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I have one controller which processes data from a weigh scale. With it I can capture data using hyper terminal on a PC (RS232 communication - standard DB9 connector). Now I want to analyze it on another PC as well.

Unfortunately, my controller has only one RS232 output. Can I tap another RS 232 from the existing signal cable (by stripping the cable, taking out parallel signals and all)?

Or I need to use any custom hardware or cable?

Ah well, that was my original question, and I did try using the circuit, the problem is I can receive data only on one terminal. The splitter is not working. Totally Clueless now. Any Ideas ???

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marked as duplicate by PeterJ, Daniel Grillo, Majenko, placeholder, W5VO Jun 20 '14 at 16:53

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

yah i think what you showed is possibly the best solution for me, but the explanations of that diagram is a bit sketchy, can you kindly explain the circuit plz ??? – RicoRicochet Jun 20 '14 at 11:51
I'll add some more details to that answer shortly. – PeterJ Jun 20 '14 at 11:55
I guess I have got the hang of it, making the connection. Thanks a ton. – RicoRicochet Jun 20 '14 at 13:25
Com0com or its cousin hub4c com0com.cvs.sourceforge.net/viewvc/com0com/hub4com/… – kenny Jun 20 '14 at 13:25
Well, the connection, did not work. Any help / ideas / suggestions regarding the splitter ??? – RicoRicochet Jun 22 '14 at 4:35
up vote 7 down vote accepted

You can connect one output to multiple inputs, but you cannot connect multiple outputs to one input.

That means you can connect the line that transmits data from your scales to the PC to a second PC, but you cannot connect the two lines that transmit data from the PCs to the scales.

So yes, you can "tap in" to the transmitted data, as long as you only want to read the data.

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Wouldn't it also be necessary to ensure that the "tap" does not load the line? This would only work assuming distances were short and no loading occured, right? – sherrellbc Jun 20 '14 at 14:13
Inputs are generally high impedance. Two inputs instead of one would increase the load, yes, but from very very tiny to very tiny. You would have to go some to make any noticeable difference. I often do TTL level RS232 sniffing with a pair of USB->UART adaptors with very rough cabling and it works great even at very high baud rates. – Majenko Jun 20 '14 at 14:37

I have used a modem splitter from time to time. I don't really care for them, but with some resistor wizardry they do work.

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