interface.

The RFID Shield 
I do not intend to use the RFID-reader piggyback, but slightly offset from the other electronics. The reasons are alone in optics. The electronics and the I will hide in the closet somewhere. So definitely an interface is to be used, which allows such a remote operation. There I decided to use the I2C interface. So I need a board / shield which uses this interface. The assortment of shilds with a I2C-Interface is not really abundant. If man / woman still needs a reading distance of at least 5 cm, the antenna size is already playing a major role.   So I ultimately decided on the RFID-board of Adafruit (ID: 789) . The board is delivered already prepared for the I2C interface using the Arduino ports

So as to avoid collisions on the ports between the the shields/boards, you should plan the using of the ports carefully.  
The SPI-interface is natively using the following pins:  
MOSI ( M aster O ut / S lave I n) pin D11 (fixed)  
MISO ( M aster I n / S lave O ut) pin D12 (not changeable)

SCK (Slave Clock) pin D13 (fixed)
SS / CS ( S lave S elect or C hip S elect) Pin Dx (changeable)

The I2C interface of the reader consists of:

SDA (serial data),
SCL (serial clock)  

In addition to the ports above we use  the IRQ (interrupt). It does not belong to the I2C interface.

The following table shows the proposed pinout:

Dx = Digital I / O, Ax = Analog I / O

Who is interested in more profound information of the  SPI and I2C interface, should have a look at the  this german seminar .

All devices on the I2C bus must have a unique address by which they can be identified and addressed on the bus. It would be important to know what address has the RFID reader. We'll do that later. There are so-called sniffer (sniffer).

Next time we look at the RFID board and have closer look to the inner life. Now you could say "unimportant", but it isn't as unimportant as you think .