RS-232 problem. Please help
By Perkins - usenet poster
Hi everybody.
I've made a circuit that gets power from RS-232 pc connector. This
circuit works great on some computers and don't on others, and it
driving me mad. The problem is: when switching on I get a fantastic
4.67v in the IC vcc input pin and the circuit works ok, but when
trying on another computer I get a low 2.20v in the IC vcc pin and the
chip doesn't works, why it works right on several pc's and don't on
others? What is the reason fot the vcc difference with the same
circuit but different pc's.
Please help
Solution #1
posted on Aug 11, 2005
Luisa_K - usenet poster
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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.
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.
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Solution #2
posted on Aug 11, 2005
Charlie - usenet poster
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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
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
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Solution #3
posted on Aug 11, 2005
Ross - usenet poster
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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)
<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)
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Solution #4
posted on Aug 11, 2005
Reynolds - usenet poster
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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
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
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Solution #5
posted on Aug 11, 2005
maartenw - usenet poster
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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
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
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Solution #6
posted on Aug 11, 2005
Chandler - usenet poster
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On Mon, 21 Jun 1999 09:42:49 -0400, "Olin Lathrop" <o @cognivis.com>
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
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
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Solution #7
posted on Aug 11, 2005
Janice - usenet poster
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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
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
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Solution #8
posted on Aug 11, 2005
Hart - usenet poster
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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.
capability accross different manufacturers. Either use a different source
of power, or redesign the circuit to use less power.
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