Easiest LED indication of rs232 activity?

signalling,

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.

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.

signalling,

Now where did you get *that* misinformation ??

...Jim Thompson

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|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
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I love to cook with wine.      Sometimes I even put it in the food.

circuit

use

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            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

to

line

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.

signalling,

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

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

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.

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

--
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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.

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------------------- 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

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

-Steve

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or

---------------------

75176, not 75188/189

-Steve

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