AVR-Chat

On Tue, 23 Feb 2010, rsimonus wrote:

> I am curious about USB to serial db9 cable.
> I am planning to buy one. I want to know if
> any USB to serial 9pin cable which will work
> with any device and my old Sony Clie or it is
> depend on brand and model? I see walmart sell
> those for $9 dollars.

I recently got one labeled HL-340 which works
fine-it didn't need any drivers, just setting
another COM port from minicom.

Testing it was a bit difficult though.

If you want to use a DB9-to-USB cable
to communicate with a microcontroller, you
need to keep in mind that the data being
sent by the USART is

- inverted comparted to RS232 traffic

- uses TTL levels (0-5 volts) rather
   than RS232 levels (-12..-3, 12..3 volts)

You *can* try to overcome these two problems
by feeding the signals through a NOT gate
and then stepping up the voltage with a
charge pump. This is highly educational and
if you are in it for the experience, I can
highly recommend it.

... but if you simply want to communicate
from AVR to PC and get it done fast, it's
much easier to just order a little MAX232
converter board as well, hook up the USART
pins to that and be done with it.

I got something like this:

http://cgi.ebay.co.uk/MAX232-RS232-Serial-to-TTL-UART-Converter-Board-Adapter_W0QQitemZ120534212314QQcmdZViewItemQQptZUK_Computing_CablesConnectors_RL?hash=item1c10661eda

Depending on your needs you might even simply use a
TTL-to-USB rs232 interface board and skip the
DB9 connector altogether:

http://cgi.ebay.co.uk/USB-to-RS232-Module-Based-TTL-Converter_W0QQitemZ260550110677QQcmdZViewItemQQptZUK_Computing_CablesConnectors_RL?hash=item3ca9ff2dd5

Hope this helps.

Best,
Marc