Dienstag, 5. Februar 2013

5. Sound the RFID-card out

And so I have bought the following RFID-card : Adafruit ID:789. As it should be, I first checked out what is available for it at Adafruit. In this moment I'm only interested in hardware-informations.  In the data specifications you can find several tabs. Let's have a look one after another:

Tab "Description"
Here you can find descriptions and valuable information on the structure of the board. Those who intend to use the SPI interfacesghoul read those informations. In short: Reading required  

Tab "Technical Details"
Only showing the size specification is IMHO definitely a little poor. I had always expected data on power consumption in different states. What voltages are / can be used? Sorry, no answers.  

Tab "Tutorials"

  • Very good additional information about RFID. Here I was able to find more in-depth data of the RFID card, which I will use. I use Mifare S50 Classic - cards. In that document there is more to find. Really worth reading!
  • Since I will not use the function of NFC phones and I have not looked in there ', I can not judging this point.
  • The other information are data sheets and time charts. The data sheets can answer many questions, if you don't know how to go on.I come back again to the data sheets
Here I have been led on a false trail. At this point you have to be extremely careful!

The links to the libraries guide us to the required I2C-sketches. I will try them at a later date.

The antenna design is based on the use of the RFID chip from NXP PN532. This one is used on my board. So far ok

It is said that the schematic diagram will follow later, but there is a link that works - and point on the diagram of the breakout boards (ID: 364) ! I have not noticed it right away, and asked me how it is with the power supply and the levels on the inputs and outputs. The data sheet tells me that the max. voltage is 3.6 V. Input and output levels are at 3.3V. The question Is: How can I adjust the voltage? The tutorail shows namely the breakout board with an additional level adjustment. Do I need it? Then I searched the forum at Adafruit and had been successful. In a post dated 11/13/2012 someone asks for a diagram of the NFC Shield. In response, there is a link to github, where there is among others a *.brd and a *.sch file. What the hell I have to/can do with the file? The program associated with this format is called eagle and is available in the Internet for download. During installation, you can choose a free version with limited options (eagle-light). And then I see in the diagram (*.sch file) what I need:

Copyright Adafruit
Both lines the SDA and the SCL have ever used a level shifter. The IRQ line, does not require a level converter, as it is an output of the RFID-board and the input of the Arduino will work properly with this voltage. The same question what to do with the 3.3V supply voltage is cleared by the diagram:

Copyright Adafruit
The Shield has a fixed voltage contrller "onboard". It converts the 5V into the necessary 3.3V.  

Therefore the board has everything my heart desires!

But where is what on the board? This time tomorrow I'll have look at the *. brd file.