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Rfid reader on fez hydra, can be connected?


#1

I plan to connect this module:
http://www.seeedstudio.com/wiki/Electronic_brick_-_125Khz_RFID_Card_Reader
to a fez hydra, but I’m not sure about voltages.

1-According to the specifications, output level is 5v (either serial or
wiegand), but docs says that gpio pins operate at 3.3v, so I’ll need a
level shifter to convert voltage to 3.3?

2-Someone knows about this product (the older one)?
http://www.seeedstudio.com/wiki/125Khz_RFID_module_-_Wiegand
It is not specified output voltage

Thanks.


#2

Or use this one and be up & running in 5 minutes?

https://www.ghielectronics.com/catalog/product/366


#3

Ian, what took you so long? :slight_smile:


#4

@ davidf - GPIO are 5V tolerant so you should be fine.


#5

Yes, you’re right,
I own the rfid reader module you’re suggesting. It’s tested and it works well. it’s up an running in 5 minutes, but:

1-I want to connect this rfid reader because I’m introducing myself to the world of microcontrollers, electronics, etc…and this rfid module seems a good place to start learning to integrate I/O devices. Today is an rfid module, tomorrow will be another rs-232 or a wiegand module.
2-It seems that it has a longer read distance
3-In wiegand mode, the program does not have to constantly read rs-232 for data, it uses Interrupts to signal the data (if I understood right).
4-The anntena can be placed appart of the module, and can be replaced/improved
5-Can be used as an extension of other modules that accepts wiegand inputs/outputs, or used with other boards.

A) Where I can find if it is safe to plug a 5v signal to input pins?
B) can I configrure any GPIO ports as interrupt port, as explains in
https://www.ghielectronics.com/docs/5/digital-inputs

I just want to be sure my board will not become part of the decoration of my house!

Many thanks for an answer, I’m sure it has been asked or it is documented somwhere, but for the moment, I’m a bit lost.
Again, thanks for your patience.


#6

@ davidf - Each MCU is different. Check the MCU datasheet, it should indicate which pins are interrupt capable. In general pin 3 on many sockets is guaranteed to be an interrupt pin.

https://www.ghielectronics.com/docs/120/gadgeteer-sockets


#7

Gotta work sometime… :wink:


#8

According to datasheet, pins on FEZ Hydra ARE NOT 5V tolerant. Post #55 here https://www.ghielectronics.com/community/forum/topic?id=5884&page=6 also confirms this.


#9

Ok, many thanks for posting.
YOU saved me from buying another mainboard!!!

finally I’ve found where in the docs is explained.
It’s in the
"Beginners Guide to C#
and the .NET Micro Framework"
Chapter 6.2: Digital inputs:
(I never thought I would find the answer in a document titled “guide… to microframework”)

“All GHI Electronics boards use processors that run on 3.3V
so the highest voltage the pin should ever see is 3.3V. This is true for ChipworkX and FEZ Hydra but not for EMX. EMX is 5V-tolerant. This means that even though the processor runs on 3.3V, it is capable of tolerating up to 5V on its inputs. Most digital chips that you would be interfacing with are 5V. Being 5V tolerant allows us to use any of those digital circuits with our processor.”

So it seems that ONLY EMX is 5v tolerant!!. I’ll need a level shifter.


#10

As was pointed out, the actual place to find this is in the processor data sheets…

Do you need to write to the device, or just read ? Assuming just read date, you only need to worry about one line.

Step 1 I would suggest is to try to run the device at 3v3 instead of 5v and see if it works.

Step 2 would be to throw a couple of diodes on the RX pin (the TX out of module) to get it down to 3.6v, or to get it even closer to 3v3 you can use a voltage divider (two resistors). You might have that stuff sitting around rather than buying a level shifter


#11

Its 2 line input only (in wiegand mode), no write.

Nice, that’s easy. I’ll have a try

Ok, to design electrical circuits is beyond my capabilities, but I’ll try with this converter which I bought just in case:

Many thanks Brett, all comments are really appreciated, specially by new users.


#12

@ davidf - Sorry for misleading answer earlier. :frowning:


#13

You should be fine with the SF shifter - but the electronics of the diodes or the resistor network aren’t onerous either, let us know if you want more info ever…


#14

No matter, you 're trying to help.
someone said: An expert is a person who has made all the mistakes that can be made.