RE: Electronics question

["Neil Wrightson" <neilw@xxxxxxxxxx>]

Hi,

Actually, 3.5 V is enough for RS232C communication. The voltage levels must
be between 3V and 15V.
That is a logic 0 is between -3V..-15V and a logic 1 is between +3V..+15V.
A voltage between -3V..+3V is deemed to be in the nomans land and an
illegal
value.

RS232 voltages were not intended to be used as power supplies.
It just happens that older equipment could typically supply ~20mA at these
voltages so people/companies took advantage of this.
This was more the case when the actual driver IC i.e. 1488 had it's own
external +/-12V supplies fed to it and it just switched these supplies.
IC's such as the MAX232 run directly from the +5V rail and generate their
own +/- supply usually in the +8/-8 voltage region.
Which is still a legal voltage.


Regards,

Neil Wrightson.


_____

From: ukha_d@xxxxxxx [mailto:ukha_d@xxxxxxx] On Behalf Of
Kevin Hawkins
Sent: Friday, 26 June 2009 1:09 AM
To: ukha_d@xxxxxxx
Subject: Re: [ukha_d] Electronics question





Could it be anything as simple as some configuration parameters for the
specific Avocent port in use that causes the port to assert DTR ? 3.5V
is not a large enough voltage here to work with most RS232 equipment
-and obviously isn't enough to power a 5V regulator. The port was
'open' when you made this measurement I assume.

Ant's suggestions is neat way around this - albeit requiring a secondary
PSU.

K

ant wrote:
> Hi Paul,
>
> Yeah you're pretty much there:
>
> 1) disconnect the DTR line from your circuit (belt and braces)
> 2) connect the +ve wire from a 9v DC PSU to pin 1 of the 78L05
> 3) connect the ground wire from the 9v DC PSU to one of the
> regulator's ground pins (I can't read the schematic, there might only
> be one ground pin, depends on the package)
> 4) leave the RXD and GROUND connections to the serial port
>
> cheers
>
> ant
>
>
> ------------------------------------
>
> Yahoo! Groups Links
>
>
>
>
>







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