Interface arduino with 7V rs232

Forum 2005-2010 (read only) Hardware Interfacing
1

Hi,

I have to connect arduino to a device who have a rs232 port with 7V.
There is some suggestion there :
http://www.sparkfun.com/commerce/tutorial_info.php?tutorials_id=65&page=

What do you think about the proposed solutions.

For inline resistor, what's the typical current of each port ?

Thanks

2

What do you think about the proposed solutions.

It will not work.

This is because RS232 also inverts the signal as well as changing the voltage. Also an RS232 signal swings about ground so you will get +7V and -7V on the signal line.

You need to use a max 202 (or similar chip) to translate the signals.
I don't think you have a 7V RS232 system anyway. It's just that 7V is the minimum voltage you can have on an RS232 line. The nominal voltage will be 12V.

3

There's a neat little, inexpensive, module for interfacing RS232 and TTL (Arduino, etc) from Wulfden.

If you go to...

... and scroll a bit (10 lines?) up the page to the section heading, you can read an independent "review".

4

I have learned that the minimum voltages for rs232 is +3v and -3v and not 7v.
A max232 should do the job.

5

I have learned that the minimum voltages for rs232 is +3v and -3v and not 7v.

You have learned wrong.
The +/- 3V are the threshold voltages for determining the mark and space states they are not the minimum specified voltage drive output for a device in the RS232 specification.