Re: really simple RS232-TTL converter... does it work?

On 19 Jan 2007 11:40:43 -0800, "Dan Lenski" <dlenski@xxxxxxxxx> wrote:

Hi all,
I'm playing around with a wireless router that has a TTL-level serial
port and trying to figure out an easy way to convert it to RS-232
without having to wait for a Maxim IC to come in the mail. While
hunting around for tricks to doing this, I came across one that seems
really impressive:
http://www.botkin.org/dale/rs232_interface.htm

The "receive" portion seems straightforward: just use an n-type MOSFET
and pull-up resistor to switch the TTL output between 0 and 5V.

But the "transmit" portion seems a little dodgy: first, it relies on
the computer always putting out +12V on the RTS pin, which apparently
is the default state of that pin if you leave hardware flow control
off. And secondly, it can can only transmit 0V or +12V. And according
to the RS-232 standard, 0V is undefined (+-3V are the thresholds).

The guy who came up with this says that it has worked with every
laptop, desktop, and PDA serial port that he's tried. Kind of cool...
so I guess that most computers interpret a 0V signal as a logical 1, as
would be required to make this scheme work? Has anyone used this
simple level converter? How'd it work for you?

Thanks,
Dan Lenski


Pure TTL out usually works, and just a series resistor for the input
direction, to limit the current. Data isn't inverted, of course.

John

.

Relevant Pages

  • really simple RS232-TTL converter... does it work?
    ... port and trying to figure out an easy way to convert it to RS-232 ... the computer always putting out +12V on the RTS pin, ... so I guess that most computers interpret a 0V signal as a logical 1, ... would be required to make this scheme work? ...
    (sci.electronics.design)
  • Re: really simple RS232-TTL converter... does it work?
    ... port and trying to figure out an easy way to convert it to RS-232 ... the computer always putting out +12V on the RTS pin, ... would be required to make this scheme work? ... Using a P-channel MOSFET, you get a logic inversion, and the Tx data output ...
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  • Re: really simple RS232-TTL converter... does it work?
    ... But the "transmit" portion seems a little dodgy: ... the computer always putting out +12V on the RTS pin, ... so I guess that most computers interpret a 0V signal as a logical 1, ... would be required to make this scheme work? ...
    (sci.electronics.design)