RS-232 problem. Please help

Perkins, its not your circuit, its the pc's prob, some are using a low power version of RS-232 communications chips and wont work unless the external unit is self powered. these serial driver chips are CMOS type chips and can put up the plus and minus 12 volt swings that serial uses but push the current that a circuit like yours uses to go self powered. try tapping the usb circuits or PS2 circuits to remedy this ( i know this answer is a little late in coming but i just found this site and figured what the heck?. ) the older systems have serial ports that are more likely to work for you, or you could just redesign the circuit and use the usb ports, they are already setup for power but it is limited, very limited, four usb to serial adapters (USB POWERED) will usually put it on its knees, for figure for a max of 300 MA on the usb ports TOTAL

The RS-232 spec has to have receivers that require voltages but don't
require much current, so with either of those PCs, the serial
interface works just fine.  But your circuit requires more current,
and one PC can diliver that, but the other one cannot.

You may have to make sure that the serial port is being driven by the
right chip.  If it uses the regular 1488 or 1489 chips, then it should
work.  If it uses a newer all-in-one chip, then all bets are off.

On Mon, 21 Jun 1999 22:09:08 GMT, pete @interchange.ubc.ca (Peter

        Have you ever taken a close look at an ordinary IBM-PC type
serial mouse?  You will find that the majority of them are powered
from the signal lines of an ordinary RS-232 port quite micely.

        Jim

James Meyer heeft geschreven in bericht
<376fcd6e.36634 @netnews.worldnet.att.net>...
micely.

Quite micely indeed ;-)

Met vriendelijke groeten,
Frank Bemelman
(reageren per email ? verwijder dan de 'x' uit mijn
emailadres)

On Tue, 22 Jun 1999 18:03:34 +0200, "Frank Bemelman"

        It started life as a typo, but when I saw how apt it was in
context, I just left it in there.

        Freud would have laid it on the doorstep of subconscious
repression and Jung would have blamed synchronicity.

        Jim

I've designed several things for the serial port, and the problem is
three-fold:

1. Some portable PC's actually turn off all power to the serial ports
to save the battery.

2. Many "RSR232" levels are not truly RS232 levels. Originally, the
standard called for at least 15 mA drive at 12V. Now, many PC's
drive at 10V or less

3. The current has dropped off, too. It is almost impossible to find
any RS232 signal that will drive 15 ma into anything.

Here's the rule: If your system will run at 3V try several +V signals
driven through diodes, then regulate at 3V with one of those
"low differential" regulators. You should have about 10mA available
from any of them.

Bob

On Mon, 21 Jun 1999 09:42:49 -0400, "Olin Lathrop"
wrote:

        Or use more than one of the RS-232 lines to supply power.  Put
a germanium diode in series with each line that shows a positive
voltage and connect their cathode ends together to derive the supply
voltage.

        Jim

The RS-232 handshake lines (which I assume you are deriving your power
from) are not intended to be used as power sources.  Different RS-232
drivers may have different output current capabilities - the ones in
the computer that works can apparently deliver more current than the
other one.

Also, the RS-232 spec says that any voltage between 3 and 12 (or maybe
15) is legal - perhaps the second PC uses 3 volts...

--
Peter Bennett VE7CEI        
GPS and NMEA info and programs: http://vancouver-webpages.com/ peter/index.html
Newsgroup new user info: http://vancouver-webpages.com/ nnq

As you have discovered, there is a very large range of current drive
capability accross different manufacturers.  Either use a different source
of power, or redesign the circuit to use less power.