How to use an STP Cat5E cable for safer long cable serial communications connections

This is a tip, that I received from the owner of: http://www.eastelectronics.gr/. Please, try at your own risk. As per http://www.connectworld.net/cable-length.html, serial cable maximum length can range between 3 and 50 meters depending on the communication speed. Another source of quality information regarding serial cabling and connections is to be found at http://www.arcelect.com/rs232.htm, where it is claimed that a (not suggested) maximum length of a serial cable could reach even 1.3 km.

However, for long cables Radio Frequency Interference (or RFI) and Electro-Magnetic Interference (or EMI) might destroy not only the signal, but also valuable equipment in PC or dataloggers. Following the invention of UTP and STP cables, which can provide immunity to interference (see next figure)

half modem RS-232 communications (that is three cables: Rx, Tx, Earth) can be set, with STP cable, as per the schematic below; this may protect both your signal and your equipment. Nevertheless, one should stress that the correct solution for a really long serial communication is to use isolation techniques available both in literature and as commercial products. Most such commercial products convert the RS-232 signal to RS-485.  Here is the schematic in two parts, the "Left" End (up) and the "Right" End (down): 

LEFT END

RIGHT END

Obviously, Earth cables should be connected together.

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