Which arduino to use with TTL 3.3V & baud rate 57600 to communicate with reader?

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1

I have a Tagsense ZR 100 active rfid reader. The reader sends out TTL(3.3V) data at a baud rate of 57600 bps ,no parity,1 stop bit,no flow control.There is a TTL(3.3 V) interface on the board as shown in the manual.

I want to interface the TX and RX pins to the arduino for serial communication.Now I am not sure which arduino board to use.Will arduino due be the best for me considering the ttl 3.3 v level and a high baud rate?

2

If you look here:

http://www.wormfood.net/avrbaudcalc.php

You're going to want a 16MHz Arduino (or a Due), since 57600 is just not reliable at 8MHz. The problem is, Arduinos (except the Due) don't like to run at 16MHz at 3.3V. So, if you want to use an off-the-shelf Arduino, it's going to need to be a 5V model and that means level shifting.

If you're willing to go beyond an off-the-shelf Arduino, you could roll your own 7.3728MHz Atmega and run it at 3.3v. Or, it may be possible to take a stock 3.3V Arduino and desolder the crystal/resonator and put a 7.3728MHz crystal/resonator in it's place (of course you'll need to burn a new bootloader with the proper settings).

3

Hi,
you can use an Arduino UNO with a voltage divider to get 3,3V from the TX pin of Arduino to RX pin of your rfid reader.
This is an example:

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4

[quote author=Dario Gogliandolo link=topic=187450.msg1387507#msg1387507 date=1378911929]
you can use an Arduino UNO with a voltage divider to get 3,3V from the TX pin of Arduino to RX pin of your rfid reader.
[/quote]How about the reader Tx to the Arduino?

I've actually done this, and it worked for me, but I don't know if reading a 3.3V digital signal on a 5V Arduino is reliable/acceptable practice?

5

The Arduino UNO should interpret the 3.3v as high signal, you can try to connect directly the TX of your reader to RX of Arduino.

6

See the datasheet. For the AT chips (eg the 386 for the uno) running at 5v anything above 3v will be seen as a high!

Mark

7

holmes4:
See the datasheet. For the AT chips (eg the 386 for the uno) running at 5v anything above 3v will be seen as a high!

I'm looking at section 28.2 DC Characteristics on page 313 and it appears that anything above 0.8V will be read as high.

I'm no expert though... I'm probably reading it wrong.

As I said, I've successfully read a 3.3V serial signal from a 5V Atmega328P. I just don't know if it's good practice.

8

I like to use these with my UNO when connecting to 3.3v logic devices -