Easiest LED indication of rs232 activity?

[Frode Undseth]

Hi all!

I'm trying to figure out the simplest way of getting a visual indication
of activity on a rs232 Tx line. I know rs232 is using +-12V for signalling,
but is it possible to drive a led through a resistor directly between the
signal line and 0V withouth weakening the rs232 signal too much? Has
anyone tried this, or are there other better, cheap and simple methods
I could use?

Any idea is appreciated..

Thanx for any help!

Kind regards,
Frode Undseth

 

[Mjolinor]

"Frode Undseth" <fun.arctic@heating.no> wrote in message
news:1069763743.271658@gurney...

Hi all!

I'm trying to figure out the simplest way of getting a visual indication
of activity on a rs232 Tx line. I know rs232 is using +-12V for
signalling,
but is it possible to drive a led through a resistor directly between the
signal line and 0V withouth weakening the rs232 signal too much? Has
anyone tried this, or are there other better, cheap and simple methods
I could use?

RS232 doesn't use 12v it is current controlled not voltage, the open circuit
voltage is around +-15 volts but is useless for most things. You need to use
an op-amp monostable circuit to get any useful indication off the TX line
directly.

 

[Kale]

Yes, I have.
forget those op-amps etc. A led and a resistor is enough.
Don't use leds with two colors, it is very difficult to see activity in a
line. Better use two leds for one line, one for positive and one for
negative voltages. If you only need to see the activity of tx (and rx?) line
then one led could be enough, althoug you then can't see when the line is
powered but not active.


"Frode Undseth" <fun.arctic@heating.no> wrote in message
news:1069763743.271658@gurney...

Hi all!

I'm trying to figure out the simplest way of getting a visual indication
of activity on a rs232 Tx line. I know rs232 is using +-12V for
signalling,
but is it possible to drive a led through a resistor directly between the
signal line and 0V withouth weakening the rs232 signal too much? Has
anyone tried this, or are there other better, cheap and simple methods
I could use?

Any idea is appreciated..

Thanx for any help!

Kind regards,
Frode Undseth

 

[Jim Thompson]

On Tue, 25 Nov 2003 12:55:53 -0000, "Mjolinor" <mjolinor@hotmail.com>
wrote:

"Frode Undseth" <fun.arctic@heating.no> wrote in message
news:1069763743.271658@gurney...
Hi all!

I'm trying to figure out the simplest way of getting a visual indication
of activity on a rs232 Tx line. I know rs232 is using +-12V for
signalling,
but is it possible to drive a led through a resistor directly between the
signal line and 0V withouth weakening the rs232 signal too much? Has
anyone tried this, or are there other better, cheap and simple methods
I could use?

RS232 doesn't use 12v it is current controlled not voltage, the open circuit
voltage is around +-15 volts but is useless for most things. You need to use
an op-amp monostable circuit to get any useful indication off the TX line
directly.

Now where did you get *that* misinformation ??

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

 

[Mjolinor]

RS232 doesn't use 12v it is current controlled not voltage, the open
circuit
voltage is around +-15 volts but is useless for most things. You need to
use
an op-amp monostable circuit to get any useful indication off the TX line
directly.



Now where did you get *that* misinformation ??

I don't know, I always thought that's the way it was so which bit is
mis-information?

 

[Jim Thompson]

On Tue, 25 Nov 2003 15:25:22 -0000, "Mjolinor" <mjolinor@hotmail.com>
wrote:

RS232 doesn't use 12v it is current controlled not voltage, the open
circuit
voltage is around +-15 volts but is useless for most things. You need to
use
an op-amp monostable circuit to get any useful indication off the TX line
directly.



Now where did you get *that* misinformation ??


I don't know, I always thought that's the way it was so which bit is
mis-information?

Current. Go look at a 1488 data sheet (my design).

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

 

[Mjolinor]

"Mjolinor" <mjolinor@hotmail.com> wrote in message
news:BvKwb.149$g15.522196@newsfep1-win.server.ntli.net...

RS232 doesn't use 12v it is current controlled not voltage, the open
circuit
voltage is around +-15 volts but is useless for most things. You need
to
use
an op-amp monostable circuit to get any useful indication off the TX
line
directly.



Now where did you get *that* misinformation ??


I don't know, I always thought that's the way it was so which bit is
mis-information?

OK, wrong. So which one is 20ma loop current? There are that damn many of
the bloody things.

You will still need a monostable and opamp type circuit to get anything
meaningful (IMHO)

 

[Rein Wiehler]

Mjolinor wrote:

"Mjolinor" <mjolinor@hotmail.com> wrote in message
news:BvKwb.149$g15.522196@newsfep1-win.server.ntli.net...

RS232 doesn't use 12v it is current controlled not voltage, the
open
circuit
voltage is around +-15 volts but is useless for most things.
You need
to
use
an op-amp monostable circuit to get any useful indication off
the TX
line
directly.



Now where did you get that misinformation ??


I don't know, I always thought that's the way it was so which bit is
mis-information?

OK, wrong. So which one is 20ma loop current? There are that damn
many of the bloody things.

You will still need a monostable and opamp type circuit to get
anything meaningful (IMHO)

20mA (or 40/60mA) was used before terminals and other devices were
equipped with RS232 connections, like teletype printers. now almost
history.

 

[Ken Taylor]

"Frode Undseth" <fun.arctic@heating.no> wrote in message
news:1069763743.271658@gurney...

Hi all!

I'm trying to figure out the simplest way of getting a visual indication
of activity on a rs232 Tx line. I know rs232 is using +-12V for
signalling,
but is it possible to drive a led through a resistor directly between the
signal line and 0V withouth weakening the rs232 signal too much? Has
anyone tried this, or are there other better, cheap and simple methods
I could use?

Any idea is appreciated..

Thanx for any help!

Kind regards,
Frode Undseth


Short answer - yes you can. Use something like a 1k Ohm resistor. The

problem with brighter is that you may not see fast pulsing, but vary it if
you like till you get something that suits.

Ken

 

[Tomi Holger Engdahl]

"Frode Undseth" <fun.arctic@heating.no> writes:

Hi all!

I'm trying to figure out the simplest way of getting a visual indication
of activity on a rs232 Tx line. I know rs232 is using +-12V for signalling,
but is it possible to drive a led through a resistor directly between the
signal line and 0V withouth weakening the rs232 signal too much?

Yes with suitably high resistance value and sensitive LED you
can get useful visual indication.

Has anyone tried this,

There are many commercial RS-232 gadgets built in this way
around. Many small boxes that you connect between two RS-232
connectors and have LEDs to so RS-232 signals just have a set
of bicolor LEDs and suitable resistors for current limiting inside
them. I don't have resistance values in hand, but I quess that
the serial resistors used in those have value of few kilo-ohms.

or are there other better, cheap and simple methods I could use?

Nothign comes to my mind that would be simpler and cheaper.

Any idea is appreciated..

Thanx for any help!

Kind regards,
Frode Undseth

--
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at
http://www.epanorama.net/

 

[Watson A.Name \"Watt Sun]

Frode Undseth wrote:

Hi all!

I'm trying to figure out the simplest way of getting a visual indication
of activity on a rs232 Tx line. I know rs232 is using +-12V for signalling,
but is it possible to drive a led through a resistor directly between the
signal line and 0V withouth weakening the rs232 signal too much? Has
anyone tried this, or are there other better, cheap and simple methods
I could use?

Any idea is appreciated..

The old breakout boxes used to use a bicolor LED with a 2.2k resistor to
indicate the signals. But the problem was that once the speeds got up
to 9600 bps and faster, the data light was barely visible.

Later breakout boxes used a single transistor to amplify the current for
each LED, and a pair of AA cells for power. That improved the
visibility a lot.

Thanx for any help!

Kind regards,
Frode Undseth

--
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[R. Steve Walz]

Frode Undseth wrote:

Hi all!

I'm trying to figure out the simplest way of getting a visual indication
of activity on a rs232 Tx line. I know rs232 is using +-12V for signalling,
but is it possible to drive a led through a resistor directly between the
signal line and 0V withouth weakening the rs232 signal too much? Has
anyone tried this, or are there other better, cheap and simple methods
I could use?

Any idea is appreciated..

Thanx for any help!

Kind regards,
Frode Undseth
-------------------

A two-color bidirectional Red/Green LED and a 1K resistor for
each one to common ground.

+12V (logic "0" TTL) is to be Red,
and -12V (logic "1" TTL) is Green.

Xmt and Rcv should be green, and the handshake lines, DTR, DSR,
RTS, and CTS and RI and CDC should be red when "redy" (ready)!
When data flows you'll see the green go to amber flickering.
-Steve
--
-Steve Walz rstevew@armory.com ftp://ftp.armory.com/pub/user/rstevew
Electronics Site!! 1000's of Files and Dirs!! With Schematics Galore!!
http://www.armory.com/~rstevew or http://www.armory.com/~rstevew/Public

 

[R. Steve Walz]

Mjolinor wrote:

RS232 doesn't use 12v it is current controlled not voltage
-------------

You are wrong and have NO idea what you're talking about, how
embarrassing for you.

-Steve
--
-Steve Walz rstevew@armory.com ftp://ftp.armory.com/pub/user/rstevew
Electronics Site!! 1000's of Files and Dirs!! With Schematics Galore!!
http://www.armory.com/~rstevew or http://www.armory.com/~rstevew/Public

 

[R. Steve Walz]

Mjolinor wrote:

"Mjolinor" <mjolinor@hotmail.com> wrote in message
news:BvKwb.149$g15.522196@newsfep1-win.server.ntli.net...

RS232 doesn't use 12v it is current controlled not voltage, the open
circuit
voltage is around +-15 volts but is useless for most things. You need
to
use
an op-amp monostable circuit to get any useful indication off the TX
line
directly.



Now where did you get *that* misinformation ??


I don't know, I always thought that's the way it was so which bit is
mis-information?

OK, wrong. So which one is 20ma loop current? There are that damn many of
the bloody things.
---------------------

75176, not 75188/189

-Steve
--
-Steve Walz rstevew@armory.com ftp://ftp.armory.com/pub/user/rstevew
Electronics Site!! 1000's of Files and Dirs!! With Schematics Galore!!
http://www.armory.com/~rstevew or http://www.armory.com/~rstevew/Public